# Sticky  ECM8000 microphone measuring techniques and usage discussion



## Anthony

Okay, so BoomieMCT and I did a battery of tests on our ECM8000 mics.

The setup was my M-Audio MobilePre preamp, test amp, Magnepan MG10.1. Mic stand was set 3 feet away, 2' off the ground aligned with the ribbon perpendicular to the panel.

Nothing on the speaker changed during all the tests, the mic stand was kept horizontal for all the horizontal tests and vertical for those tests (all done at once to minimize any changes).

Measurements were full sweeps in roomEQ wizard, 4 repeat average. 1/3 Octave smoothing.

We'll start with the comparing his and my mics in horizontal and vertical. The Top trace is comparing his and mine horizontal. The Bottom traces are the vertical ones.

In the second graphic, the top traces are my mic horizontal versus vertical and the bottom ones are his mic horizontal versus vertical. Horizontal is purple, green is vertical for mine.

I'll post more later, but you can see the mics agree very well across mics and horizontal versus vertical up to about 1kHz. Above that all bets are off, although some patterns emerge. More info to follow.


----------



## Anthony

So it looks like the vertical response is smoother than the horizontal (not surprising), and there is significant variation between the two mics in the upper octaves.

So the first conclusion I would draw is that for bass response only, these mics are probably okay. The two tested only started varying at 800 Hz, so not bad for subwoofer testing.

Another thing that struck me is the top octave roll-off that is in every measurement. I don't see this in any of the correction files for this mic, so I'm wondering if this is more of a soundcard issue.

It shows up even when using the left channel as calibration and when I use the amp output as calibration (through a voltage divider), so the only explanation was that the phantom power circuitry and preamp in the MobilePre might be adding that. Boomie and I have plans to text using his mixer to see if that still shows up.

But it's clear that this mic needs independent calibration for tweeter testing. There's just too much variance and uncertainty.

So first I'm going to confirm that my sound card is not introducing too much error in the FR (if it is I have bigger problems :sad: ), after that I'll have to see what my options are.

A $120 calibration fee seems reasonable, but lately I've been hearing about better mics that are cheaper and slightly more expensive mics that are ruler flat. So I'm not sure what I'll do, but it's always nice to have more information.


----------



## Anthony

Here's the same horizontal versus vertical with the amp calibration in the loop.

Not much change, although there is a slight correction for the amp that seems to roll off about 1dB at 20k (but that does not explain the rest of the rolloff completely).

Horizontal is Purple and vertical is Orange.

For those of you who are so inclined, I like the voltage divider setup. It allows the calibration to occur after the amplifier so your reference measurement includes amp response. This way, you've eliminated all but the mic, speaker, and room (sadly those are the biggest contributors, though). Do NOT use the amp output as calibration unless you know what you're doing, though. You can easily fry your soundcard. It took me a lot of research to get the input impedance of the card, and I measured the output of the amp at different setting and sized the jig/divider accordingly.


----------



## brucek

> So it looks like the vertical response is smoother than the horizontal (not surprising), and there is significant variation between the two mics in the upper octaves.
> 
> So the first conclusion I would draw is that for bass response only, these mics are probably okay. The two tested only started varying at 800 Hz, so not bad for subwoofer testing.


hehe, we're gonna have to agree to disagree on this issue. 

Actually, I feel the mics show very good consistency between units (as we've always claimed).

It's very difficult to draw too many conclusions when comparing microphones this way. Small microphone element positional differences can account for very large changes in the measurements, particularily as the wavelength gets shorter and in areas where the response is changing rapidly. You could obtain the same differences using exactly the same mic under those test conditions. Better conditions would be to measure a near flat response in a very damped room ensuring the mic elements were perfectly at the same spot. Hard to do.

Even under the conditions used here, the different mics and different orientations showed remarkable closeness (although I'm not too fussed about the way you changed scales on every graph). Worst case under the worst condtions at high frequencies, the two mics still only show up to 4dB difference. You could get this by moving the same mic a fraction of an inch.....

My conclusion would be that these are quite good mics for the price and full range measures can be taken with some confidence in the home environment.

brucek


----------



## Anthony

Hey Bruce, I think the only real disagreement comes in the top octave.

First off, the scale changed because I was constantly moving curves around in order to separate them and group them. In fact I couldn't even find the original scale on some of the measurements.

Overall, you are right, these results are close for a majority of the measurements.

In my case, I'm most interested in the tweeter section, though, and that's where things start to become different. when you are trying to set tweeter levels or design a notch filter, the response at that end is very important. 4dB is a lot in crossover design! Most of the effects, though can be explained. For instance, the waviness in the horizontal measurements coincide with a baffle effects for a very small baffle (the diameter of the mic). Keeping the mic vertical avoids this.

As to methodology, I can say with certainty that the center of the mic capsule was within a mic capsule diameter for the measurements. I was very careful to measure distance off the floor and use an index mark to set mic location (verified via crude plumb bob). Levels were never adjusted past the initial setup.

So I'm going to recommend people use this mic vertical whenever possible for full range stuff. It seems to be how it was designed (based on other research, not just the results posted here)

The good news is that for bass, the mic-to-mic variation is very small and seem to agree with the calibration files (not pictured here). Good news indeed.

So to summarize:
For REW -- great mic, cheap, available cal files good enough, use whatever orientation you want

For two-way crossover design -- good mic, available cal files good enough up to 3kHz or so. Orientation still probably does not matter (within +/- 1dB).

For three-way, or full range work -- okay mic. Good value, but the response gets peaky. Definitely get calibration done if you want accurate results. Pay attention to orientation of your cal file and beware the "baffle" effects in the 4k to 8kHz region. Use vertical where feasible (the peak is not as great and the response is a tad smoother).

Overall a good value, unless you want to bother building your own. Probably still the best choice for REW/BFD work.


----------



## BoomieMCT

brucek said:


> hehe, we're gonna have to agree to disagree on this issue.
> 
> . . .
> 
> You could obtain the same differences using exactly the same mic under those test conditions. Better conditions would be to measure a near flat response in a very damped room ensuring the mic elements were perfectly at the same spot. Hard to do.


I don't think Anthony is trying to say that what the plots show are the anechoic responses of the mikes. The things he's trying to point out is a) the difference in the ECM-8000's response in the vertical vs. horizontal mounting and b) differences between different units.

Given the graphs shown I'd say there is compelling evidence to show that there is a consistant difference between both mounting orientations and a consistant and repeatable difference between the two mikes in the top octave. 

I don't think this was a slam on the ECM-8000 but rather some thoughts on better understanding how to use the mike as well as its limitations.


----------



## brucek

> I don't think Anthony is trying to say that what the plots show are the anechoic responses of the mikes. The things he's trying to point out is a) the difference in the ECM-8000's response in the vertical vs. horizontal mounting and b) differences between different units.


Yes, of course I realize that.

I just don't happen to agree with the conclusions (and gave my supporting arguments why I feel that way).

brucek


----------



## <^..^>Smokey Joe

I have to agree with Bruce, dispite your best efforts to align the mics to the same spot a very small difference could result in different reports. Try placing the same mic in and out several times with repeated runs(atleast 4 times) then take the average. Do the same for each mic. 
This may help average out positional differences.

I used to work in the sound recording business a few years ago, so spent alot of time with mics. Moving a mic a fraction could make all the difference between good and bad no matter how good or bad a mic is. 

Just imagion the room with lots of square boxes(interference patterns), each frequency representing a size, those that fit perfectly to the room shape will do different things to the ones that don't. If you are placing that mic right on the edge of those interference patterns you will get varying results that can be quite dramatic. ie a frequency can cancel completely with a pure tone creating areas with no sound and tone in zones that are shaped like a box.

Scuse the pun but you could be just looking at noise.


----------



## Anthony

I was one step ahead of you. I just did tests where I moved the mic a random bit. I also measured much closer to the speaker to eliminate as much of the room effects as possible.

The mic tip was around 16" from the speaker. Maximum move was about 3/4" in or out, side to side.

You can see some things that jump out as positional (green trace in both graphics), but some general things (humps, dips, rolloffs) are evident.

First one is horizontal, second is vertical, last is horizontal versus vertical (I picked one of each that was in the middle).

So, I stand by my assertion that there is a difference between horizontal versus vertical (it may just be the reflection/baffle effect of the mounting body of the mic). It might not mean anything to an RTA measurement or general wide-band EQ -- but it is significant enough for tweeter crossover/notch filter design (which is why I went down this road).

However, this mic is pretty flat up until the "unpleasantness" in the top two octaves. Good news if someone is just getting it to EQ a sub or see the effects of some room panels. 

But for any serious tweeter work, calibration is definitely necessary.


----------



## Anthony

I also made a cal file using some of these measurements. It might not calibrate to flat -- but it will calibrate to my existing Magnepans (not exactly a bad speaker to design to  )

That'll work for now. I'll probably send the mic off to Caldwell next month. I'm interested to see if my "fake" calibration file is anywhere close 

Thanks for the input. Disagreements or no, I just want to understand and get the bottom of this -- no matter how complicated. I guess that's part of the fun :nerd:


----------



## BoomieMCT

Yeah, position errors aside, the delta between my mike and Anthony's stayed the same every time we did different runs. Also the difference between horizontal and vertical was very repeatable.


----------



## Anthony

I have some followup data (that was actually in front of me all along, I just did not have perspective for it)



> Omnidirectional microphones are capable of very flat response over the entire audio spectrum because only the front of the diaphragm is exposed to the incident wave, eliminating the phase cancellations experienced with directional microphones. *However, there is one caveat.* Omnidirectional microphone response to a plane wave becomes increasingly directional as the diameter of the diaphragm becomes comparable to the wavelength of the frequency being measured. Low frequencies "flow" past the diaphragm without incident. High frequencies, however, cannot bend around the microphone structure. They pile up on the diaphragm surface causing a rise in pressure that is higher than the pressure in the surrounding field (This is one manifestation of acoustic diffraction)


-- "Testing Loudspeakers", Joe D'Appolito, page 54

he goes on to say how "free field" microphones try to counter this by controlling the resonance and damping. I guess better mics do a better job at completely eliminating this phenomenon. Entry level mics like the ECM8000 do not. Which is a shame, because older cal files that I've seen for the 8k show only a small bump in the response. The newer ones (mine included) show a big peak and rapid falloff -- apparently some are worse than others.

It probably has something to do with the capsule change (as Panasonic no longer makes what was used in the older ECM8000's). 

Hmm, maybe a DIY microphone is in my future :bigsmile:


----------



## brucek

> High frequencies, however, cannot bend around the microphone structure


Exactly, and this was my original disagreement with comparing these mics. At short wavelengths, they are extremely sensitive. I like your idea of the DIY. I've come across lots of exposed capsule DIY mic tests with the old Panasonic unit - and others. That would make a great tweeter test mic. I've seen some really inexpensive (couple bucks) capsules that are sold with calibration files that would work great.

brucek


----------



## BoomieMCT

brucek said:


> Exactly, and this was my original disagreement with comparing these mics. At short wavelengths, they are extremely sensitive.


Two reasons I don't agree. First off we are mainly noticing differences in the last two octaves (5kHz - 20kHz). This represents wavelengths of 2.7 - 0.7 inches. I'd say that assuming you have to get the mikes lined up to within a half wavelength that is still well within our test stand / plumb line capabilites. Anthony shows in post #9 that the position errors were minimal. 

The other point is that our results were repeatable. We could switch back and forth between Anthony's and my mike and the difference in the readings stayed the same. Similarily the differences with the same mike between vertical and horizontal were very repeatable.


----------



## Anthony

Bruce, I came across this schematic for the ECM8000 online. The words needlessly complicated come to mind. It amazes me how those capsule mics have such simple schematics and the ECM uses this one.

I wish I knew more about op-amp circuits (I'm good with filters and other LCR stuff, but transistors and diodes are out of my league) -- so I could tell what's going on there.

It may be as simple as Behringer designed a circuit for the old capsule, didn't change it for the new one, now the new ones are "compensated" for a different response -- therefore the peak that was tamed in earlier versions is now a problem.

I'll look into it, it seems like a fun side project. Also, a guy over at DIYAudio e-mailed me about an article testing a bunch of different mics. Apparently there are some offerings from Naiant and Beyerdynamic that blow away the ECM8000 (one cheaper, one more expensive -- although both are much cheaper than the EarthWorks models).

This weekend I'm going to rerun some frequency tests of my center channel baffle using these corrections. If all goes well, I may just use my "quasi correction" and be done with it.


----------



## Anthony

Boom,
We seem to all be nit-picking very small differences and disagree on what we consider important. Like any religious argument, the smaller the difference, the bigger the controversy :devil:

Anyways, I think we've shown that for the vast majority of uses, these mics behave rather wall unit to unit and are reasonably flat up to 5kHz, regardless of orientation.

It is comforting that using the same unit in different measurement batches shows almost no variation. so you can believe what you measure on Tuesday is as accurate as what you measured on Monday. 

As for orientation differences, I still claim that there is a difference in both bandwidth and amplitude of the hump and the measurements show it. Now, how important this is debatable. For room equalization, bass response, ****, even 2-way crossover design, it would make absolutely no difference. 4dB in the top two octaves is only marginally outside the overall system accuracy (+/- 1dB).

But for more sensitive tweeter work, it's definitely important (as my trial and error notch filter attempts have shown me) to have as accurate a measurement as you can and 4dB or a couple kHz of bandwidth are very important and make the difference between a bright speaker and a dead one.

So everyone who bought an ECM8000 can relax, unless you have to put a notch filter at 13khz, your mic is pretty good.


----------



## Rich Jura

I have 9 of the ECM 8000 and access to An Earthworks TC 30K. Next week I'll post a comparison
graph .If I recall correctly they are quite similar.I'm not that concerned about 10K to 20K as
motorcycles and gunfire in my youth took care of that.

Later
Rich


----------



## glaufman

Anthony said:


> I wish I knew more about op-amp circuits (I'm good with filters and other LCR stuff, but transistors and diodes are out of my league) -- so I could tell what's going on there.


I may be able to help here, depending on exactly how in depth you want to go, and how far you can take it yourself... but this schematic is not completely correct...I have to make a few assumptions or answer a few questions.... 

this circuit is in the mic itself? not a separate mic amp? It gets "phantom power" from an external device? that voltage comes in on BOTH XLR 2 and 3, and is referenced (or returned) to XLR1?


----------



## Anthony

I think so. I got this off of a website that shows how to mod the ECM8000, so this is the schematic of what's in the mic (not a preamp).

Phantom voltage is applied at 48V to pins 2 and 3 relative to pin 1 (chassis/earth ground).

Someone over on DIYaudio looked at this and had some comments on the design. It serves two functions: to break the signal from the capsule into two components to send balanced over the cable, and to make sure the bias voltage stays consistent on the capsule.

I was confused because similar design mics use a bias voltage across the condenser element, but just put out an unbalanced signal back to the preamp. That is obviously a much simpler circuit.


----------



## brucek

> this circuit is in the mic itself? not a separate mic amp?


Yep....



> It gets "phantom power" from an external device?


Yep...



> that voltage comes in on BOTH XLR 2 and 3, and is referenced (or returned) to XLR1?


Yep...

brucek


----------



## glaufman

OK... so how much more info are you looking for? Would I be telling you things you already know if I said the SA transistors are forming a differential amplifier that provides the balanced output, and some gain, the BC transistor is an input stage for that amp, to provide impedance matching between the mic element and the diff stage (matched impedances make for the most efficient energy transfer) and also to provide some gain...
The resistors all set the bias for the transistors, but at the same time define the input/output impedances and gain of their particular stages? The 1uF caps allow the signal to pass from stage to stage while keeping the biases separate...


----------



## Anthony

That's good information. I always like learning more about circuits.

What I was really fishing for, was whether or not there is any sort of filter designed into this to compensate for anomalies in the frequency response. For instance, a notch filter at higher frequencies. It does not look like that is the case.


----------



## glaufman

Well, C6,7,9,10 certainly limit the high frequency response, but I wouldn't call it a notch filter, looks more like a lowpass... where's the cutoff, you ask? I dunno... have to review some textbooks to calculate that... frankly, easier to measure it... or even better, look at the cal file...


----------



## Anthony

That's the whole problem I was addressing, the cal files that are floating around the internet don't work for my mic in the top two octaves.

Also, even on the cal files, it is hard to differentiate between "baffle" (the enclosure and front face of the mic), capsule, and electronics effects in the mic.

At this point, this is more of a learning exercise. I am content to make my own cal files and revise them as I make more measurements. As of now, the top two octaves are based on a semi-nearfield (1') measurement of my Magnepan MG10.1 ribbon tweeter. Worst case, I have a cal file that matches its performance (and if its performance is flat, I have a good cal file  )


----------



## brucek

> I always like learning more about circuits.
> 
> What I was really fishing for, was whether or not there is any sort of filter designed into this to compensate for anomalies in the frequency response


No, there's no audio filter here. The small RC ladders on the outputs are way outside the audio range (those are pico-farad capacitors for HF noise).

The circuit is kinda interesting. It's purpose in the first single-ended stage (BC118) is mainly to provide high impedance buffering for the mic element. The second stage creates the out of phase balanced signal with a matched output impedance to reduce noise for long mic cables.

You can see the mic element and first buffer stage are biased from the simple zener circuit, while the output stage is turned on directly with the phantom voltage.

There's really no gain to speak of (it's all buffering and impedance matching). The first stage is a typical common emitter connection using feedback with no bypassing. The non-bypassed feedback provides for very high stability even if the temperature or beta of the transistor changes. There's a huge voltage/power gain loss in this configuration, but that's fine, since stability is more important here. They've used a high value for input impedance to the first stage so the element isn't loaded. My napkin calculation puts the gain of the first stage at less than 1.

The second stage is interesting. The single ended output transistor feeds an emitter follower configuration to drive the positive XLR 2 output that has been biased on by the phantom voltage. They take advantage of that stages collector lead signal (that is 180 degrees out of phase) to pass through the bottom transistor (that is also biased on by the phantom voltage), and then out the XLR 3 lead. This configuration allows them to use a matched set of pnp transistors to produce a balanced (differential signal). The matched components ensures a consistent output impedance for XLR 2 and XLR 3 to offer pretty good noise reduction.

This circuit makes the total mic itself light years better than simply using a stand alone element.

brucek


----------



## Guest

BoomieMCT said:


> Yeah, position errors aside, the delta between my mike and Anthony's stayed the same every time we did different runs. Also the difference between horizontal and vertical was very repeatable.


To add another data point: I've been experimenting with various real time analyzers running on my laptop. While measuring pink noise with my ECM8000 I can clearly see that the 10kHz+ part of the spectrum shifts up by at least 5dB when I point the mic at the speakers, and goes back down when I orient it vertically. The rest of the spectrum doesn't change when I re-orient the mic, and nothing changes much if I move it around without changing the orientation.


----------



## Dennis H

*ECM8000 distortion*

Hey guys,

I don't get over here often enough. This thread and the ECM schematic got linked over at AVS and I was a bit concerned with the schematic. Siegfried Linkwitz has done a lot of experimenting with the Panasonic capsules and has some DIY designs on his web page.

http://www.linkwitzlab.com/sys_test.htm#Mic

In part, he says: 



> When the cartridge is connected as described by Panasonic it produces fairly high distortion at moderate SPL's and is marginally suitable for serious recording and measurement purposes. The microphone itself is extremely linear, but the built in FET amplifier stage is not configured optimally.
> 
> Fortunately, is it possible to modify the external connection to the FET. This involves some delicate work of cutting a trace on the tiny pcb in back of the cartridge and soldering thin, flexible wires to the standard two hookup points, and making a different connection to the capsule housing.


I noticed that the ECM has the capsule wired the conventional way. Obviously they aren't going to do surgery on every capsule. I wondered if their circuit might overcome SL's objections so I emailed him a copy of the schematic and asked. I received a prompt reply (the guy is a real gentleman) and here's what he says.



> Hi Dennis,
> 
> This mic will definitely suffer from distortion.
> 
> Too bad,
> 
> SL


FWIW.......


----------



## vrsound

The ECM8000 is not alone in this phenomenon. In recording orchestras for film sessions we use the omnidirectional Neumann M150 (or if you can find one the original M50). One of it's characteristics is that the high frequency response is very non omnidirectional past 2kHz. Besides it's amazing sound quality this is one of the reasons it's used so much for the Decca tree recording technique. It is not a cheap microphone costing around $6,000 - $7,000. In the Decca configuration there are always 3 of them (That's around $20k for 3 mics). The M150 was never meant to be a measurement microphone as the frequency response chart shows, but it is also not truly omnidirectional. 

If the ECM8000 exhibits this type of polar pattern as well then wouldn't it be correct to say the the horizontal orientation would be the only position that would be correct to measure HF response?

I guess the correct question to ask is what is the orientation for the flattest frequency response? 
My guess would be on-axis to the intended target. Not really what you want for a measurement microphone but at this cost, beggars can't be choosers!!

Vince


----------



## bjs

I finally got around to checking out my ECM8000...the results are consistent with the data shown by Anthony in his first post. My mic has almost 5 db variation between horizontal and vertical and even in the best orientation still has several dB of peaking. The test results were entirely repeatable. Sadly, this mic is not suitable for full range speaker testing. 

What is the least expensive *calibrated* mic available? Hopefully some resourceful person has found one that mere mortals can afford!


----------



## Guest

I realize this thread is old, but I think many people may arrive here looking for info about the ecm8000. I can help with the explanation of the schematic posted and something more...
In order of the signal path:
- C1 (3n3) is a low pass filter, 6dB/octave, cutoff or -3dB point at about 16KHz. Changing it for 1n or less improves the high end response without any undesired side effects. If you're going to change this, use a ceramic 330p to 1n capacitor.
- The intended function of the first transistor, BC118 or BC331 (Behringer has used both), is to make the unbalanced signal a balanced one. At the emitter and collector we have the same signal as in the base (input), but at lower impedance and one inverted with respect to the other. The gain is 1 (0dB). But there is a flaw here: to work as intended C6 should be connected to the emitter of this transistor instead of to ground. I have not opened any of my ecm8000s to see if actual circuit has this mistake or is only the schematic that has the mistake, but no doubt it's a mistake. The effect of this flaw is a 6dB loss of level and SNR when connected to balanced preamps. As is in the schematic, this transistor would do nothing except adding some noise.
- The last two transistors are emiter followers for each of the two balanced signals. Their only but very convenient function is to lower the output impedance. As emitter followers, the gain is obviously 1 (0 dB). C6, C7, C9 and C10 make low pass filtering, the cutoff frequency is 200KHz, well above the audio band. R12 and R13 improve the slope of the low pass filter and provide provide stability and protection against highly capacitive or inductive loads at the expense of raising the output impedance a bit. Still the output impedance remains at an excellent low value. So everything right at this stage.
- So the total gain of the circuit is 1 (0 dB), so it does not have nor need any feedback loop. The design is very good except the flaw described above, that most probably is only in the schematic and not in the actual circuit (I may confirm this if I open my mic sometime).
--------------
Some people modify the capsule to use its FET as a drain follower instead of a common drain amplifier to raise the maximum SPL (sound pressure level) handling. This is completely unnecesary for any purpose other than close drum micing or measurements at levels above 115dB SPL (permanent ear damaging levels). If you intend to make this modification, note that you must also add an ultra low noise amplification stage immediately at the capsule output. When using the capsule's FET as a drain follower, we loose all the amplification we had as common drain amplifier, and because the very low level provided by the electret mic, we need to correctly amplify it very close to the capsule to avoid a severe degradation of SNR. Regardless of author's claims, every amplification circuitry I have seen designed by people that does such modification is simply lame and will convert your good balanced mic into a lot noisier, much higher output impedance and unbalanced ouput one, incompatible with pro mic preamplifiers, only with a bit higher SPL handling and that only in some designs. If you really need to improve the maximum SPL handling of this mic and modify the capsule as drain follower, keep using the original balancing buffer, that's pretty good, and simply add a common emiter amplifier with some feedback between the capsule and the balancing buffer. Use a bipolar transitor, not a FET: after the capsule's FET, we have a low enough impedance so we want here the smallest equivalent input voltage better than the smallest equivalent input current, so a bipolar is better here). Some modification is also needed to the power suply scheme: the added amplifier stage and the BC118 should be powered by more voltage than 6V, but can't be powered from 48 since most small signal transistors can't handle that, ideal would be around 24v given that most small signal transistors specify a maxVce of 30v. A simple zener and a capacitor would do it well. If done this way, the result would be a very similar balanced low impedance mic, with 12dB higher maximum SPL handling and most probably (depends on the added stage) only a bit noisier than the stock ecm8000. Even further you may add a switch to bypass the added amplifier stage for really high SPL handling above 130dB, supposing that the electret itself could handle that. Note that you increase the minimum phantom power requirement to 24v, and that the mic pre you connect it to must be able to handle very high levels. The maximum output of the mic this way would be near +20dBu, while even the highest end pro Yamaha preamps clip at -14dBu without padding or -4 with padding, but many other manufacturers allow near 0dBu levels at mic inputs without padding, and some even handle more than +10dBu. Anyway, all this is only is to use this mic for purposes very different for which it has been designed.
-------------
About the frequency response of this mic, what I have found is that there have been very different production series. My mics are all from the very first series, and sure don't match any of the responses I have seen reported by other owners in the net. I have not sent them to a lab for accurate calibration but I have a high end B&K 4007 measurement mic and by comparison I'm sure my ecm8000s don't show shuch an exagerated peak near 10KHz, but something between +1.5..+2.5dB. So what I got was cheap and reasonably good measurement mics, but you can not trust the high frequency part of the actual piece you get without calibration or at least comparison with another mic you can trust. And if you have to calibrate, you can use actually any small condenser or electret. I purchaed the ECM8000 to avoid moving my B&K (I drop it once and repair cost was $1200), and I was satisfied with its performance, but because I'm using a portable computer for measurement, now I find much more convenient one I made based in a subminiature $1 capsule mounted in a thermoretractile tube of only 5mm diameter. When I calibrated against the B&K, I found this $1 capsule was excellent, even better than my ECM8000s, and nicely fits in a small pocket of the portable's suitcase.


----------



## Anthony

Good insight. Thanks for the information.

And welcome to the Shack!


----------



## hifisponge

*Re: ECM8000 Tests (several pics)*



Anthony said:


> Okay, so BoomieMCT and I did a battery of tests on our ECM8000 mics.
> 
> The setup was my M-Audio MobilePre preamp, test amp, Magnepan MG10.1. ...
> 
> The Top trace is comparing his and mine horizontal. The Bottom traces are the vertical ones.


Anthony - 

I came across your thread while trying to troubleshoot what I see as a problem with the HF response in my own measurements. I own speakers that use a Scan Speak Revelator 9500 tweeter that is supposed to have flat FR up to 30KHz, yet when I measure them, there is a sharp roll-off above roughly 15KHz. I see a similar problem with the graphs you published. 

Here's what I get when I measure one of my speakers at 1M using the ECM and no cal file (vertical mic position).









Here is the response plot of a typical ECM mic as provided by Cross-Spectrum labs.










There is nothing that I can see in the above plot or in the generic cal files that would indicate that the ECM mic rolls off sharply before 20KHz. I also use the M-Audio Mobile Pre, so I wonder if this is contributing to the issue. I would love to get to the bottom of this.


----------



## Anthony

Hmm, I had not thought of that. I tell you what, I have another calibrated mic on loan to me right now. I will run a couple of sweeps with that in the mix and see if that rolloff is still there. If so -- an M-Audio problem. If not, still and ECM8000 problem, but at least it's narrowed down.


----------



## brucek

> If so -- an M-Audio problem.


How could it be an M-Audio problem, if a full loopback soundcard calibration file was created and returned a flat line after a measure?

brucek


----------



## Anthony

The loopback is done on a 1/4" to 1/4" unbalanced connection. Not exactly the same circuit as the balanced mic and phantom power. So if that part of the circuit is causing problems it would be impossible to "cancel" it out with the loopback channel.

There is no balanced out of the MobilePre, so you can't even loopback XLR to XLR on the other channel.


----------



## brucek

> The loopback is done on a 1/4" to 1/4" unbalanced connection. Not exactly the same circuit as the balanced mic and phantom power.


Loop unbalanced out, into the positive differential amp (pin 2) of the XLR mic-in using a pad.

brucek


----------



## Anthony

What about the phantom power? IIRC, that was the original concern that having phantom power on that circuit would be be a problem for the unbalanced input. I seem to remember asking M-Audio tech support and they never got back to me (which is odd because they usually got back to me with answers pretty fast).

I have the cables to do that with (XLR to RCA with RCA to 1/4 adapter). If I can verify that it's not putting 48V DC on the unbalanced connection I'll give that a shot.


----------



## brucek

> What about the phantom power?


Just shut it off with the front panel switch.

You also need to make the little pad to lower the level from line to mic level... I can advise you on that.

When all is said and done, you'll probably find that the mic amp offers a small drop off in the lower end and the upper end will be fine. But, I suppose it never hurts to test it, and of course when you're done you'll have the file to use.

For example, here is my XENXY showing the line-out to line-in (yellow) and then compared against the line-out to mic-in through a pad (green). See how it drops a bit extra at the low end (inconsequential, really, since 10Hz is almost 0dB difference))) and then see no change at the upper end. 










brucek


----------



## Anthony

I thought you meant to run the loop that way during measurements (in which case the phantom power had to be on).

what kind of divider? I have a test jig for speaker workshop that does a voltage step down while impedance matching. But now that I think about it, it matches the power amp and line out of the Mobile Pre. Hmm, I'll have to think about this more.


----------



## Anthony

I found this:
http://www.uneeda-audio.com/pads/

I think I can make the 100:1 pad at the bottom using a barrier strip and some open ended wires to suit. Then run a calibration sweep and check the results.

I'll still run that second mic just to be sure, but this should only take me about 10 minutes to gin up.


----------



## brucek

> I think I can make the 100:1 pad


Here's a very suitable -30dB attenuator that will lower line to mic level from unbalanced to a balanced XLR mic.

I drew it for you in Visio below. Very simple. 

Hook it up and create a soundcard cal file and save it. 

Then measure to be sure of your flat line.

Remove the loopback and use that channel for measuring.











When you're done, tell us how much different the soundcard file is from the previous line-out to line-in file.

brucek


----------



## Anthony

Alright, I'll give that a try tonight and post the calibration results (1/4 to 1/4 and 1/4 attenuated to mic). thanks.


----------



## brucek

> I'll give that a try tonight and post the calibration results


Great, whenever you get the time, I think it will be a benefit to others who will ask if they should be concerned about the mic preamp portion of the M-Audio Mobile Pre. I suspect that the mic preamp will not be significant in relation to the standard line-in to line-out calibration that most do. 

I've proven that the XENYX802 preamp is not worthwhile including in the soundcard cal routine, and this will add another to the list (or not). Now we'll know for sure.

Many users aren't really capable of this fabrication (as you are), so this will be a help... If possible, it would be good to see the graph in the same scale as mine above, with vertical = +/-30dB and horizontal of 2Hz-25KHz.

brucek


----------



## hifisponge

Anthony said:


> Alright, I'll give that a try tonight and post the calibration results (1/4 to 1/4 and 1/4 attenuated to mic). thanks.


Thanks for taking this project on Anthony. I certainly don't have the experience needed to construct the attenuation circuit to test the mic input.

All the best,

- Tim


----------



## Anthony

Okay, some results:
Dashed is the Line to Line (1/4" to 1/4" unbalanced), Red is Line to Mic with an attenuator circuit to match the levels.

The only difference in the two is the scale. I was expecting differences in the high end and found none, but the low end was pretty interesting. Not a huge difference, but measurable for 20Hz up a bit.


----------



## hifisponge

Anthony - 

So I guess that rules out the M-Audio sound card / preamp. Must be user-error on my part somewhere.

What do you make of the HF roll-off in the graphs you displayed in your first post? What might be the cause?

- Tim


----------



## Anthony

Nope, see the new thread I've started. I have more results that just add to the confusion. I split this thread into a new one to discuss just the MobilePre and the ECM8000 so we can figure out what's going on.


----------



## brucek

*Re: MobilePre ECM8000 oddities*



> Okay, some results:


Nice work Anthony. So, the results are as expected. The low end is a bit off and the upper end is much the same. Even down to 10Hz, it wouldn't matter too much which file you use, so I think we're safe in advising members that a line-out to line-in for external soundcards is suffice for the soundcard calibrate loopback test.

brucek


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Okay, more weirdness. Below is a series of measurements I made with the new soundcard cal file (which seemed to only affect the low end anyways).

Speaker is a Magnepan MG10.1. Measurements were at the listening position. Red is the current ECM8k cal file, Blue is the old cal file, and Green is the Rat Shack meter used as a mic (with appropriate cal file and C weighting)








So with 2 different mics, I get the same fast rolloff in the top octave. It looks like the new mic file fixes the baffle "bump". 

To see if it's a vertical/horizontal thing, I ran a semi-nearfield measurement of the speaker both horizontal and vertical using the new "split" ECM8k cal file.








Purple is vertical, yellow is horizontal. Both have the rolloff at 15kHz.

So I believe we've ruled out the mic, and via nearfield measurements ruled out the speaker. It's not the calibration or loop, but it seems to be the soundcard. 

Any thoughts folks?


----------



## brucek

*Re: MobilePre ECM8000 oddities*



> Any thoughts folks?


Well, it's as expected. The old ecm8000 cal file did not account for baffle step, and the new one does. The plots of the cal files themselves easily reveals why the two ecm graphs of the speaker are different. I do have more confidence in the newer ecm file (as far as generic files go).

The RS meter reveals what we already know about the RS meter, in that somewhere between 3KHz and 10KHz they all demonstrate a peak. Simply not usable above 3KHz.

brucek


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

But still, you figure the ECM would show a better top octave than the RS meter and yet they still both show that steep drop above 15kHz. 

Hmm, I think my next project may be to build one of those condenser mics from scratch and see how it performs. If for no other reason, to learn more about what goes into all this. I've had enough tweeter crossover problems that I want to make sure I have something I trust up there (and I don't have $500 for a EarthWorks  )


----------



## brucek

*Re: MobilePre ECM8000 oddities*



> So I believe we've ruled out the mic, and via nearfield measurements ruled out the speaker. It's not the calibration or loop, but it seems to be the soundcard.


I don't see how it could be the soundcard if your loopback measures flat to 20KHz. That completely eliminates the soundcard. It's the only thing you can be sure of...

I don't think you can be 100% sure of the mic until you have it calibrated.

How have you ruled out the speaker?


brucek


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

I just find it to be too much of a coincedence that both anthony and I are showing a steep roll-off in the HF above 15KHz. I show it when using both an ECM Mic and DBX mic.

Here are a series of nearfield plots I took using the DBX mic. The different plots represent on-axis, slightly above, slightly below, and to the left and right. (I was trying to find some axis, any axis, that I would get flatish treble response above 15KHz).










I'll be getting my calibration files for my DBX mic this week, but Cross Spectrum has already sent me a preview of the plot, and there is no roll-off in the HF, so I don't expect the cal file to fix this problem. In fact the DBX mic's response looks very similar to the ECM, just with less of a hump at 10KHz.


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

Anthony - 

I'm not sure that the Maggies are a good reference for this test. I've read in the past that it is difficult to get an accurate FR reading of panel speakers because of the way they project sound.

For reference, I looked for FR measurements done by AV mags on the maggies and found these:

Magnepan MMG W (measured by Ultimate AV Mag)









Magnepan MG 3.6 (measured by Ultimate AV Mag)









As you can see, they are showing a fairly steep roll-off in the upper HF. Do you have any other more conventional speakers around to test?

Here's what my speakers are supposed to be doing in the HF.

Wilson-Benesch speakers (measured by Hi-Fi News UK)


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Heh, I wonder if Ultimate AV is using our mic 

That's a good point, though, about testing other speakers.

I have some Adire HE10.1's (don't know why that number is in both of my speaker sets  ) in the tube system upstairs. I can bring one downstairs and remeasure.

Panel speakers radiate in a "middle finger" lobe pattern (for lack of a better image). The on-axis is very strong but narrow then flanked by weaker lobes around the 15 to 30 degree mark, then another null and another set of even weaker nodes around the 45 degree mark. Overall it looks like the classic figure 8 pattern of a dipole, but with nulls inbetween the fingers. A neat trick to getting a great center image is to aim the speaker so the second lobe is aimed at the listening position (about a 30 degree toe-in). It's weird but it keeps a pretty stable center image across the stage without the dreaded "sweet spot".

Anyway, I was measuring about 8 inches from the panel, which should be enough for the ribbon and panel to integrate, but you are right, all it takes is for the mic to be in the wrong null and the FR goes all wacky. 

I'll try the other speakers tomorrow night. I can also try a raw BG Neo3PDR and Neo8PDR tweeter/panels to see how they fare.

Thanks for the input guys, it'll be great to get to the bottom of this.


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Well, I just looked through some old measurements and this is not apparent in all of them -- just the ones of the Magnepans. Some random measurements don't seem to have it (like almost touching the panel nearfield), but almost all of the 1m to 3m measurements do. Hmm, I guess I started with a bad assumption, since the speaker was supposed to be flat to 24kHz. But dipoles are tough to measure, tweeters are tough to measure, and in-room is tough to measure. So dipole tweeters in room must be really tough to measure 

My guess is it's some sort of cancellation effect from position or frame/panel. Sorta like a broad comb filter effect. It's too high to be dipole cancellation and the likelihood of me putting the mic in an exact null every time is slim. I'm just thinking out loud here to try and find a solution that fits your problem as well, Tim.

I'll test those horn tweeters tomorrow and check back. Seems we're at least a bit closer.


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

Hmmm ....

I ran some more measurements, and I don't know what I did differently but I'm able to get respectable HF extension when I use the mixed cal file for the ECM mic, BUT only when I point the mic at the speaker .

Yellow plot is horizontal mic position, blue is vertical.


----------



## robbo266317

I have been prototyping a new setup, which is why I found this forum. I have never had a tool like REW before! All I can say is WOW. Anything else I said would ensure that the moderators would delete it. 
Anyway, I would not be in a position to comment without REW, So...
I couldn't get the ECM8000, However the local shop did have a JBL re-badged DBX TRA M for a similar price. So I bought it and a small mixer to supply power and set about measuring my new speaker. (singular)
I have been extremely happy with the JBL as my Shiva X measures (close field) to what was modelled in WinISD for a 120 litre cabinet. ie ~7 Db down at 20Hz.
As for the top end, this mic happily did a good job of following the Raven 3.2's response with no major anomolies.
If you cannot find the ECM then I can quite happily suggest using the JBL.


----------



## brucek

> JBL re-badged DBX TRA M for a similar price.


What microphone calibration file are you using for it?

brucek


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Nice measurements there. Interesting that the JBL tweeter has that top octave falloff as well -- not exactly a cheapo tweeter in its own right.

I'll post mine tonight in this exact same format. You said 1 foot, 6ms gate (from zero, or from first impulse received?). The candidates will be the MG10.1 ribbon tweeter and the compression tweeter used in the Adire speaker. I do not remember the brand name on it, but it screwed into the back of the Eminence woofer.


----------



## brucek

*Re: MobilePre ECM8000 oddities*



> from zero, or from first impulse received?


In the IR window popup (after the measurement is complete), I set 1msec in the Left Pre-Window and 5msec in the Right Post-Window, and then Apply to the measurement.

brucek


----------



## robbo266317

The one from the DBX RTA-M usable thread http://www.hometheatershack.com/for...-cards/13006-dbx-rta-m-calibration-curve.html

Here is a screenshot:


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Okay, my results:
Red = Maggie, Vertical Mic
Green = Maggie, Horizontal Mic
Orange = Adire, Vertical Mic
Blue = Adire, Horizontal Mic

View attachment 11936


Gates were 6 ms, "Split" ECM8k cal file, 12" from tweeter on axis. 1/2 octave smoothing. Shifted to line up like curves.

You can see the trademark split between horizontal and vertical orientation of the mic in both sets of curves. 

However, most notably, the Adire HE10.1 does not show the fall-off that the Magnepans show. Very interesting. I stared with a bad assumption and look where it got me 

So at least now I have renewed confidence in the mic and soundcard, but less in the Magnepans


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

So, it looks like the New ECM cal file, horizontal orientation is the best for direct measurements.

Behringer insists that vertical is better for diffuse field measurements like pink noise and such, but since 90% of my measurements are drivers and speakers directly, I will stick with horizontal.


----------



## brucek

*Re: MobilePre ECM8000 oddities*

Yeah, I think we can assume the ECM and the cal file are fine.

The Maggies still go fairly high, and unless your hearing is really top notch, I doubt you'd be disappointed in the sound.

The Adire measures quite good for sure....

Maybe we should be listening to music instead of swept tones..... :heehee:

brucek


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Bruce, to me that is music! :nerd:


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

Bruce & Anthony - 

A big thanks for helping me troubleshoot, and for all of the effort you two have put into this series of experiements. I'm still waiting for my DBX mic and cal files to come back from Cross-Spectrum and I will post my results when I get those. In the meantime, I think I'll do another run with the ECM and split cal file.

Bruce, can I ask a favor? Would you please retest at 3 feet (horizontal mic) to see if that induces some roll-off in your Proacs? And would you also measure on the midrange axis as well? You're Proac's use a tweeter that is similar to mine and I want to see if distance affects the HF response and also what sort effect being off-axis has.

Thanks,

- Tim


----------



## hifisponge

Robbo - 

I have the DBX mic, and I just had it calibrated. I don't think that cal file listed in the link you provided is all that accurate. It only shows about a 1.5dB rise in the treble response of the mic, when it is really more like 5dB.

- Tim


----------



## robbo266317

Hi Tim,

The close mic scan of my raven 3.2 is fairly flat from 1k to 25k. (As per it's measured graph that came with it)
I can repost just the 1k to 25k graph if you like.


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

Looking a little deeper at your guys' graphs vs. mine, both of you are showing a difference of roughly 6dB at 20KHz in your horizontal vs. vertical mic positions. This difference coincides with the differences shown in the FR plot of the ECM mic. My measurements show a difference of 12dB at 20KHz. What's up with that? :nerd:


----------



## brucek

*Re: MobilePre ECM8000 oddities*



hifisponge said:


> ..........can I ask a favor? Would you please retest at 3 feet (horizontal mic) to see if that induces some roll-off in your Proacs? And would you also measure on the midrange axis as well? You're Proac's use a tweeter that is similar to mine and I want to see if distance affects the HF response and also what sort effect being off-axis has.


Well, you got lucky, since I hadn't returned my ProAcs to their regular spot in my main system, I was able to do another test for you.

Anyway, I thought I would divide your test in two.

I had a couple of small graphs of my particular speaker model, that were done in an anechoic chamber at 50" (reasonable far-field measure). I thought I would try and duplicate the test conditions for those two graphs.

The first graph is the tweeter and mid-range individually tested on-axis at 50" and shown separately on the small graph.

The second is a measurement of the mic placed first between the tweeter and mid-range at 50" on-axis and then at 30 degrees off-axis in the horizontal plane. The plot is averaged across the 30 degrees horizontal window. 

It seemed reasonable to carry out these two tests.

The graph below is the anechoic graph showing ~1KHz to 30KHz. 
This is the on-axis, taken at 50" of the 1" SEAS tweeter and the on-axis of the 7" ScanSpeak mid-range driver. Note the rise that I experienced when I measured my tweeter at 12".









The graph below is the anechoic graph showing the average across a 30 degrees horizontal window, measured at a point vertically equal between the tweeter and mid driver at 50". 
The comments about the graphs in the article says, _The tweeter has a gently rising on-axis response all the way to 30kHz, but it is very directional above 15kHz. This results in a more or less flat response when averaged across a 30 degrees horizontal window_.









I think my measurements below support what the anechoic responses show, in that the tweeter is certainly good past 20KHz when on-axis, but drops off at about 15KHz when off axis in the vertical or horizontal plane. This may be what you're experiencing somewhat, where you're suspecting your measurement equipment. But the way to be sure is to measure near-field on-axis, and that will prove it if the response doesn't drop prematurely.

Anyway, below is my first graph, measured at 50". 
The mic is on-axis with the tweeter for the purple line, and then horizontally moved to 30 degrees for the green line (with the mic still pointing at the tweeters center). 
I also shortened the gate to 3msec to remove some reflections from the stand or wires or whatever it was. I did check the gating envelope in each case on its impulse response. All these are plots with no smoothing.
You can see the drop off when it's off-axis.









Below is simply an average plot of the above two measures (an REW feature allows averaging of multiple plots). 
It shows that there is a decent response to 20KHz within a 30 degree horizontal window of the tweeter.









Now I do the same experiment, except the mic is moved down to point at a spot equidistant between the mid-range driver and the tweeter.
Note that the vertical off axis from the tweeter creates a drop off at both on-axis (horizontally) and at 30 degrees (horizontally).









This is simply an average plot of the above two measures. It shows that there still is a fairly decent response to 20KHz off axis within a 30 degree vertical or horizontal window of the tweeter.











> My measurements show a difference of 12dB at 20KHz. What's up with that?


If you examine my two plots, I measured a 12db and 10db difference.

brucek


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

Bruce - 

You rock! :bigsmile:

Thanks a million for taking the time to conduct all of those measurements. They explain a lot and put my mind at ease. I also did some digging around for graphs of the ScanSpeak tweeter used in my speakers and found that that they all showed about a 12-15dB drop above 15KHz when measured 30 degrees off axis.

The difference between the tweeter in my speakers vs the one in yours is that it does not have rising response on-axis. In fact, based on measurements I did last night, it is about 3db down at 20KHz on-axis, so the off-axis roll-off above 15K looks more pronounced. 

My measurements still don’t quite match those published on the ScanSpeak tweeter, but they do appear to be within a reasonable deviation.

Thanks again.

- Tim


----------



## hifisponge

Robbo - 

I was under the impression that you were using a JBL / DBX mic with a cal file that was published on this site. If that is the case, I was only suggesting that if you want accurate high-frequency readings from that mic that you should have a cal file made for your specific mic.

- Tim


----------



## hifisponge

*why it pays to have your mic professionally calibrated*



brucek said:


> That seems consistent with the graph of mic orientation versus response...
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> brucek


Bruce, Anthony - 

I got my DBX mic back from Cross-Spectrum Labs today and the response graphs the provided explain at least part of the roll-off I was getting when I did my measurements with this mic. You see, I was doing all of my measurements with this mic in the vertical position, as I thought that was the way to get the flattest response from an omni mic. As it turns out, the DBX mic is 6dB down at 20KHz when used vertically, with a +2dB hump at 11KHz. In the horizontal position there is a 5dB peak at 11KHz and it flattens out by the time it reaches 20KHz. I would post the FR plot, but I was only given a paper graph.

For the record, the cal file I have now is significantly different that the one that was posted by another user in this forum, and neither is good to use when the mic is in the vertical position.

Cheers,

- Tim


----------



## brucek

*Re: MobilePre ECM8000 oddities*



> and neither is good to use when the mic is in the vertical position.


It's my understanding that your mic was calibrated to be used in the vertical position, when placed in a room in a diffuse field (such as the listening position). That would mean it is accurate to rely on the results if you use the cal file in REW under those normal conditions.

The only time it would be inaccurate is when you take a close speaker measurement of the tweeter, where you need to point the tip horizontally at the speaker, and so the cal file is not accurate for that upper octave. Is that not a correct assessment?

Comments?

brucek


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*



brucek said:


> It's my understanding that your mic was calibrated to be used in the vertical position, when placed in a room in a diffuse field (such as the listening position). That would mean it is accurate to rely on the results if you use the cal file in REW under those normal conditions.
> 
> The only time it would be inaccurate is when you take a close speaker measurement of the tweeter, where you need to point the tip horizontally at the speaker, and so the cal file is not accurate for that upper octave. Is that not a correct assessment?
> 
> Comments?
> 
> brucek


Herb with Cross Spectrum initially gave me just a horizontal cal file, but upon request also provided a vertical cal file.

In regards to the proper orientation, I was just discussing this with herb last night. Here's what he said:



> For in-room speaker measurements / room-correction, 90-degree (vertical mic position) is *good enough* - these are free-field microphones which assume that sound will be coming around from multiple directions, but *there will be a some error at the top end*. When doing room measurements, I always recommend people measure at various locations (in three dimensions) to minimize orientation errors as well as the effects of room modes.
> 
> When performing loudspeaker freq response measurements, using the mic at a 90-degree angle is a no-no because it's not designed for that at high-frequencies. At the highest frequencies (say, 3kHz and up), the wavelength of sound is small enough that the mic body itself will start to interfere with the wave propagation. At a 90 degree angle, part of the wave collides with the body of the mic and the rest of it grazes across the surface of the diaphragm, so the diaphragm no longer moves as a piston and what the microphone 'sees' isn't actually representative of the wave form if the mic wasn't there.


Personally, because I want more accurate HF measurements, even at the listening position, I'm inclined to use the horizontal mic position and appropraite cal file all the time. I’ve also been thinking for a while now that there is merit to the belief that we humans give priority to the direct sound in the mid and high frequencies (over the combined direct + reflected sound) so it would seem that pointing the mic in the direction of the speaker would give a bit more weight to the direct sound while still capturing the reflected. Then again, I suppose this can also be addressed with reduced gate times.

Thoughts?


----------



## robbo266317

I totally agree Tim. 
Each mic will be different since they are mass produced. 
For critical measuring you will need to get it calibrated. Mine seems to be adequate for the purpose using the generic file and the tests I have done shows it is acceptable out to about 25khz. 
Since my upper range these days is only about 13.5 khz I am not too worried. 
I could calibrate it myself using the graphs supplied with the Ravens. :bigsmile: 
I'm glad I purchased them when I did, as two months later they doubled in price because the aussie dollar dropped. They are now $3,750 each out here.
http://www.audiomarketplace.com.au/...oduct_id,118/option,com_virtuemart/Itemid,49/

I hope you have air-conditioning. It's going to be another scorcher over there again.


----------



## spearmint

*Re: MobilePre ECM8000 oddities*

Thanks for the conducting the tests and posting the results.

Anyone have any negative thoughts regarding using the Mobilepre?


----------



## hifisponge

*Re: MobilePre ECM8000 oddities*

Spearmint - 

Both Anthony and I have concluded that the issue we were experiencing had nothing to do with the Mobil Pre. It works as advertised. :yes:

- Tim


----------



## Anthony

*Re: MobilePre ECM8000 oddities*

Yeah, the MobilePre is a great portable sound card. I even use it to tie into my laptop as a mobile music station (laptop to MobilePre to stereo). Good for measurements. 

It does have some flaws if you want to use it for speaker building. The line out sags its voltage under even light loads, which makes it tough to measure impedance. It is also a bit noisier than some of its counterparts (again unless it's for really serious speaker testing it's not an issue). But the portability aspect and phantom power make it worth it.


----------



## Anthony

Okay we've merged the threads back together since they both ended up being a discussion of the ECM8k mic and its usage (originally they were split b/c I thought one would end up being a MobilePre discussion).

So back to one big thread folks! :whistling:

Carry on!


----------



## spearmint

hifisponge said:


> Spearmint -
> 
> Both Anthony and I have concluded that the issue we were experiencing had nothing to do with the Mobil Pre. It works as advertised. :yes:
> 
> - Tim





Anthony said:


> Yeah, the MobilePre is a great portable sound card. I even use it to tie into my laptop as a mobile music station (laptop to MobilePre to stereo). Good for measurements.
> 
> It does have some flaws if you want to use it for speaker building. The line out sags its voltage under even light loads, which makes it tough to measure impedance. It is also a bit noisier than some of its counterparts (again unless it's for really serious speaker testing it's not an issue). But the portability aspect and phantom power make it worth it.


Thanks, very much appreciated...


----------



## brucek

An interesting response from Cross Spectrum Labs here in regard to mic orientation for measuring.

Does it mean we should stop recommending vertical orientation of the ECM8000 type mic when measuring from the listening position? :dontknow:

brucek


----------



## Sonnie

The question might be for those measuring 5.1 or 7.1 full room response, for something like Audyssey type measuring, does the mic need to be turned and pointed at each speaker as the tones/pulse moves from speaker to speaker? Or should we assume Audyssey has accounted for vertical placement of the mic?

And how do you point the mic at a sub, since it is omnidirectional? What if you have subs scattered about the room?


----------



## brucek

> does the mic need to be turned and pointed at each speaker as the tones/pulse moves from speaker to speaker?


Well, Herb has clarified my incorrect interpretation of what he said. His recommendation is that the mic is vertical (straight up and down) with a slight 10-20 degree tilt toward the mains speakers. 
And, if you're measuring a specific speaker near field, then it's as we already understood - point the mic horizontally on-axis at the source and gate the impulse response.

brucek


----------



## cinema mad

Sonnie said:


> The question might be for those measuring 5.1 or 7.1 full room response, for something like Audyssey type measuring, does the mic need to be turned and pointed at each speaker as the tones/pulse moves from speaker to speaker? Or should we assume Audyssey has accounted for vertical placement of the mic?
> 
> And how do you point the mic at a sub, since it is omnidirectional? What if you have subs scattered about the room?


As far as Audyssey, Chris co creator of Audyssey has stated that the position of the mic supplied for use with Audyssey should be at Ear hight and pointed verticaly directly at the ceiling, because it is designed for Grazing.. 

This works fine unless you have A speaker such as center channel tilted slightly up then it "MAY" be best to adjust the mic angle to match the angle of the center speaker, but that creates A huge hassle ....

Cheers....


----------



## Anechoic

Sonnie said:


> Or should we assume Audyssey has accounted for vertical placement of the mic?


I would presume that Audyssey has accounted for their suggested orientation of the mic and has their system optimized for that placement.



> And how do you point the mic at a sub, since it is omnidirectional? What if you have subs scattered about the room?


For low frequencies it won't matter since pretty much any (condenser) mic will omnidirectional below 1000 Hz. Point it where ever you like. :T


----------



## Wayne A. Pflughaupt

In my years in pro-audio, both professionally and dabbling around the fringes before and since, I’ve never seen anyone use a vertical mic orientation when shooting a room. Typically the mic is aimed at the speaker, so when I first saw the vertical-orientation recommendation here I thought it was the most ridiculous thing I had ever heard. However, when I found out that we were recommending vertical because the ECM8000 was calibrated that way, I let the matter drop, even though I don’t buy into it. 

Poking around the internet to bolster my case, I was surprised I wasn’t able to find much of anything to support either method. I looked up the manuals for several pro-audio hardware RTAs and even a couple of software-based programs like TrueRTA, and nothing specifically mentioned mic orientation. 

The only thing I could find supporting a horizontal orientation was a picture in the manual of my AudioControl R-130 RTA that showed the calibrated mic pointed directly at the speakers, angled slightly upward. My RTA shows that response at the listening position starts drooping as far down as _1200 Hz_ with vertical mic orientation, and it gets really severe above 8000 Hz. Having used this RTA for well over 10 years, I trust it enough to know that if I EQ’d my system from a vertical mic orientation, it would be horribly inaccurate.

Likewise, the only thing I could dig up supporting vertical orientation was something on Goldline’s website mentioning that THX recommends it for home theater systems. I find that a bit problematic, however, given the wide range of shapes and sizes of rooms that home theaters find themselves in - high ceilings, low ceilings, cathedral ceilings of different angles and pitches, shoe-box rooms, family rooms open to other areas of the house, etc. 

I don’t know how THX, Audyssey or anyone else can in good faith recommend a mic orientation that relies on reflections for upper frequency information to be applicable for all residential situations. Let us not forget that reflected sound will exhibit a certain amount of high frequency loss due to a certain amount of absorption from the walls and ceilings. If room treatments are present, the high frequency loss in reflected soundwaves will be even greater. Did Audyssey figure that into their “grazing” theory? Just a few of the reasons why I prefer horizontal orientation: You know what you’re getting with direct soundwaves.



brucek said:


> Does it mean we should stop recommending vertical orientation of the ECM8000 type mic when measuring from the listening position? :dontknow:


As long as our ECM8000 calibration file was generated using a vertical position, I don’t have a problem with us recommending it _for that mic._ 

However, a while back someone was asking about orientation who was using a dbx mic from one of the company’s RTAs, and we recommended vertical. _I think we need to make it a point to tell people to use the orientation that was used to generate their calibration file._ If that information is unknown, horizontal should be the standard recommendation, at least for anyone taking full-range measurements. Even if it’s not specifically stated anywhere “on record,” it’s generally accepted that any mic calibration is performed horizontally, unless specifically stated otherwise. 

Regards,
Wayne


----------



## glaufman

Interesting information and discussion... although you guys are the experts, my thoughts...
I fully agree with using the mic in the orientation the cal file was generated in, in ALL cases... anything else has potentially zero accuracy... 
Assuming you can get a cal file generated for any orientation you want, if you're willing to pay for it, the question of preferred orientation for different applications, has to depend on the characteristics of a given mic... starting the the ECM8000...
Seems to me that any measurement intending to be a direct measurement, i.e. either ignoring/minimizing reflections and/or in an anechoic setup, point the mic directly at what you're measuring, use a cal file taken in that orientation, and go...
But I question the validity of room response measurements taken horizontally as it seems the body o fthe mic would obviously affect the response to room reflections ... polar plots could prove me wrong... 

For low freqs the effects of the case surrounding the mic shouldn't affect things significantly, and at high freqs, when talking about room response, are we really looking for a kind of accuracy where a cal file taken in the verticaly orientation would not adequately account for the diffraction/grazing affects?

I can't comment on Audessey as I have no first-hand experience, but I hesitate to trust any automatic process to do it's job without taking manual measurements to confirm results... "trust, but verify"


----------



## JMB

Herb,
Perhaps, you could enlighten us. 
Are your recommendations for mic placement during measurements based upon some literature that you might share or based upon your experience? 
:huh:What position do you place the mics in during calibration?

Thanks,
Jay


----------



## Anechoic

Mostly based on my experience, the experience of my colleagues and my understanding of the science involved. I don't really have any literature I can point you to.

As for what position I place the mics - it really depends on a whole bunch of factors. For smaller rooms, I usually just hit the listening spot. For larger rooms where the listening point might be spread out, I like using spacial averaging techniques either my measuring at multiple positions and averaging the curves together, or (for systems where it's not practical to use the multiple-position method) I slowly move the microphone around in large vertical and horizontal circular motions. The "sweet spot" result getting this method isn't as good as the 1-position method, but you get an improvement at the other positions.


----------



## JMB

Are you saying that for calibration you place the mic in different positions, or for measurement? 
I am really asking about the position that you place the mic in for calibration.

Thanks,
Jay


----------



## Anechoic

Are you asking about home theater system calibration or my microphone calibration?


----------



## JMB

I am asking about the microphone calibration. Sorry for being too vague.

Jay


----------



## Sonic Icons

Hi, I hope the following question for Herb isn't considered abusing a dead horse :time-out: (that has already been discussed extensively in the thread):

Can you comment, based on your measurements, on "typical" variation of the ECM-8000 frequency response between the horizontal (0 degree, on-axis) and vertical (90 degree, grazing incidence) orientation? More specifically, is it possible to give an estimate of the frequency where the splitting between the horizontal and vertical response reaches +1 dB, or the frequency where the splitting reaches +3 dB? Or, does the horizontal-vertical splitting show a large variation between individual microphones, that makes it difficult to estimate "typical" values?

I'm asking this more for general interest in "how it works" than for practical reasons. My guess is that the directionality (horizontal-vertical splitting vs. frequency) is more consistent between individual ECM-8000 microphones than the basic frequency response, because the directionality is determined mainly by diffraction of sound waves from the microphone body, and the size and shape of the microphone body is highly consistent between units. But maybe I'm overlooking something :scratch:


----------



## Anechoic

JMB said:


> I am asking about the microphone calibration. Sorry for being too vague.
> 
> Jay


Hmm, I could have sworn that I explained my process here at some point, but I guess I didn't.

Above 100 Hz, I use a free field substitution method. I mount a reference microphone (ACO Pacific 7250, calibrated by Scantek) 27 inches away from a custom speaker with a full-range (coax) driver to measure a reference response. I replace the reference microphone with the ECM8000 and repeat the test. I use the reference response to correct the response of the ECM8000 and that gets me the >100 Hz response for that particular microphone. I use this procedure to measure mics at 0 degrees and at other angles. I use ARTA (swept sine) to make the measurements.

For frequencies below 100 Hz, I use the same substitution method, but rather than doing a free-field measurements, I use a small pressure chamber to obtain the pressure response of the reference mic and the ECM8000-under-test (at low frequencies, the pressure response is equal to the free field response for omni-directional microphones).

These measurements are consistent with IEC 60268 standard for microphone measurements.

For the polar measurements, I have a mic stand mounted on a lazy susan. I mount the mic in front of a speaker playing pink noise and rotate it around 360 degrees (in 10-degree increments) to measure the 1/3 octave band responses. I have the mic mounted so that the mic diaphragm is the axis of rotation - basically the mic capsule stays in the same ~ 1 sq cm of area and the cable end of the mic rotates around the diaphragm (make sense?).

For sensitivity measurements, I have an acoustic calibrator (GenRad 1986 Omnical, also regularly calibrated by Scantek) which puts out calibration tones at several frequencies and sound pressure levels. I place the calibrator over the ECM8000 capsule, hook up the ECM8000 output to my Sencore RTA, and just read the sensitivity figure from the RTA.

For noise floor measurements, I have a soundproof chamber within which the background noise (at night) is lower than 17 dBA. Since the noise floor of ECM8000's are generally higher than 30 dBA, I can just put the ECM8000 into the chamber and read the noise floor off my meter.


----------



## Anechoic

Sonic Icons said:


> Hi, I hope the following question for Herb isn't considered abusing a dead horse :time-out: (that has already been discussed extensively in the thread):
> 
> Can you comment, based on your measurements, on "typical" variation of the ECM-8000 frequency response between the horizontal (0 degree, on-axis) and vertical (90 degree, grazing incidence) orientation?


They say a picture is worth a thousand words, so here are plots from 6 random multi-angle measurements:










It looks like they all start to diverge around 2 kHz, which is consistent with the data you see from measurement mic vendors. 

I think you're correct that the angle difference from mic-to-mic is more consistent than the frequency response, but I haven't gotten around to actually comparing difference curves to verify that. The "x" factor is the positioning of the mic element in the capsule which I noticed seems to have an effect on the upper frequency response of these mics.


----------



## Terry McGee

Heh heh, just going back to that schematic of the ECM8000, we've had a couple of interpretations on it, I thought I could really helpfully confuse things by adding another!

My feeling is that the circuit as drawn is probably correct, even if confusing. I think that first transistor (immediately after the capsule) is just there for absolute phase reversal, to make the mic conform to the "positive pressure wave hits diaphragm causes positive voltage excursion at pin 2" standard. Without it, pin 2 would go negative when the positive pressure wave arrived. Not a problem with a single mic, but a trap if you have more than one.

That then raises the question of what the lower transistor of the output pair is doing. If the circuit is wired as shown, its base connects (via a dc isolating capacitor) to earth (follow it round - it's a rather confusing bit of schematic drawing). So with a grounded base, there can be no signal on its emitter feeding pin 3. So it's not there to provide a balanced output voltage. 

My guess is that it's there just to provide a guaranteed impedance balance to the real output on pin 2. So that any noise, hum, etc injected by way of cables passing by speaker amp transformers, lighting rigs, or even by way of a mic body in electrical contact with something nasty will be balanced out as well as the preamp's cmrr permits.

They could have achieved the same phase reversal without need for the extra stage by swapping XLR pins 2 and 3, but that would prevent people using the mic in unbalanced mode.

It would be easy to test my theory - there should be signal output on pin 2 only. Of course, we can't be sure that they haven't changed the circuit over time!

The treble rolloff provided by C1, the 3n3 capacitor across the capsule FET, is pretty brutal - I wonder what the the response would be like without it! Ultrasonic? If we ignore the FET for the moment, the combination of R1 and C1 would roll off at 6dB per octave from around 3KHz. If we assume the FET drain impedance is similar to R1, that would lift the start of the treble rolloff to around 6K. Presumably the capsule exhibits a serious resonance somewhere near the top of the audio spectrum and this heavy rolloff helps keep it under control. The economics of commercial electronics manufacture has always been a mystery to me - I wonder how much more you have to spend to get a capsule that doesn't need such aggressive EQ. Another dollar probably!

Looked at another way, you could probably get in there with a more tailored network of components and achieve a far better response before calibration. But hey, that would be overcapitalising (to use real estate language). And you'd probably need an electron microscope to deal with the size of the components.

Terry


----------



## brucek

> My guess is that it's there just to provide a guaranteed impedance balance to the real output on pin 2.


Perhaps, but there would have been a lot easier ways to do that.

Looking at it again, I suspect it's simply drawn wrong and that the first BC118 stage is not only acting as a high impedance buffer for the mic element, but also as a zero gain phase splitter. 

I edited the diagram (below) to show where C6 is likely connected to the emitter of BC118 and not to ground. Generally a phase splitter would have equal resistors on the collector and emitter, but they're close, and it's the only solution I could come up with.... 

brucek


----------



## Terry McGee

> Perhaps, but there would have been a lot easier ways to do that.


Yes, that is possibly a weakness in my hypothesis! Very thorough though - perhaps too thorough for a low price mic?



> Looking at it again, I suspect it's simply drawn wrong and that the first BC118 stage is not only acting as a high impedance buffer for the mic element, but also as a zero gain phase splitter.


It's not really acting as an impedance buffer - note the values of R4 and R10 (ignoring other components for the moment) are virtually the same. But that doesn't rule out your zero gain phase splitter interpretation.



> I edited the diagram (below) to show where C6 is likely connected to the emitter of BC118 and not to ground. Generally a phase splitter would have equal resistors on the collector and emitter, but they're close, and it's the only solution I could come up with....


Yeah, that would certainly work, and would seem to explain the carefully balanced back end better. I wouldn't be too worried about the 1k2 vs 1k discrepancy. It might have been empirically found to give better balance, or it could be another typo - for example how many 46K resistors (R3) have you come across? Presumably a 47k and a partially colour-blind technician!

On behalf of my hypothesis, we need to note that there is no real need to balance the output voltage of a microphone - it's not as if the enormous voltages concerned are going to make a nuisance of themselves in a jackfield (which is why we balance output voltages). So either of our interpretations will work fine). Yours will have 6dB more output, but if they wanted that they could have put some gain in that intermediate stage (but not if they wanted the phase shift needed in your interpretation). Mine will be less fussy about working into an unbalanced load, but most people needing 48V phantom power will be getting it from a balanced preamp.

I guess there's nothing for it, one of us is going to have to go in there to find out! Or at least check that there is output on both 2 & 3 (your interpretation) or on 2 only (my interpretation). I'll get to that and report back. I'd have to say, I suspect on the balance of probabilities that yours is more likely! 

I think the most remarkable element in the circuit is the enormous HF load represented by C1 across the FET. Like sending a boxer into a ring filled to head height with marshmallows! Hmmm, suddenly suspicious, could this be another typo? Perhaps not, given that the turnover frequency would appear to be consistent with the variable top-end boost shown in the various response graphs?

Good to talk audio circuits with you, brucek!

Terry


----------



## Terry McGee

Hmmm, not so easy to get inside. I whipped the three tiny screws off the base of mine and successfully withdrew the preamp board to the limits of the capsule wiring - only about 2" (50mm). The PCB is covered in shrinkwrap (a good precaution against anything touching the inside of the case). So, presumably unless you're willing to remove the capsule you can't get the preamp out, and even then you have to remove and replace the shrinkwrap to see anything. I think I'll take the other approach and see if there are levels on both pins 2 and 3. I have some work on a preamp coming up - that would be a good time to answer such a question.

Terry


----------



## Terry McGee

Good grief - I seem to be right! Unheard of! 

A couple of posts back, I conceded that brucek was probably right in assuming a drawing error in the ECM8000 circuit drawing shown previously. 

My attempts to look inside were thwarted by the PCB being shrouded in heatshrink. I finally got around to slapping a CRO across the output from my ECM8000, and could only find a signal on pin 2 of the XLR. There was no audio at all on pin 3.

Just to prove the CRO and probes were working OK, I put both probes on pin 2, both traces showed equal signal. Then put them both on pin 3. Neither trace showed a signal. Whichever probe was put on pin 2 showed signal, the other didn't. Not much scope for doubt there.

To be sure that the signal was real, I played flute, and could see the wavelengths change as I changed note. Definitely real.

Both pins show the presence of phantom power, slightly different at 35V and 30V. That implies currents around 2mA in each lead, so there's no question of the wiring being wrong, and 4mA total sounds pretty typical.

Can't see anywhere where I'm going wrong. Always possible I guess that there's something "wrong" with my mic. Perhaps someone else with an ECM8000 and a CRO would like to check their mic?

If it's true, it's not a big deal of course, for reasons I mentioned earlier - we don't need a balanced output voltage, as long as we have a balanced output impedance, so that a balanced mic preamp will phase out any hum pickup on the cable. 

So, until someone finds that they are getting signal on both pins 2 and 3, we can probably assume the circuit as originally written is correct! And that the careful duplication of the output stage is just for impedance balancing.

Terry


----------



## Anthony

What is a CRO? I could check mine if I knew what kind of tester that was. I have access to o-scopes, LCR's, and a really good Fluke multimeter at work.


----------



## brucek

> What is a CRO?


Cathode Ray oscilloscope.



> Not much scope for doubt there.


Pardon the pun.... 



> And that the careful duplication of the output stage is just for impedance balancing.


And the most important part of any balanced setup. It's responsible for the CMR - (as you know).

brucek


----------



## Terry McGee

Hi Anthony

Sorry about the "CRO" - as brucek has mentioned, it stands for Cathode Ray Oscilloscope. Shows you how old I am - in my days in electronics all CRO's were based on "cathode ray tubes" - essentially a small-screen TV tube with electrostatic steering rather than the magnetic steering used on TVs. Indeed in my early days, they were all tube. So I guess I should get with the times and call it a Scope.

Now, keep in mind if you take your mic to work, you'll need to give it some phantom power to operate. And you'll need to set the Scope channels to AC to avoid the traces being pushed off screen by the phantom voltage. Be careful not to short either pin to earth (um, ground!) - the sudden spike can be very hard on the preamp input devices. (They're designed to operate on a signal around 1mV and shorting a pin to earth will give it around 30,000 times that!)

But if you can, it would be great to be able to put the matter beyond doubt!

brucek mentions the CMR, or CMRR as we used to call it. In case that's not a familiar expression to some, it's the Common Mode Rejection Ratio - the ability of the system to reject common mode signals (such as hum picked up equally on both wires) in favour of differential mode signals (such as the audio which is transmitted on only one of the wires, or which is transmitted normally on one wire and in anti-phase, or "upside down", on the other). 

So the question we're investigating is which of those two options the ECM8000 uses.

Terry


----------



## WopOnTour

Hi 1st post (well besides the 5 pads) 
I just purchased one of these mics with a MIC-MATE USB adapter for phantom power
I wish to use it with TrueRTA to help setup some speakers
My question is - should keep the mic close to the USB adapter (with a short XLR patch cable) and run a long USB cable OR useshort USB and run a long XLR to the mic??
Thanks to any help
Regards
WopOnTour


----------



## Pete B

*ECM8000 Schematic*

This link to a schematic for he ECM8000 was posted by Shaun over at DIYaudio:
http://www.awdiy.com/uploads/pdf/Behringer_ECM8000_mic_schematic.pdf

Looks like there are a few errors as I commented in this post, anyone know the source of that schematic:
http://www.diyaudio.com/forums/multi-way/144306-diy-measurement-mic-7.html#post2013214

Not sure if there is a better place for this post.

Pete Basel


----------



## brucek

Pete, we've discussed this subject starting on page 4 and continuing on page 5 of this thread.

brucek


----------



## Pete B

They moved my post so I did not see this previously, took me a while to figure that out was wondering why I didn't see it before! LOL!
Well, measuring the mic is the sure way to figure out how it is wired but it really doesn't make any sense since they included the phase splitter as has been already mentioned. The resistors would be the same if Ic = Ie which is close, and true for infinite beta, but in real life Ie = Ic + Ib so Ie gets some "help" from the input signal and would require a slightly smaller resistor in the emitter path. Looks like they got them backwards. Perhaps they saw a mismatch in amplitude and just decided at the last minute to ground one side. Ran out of time or money in the budget to fix it - perhaps?

Thinking a bit more, even for a beta of 100, the emitter current is only 1% higher than the collector and there is no reason with 1% value resistors to make them different. Not sure why they did it - I'd guess that they chose the values more for what they thought would be good for DC biasing. Really, they both should have been 1K and the base bias resistors chosen for a good operating point.

Pete Basel


----------



## Pete B

Re: Terry post 102 above:
I recently purchased an ECM8000 and mine also only has output on one pin.


----------



## delphiplasma

Hi,

Just a quick query regarding the ECM8000. My ECM8000 came with a response curve, provided by the manufaturer. The response curve is to within 2db from 15hz to 20khz.
I've noticed that calibration files(provided onthis sie) and response curves, taken for the calibration files, show that the mike requires up to 5db correction, above frequencies of 2khz. This somewhat makes it seem no more accurate than a bog standard spl RS meter.However, it appears accurate at lower frequencies, better than the RS spl meter using the calibration files. My questions is, is the ECM8000 useable above 2khz, even with the calibration files?

Thanks

Delphi


----------



## Anechoic

delphiplasma said:


> Hi,
> 
> Just a quick query regarding the ECM8000. My ECM8000 came with a response curve, provided by the manufaturer. The response curve is to within 2db from 15hz to 20khz.


If you're talking about the curve on the box, that curve has no basis in reality. It may have at one time, but not anymore.



> I've noticed that calibration files(provided onthis sie) and response curves, taken for the calibration files, show that the mike requires up to 5db correction, above frequencies of 2khz. This somewhat makes it seem no more accurate than a bog standard spl RS meter.However, it appears accurate at lower frequencies, better than the RS spl meter using the calibration files. My questions is, is the ECM8000 useable above 2khz, even with the calibration files?


It's perfectly fine as long as you're using the calibration file and you're not trying to measure very high SPL's (over ~ 115 dB).


----------



## Wayne A. Pflughaupt

What Anechoic said. The graph you see on the ECM8000 box is useless. Here is a graph that shows the response of a few dozen mics as measured by Cross Spectrum. You can see that the deviations are pretty severe.










Regards,
Wayne


----------



## glaufman

I'll third what Anechoic said. But rather than use the curve on the box, you'll be better off using our generic cal file, or having Cross Spectrum created one for you based on your particular sample.


----------



## delphiplasma

Thanks for the responses. I did a comparison between the ecm8000 and my RS meter. The RS meter is pretty good. However, there is the typical 3 to 5 db increase from 3khz up to 8khz and a quick roll off after 10khz. This would lead me to believe that the ECM mic, is flat from around 40hz up to around 9khz. Above 9khz there would appear to be a dramatic increase of a few dbs up to around 20khz. I sent a question to Beringer (see below):

"My question is have you any calibration files? I have been advised that the microphone I purchased, 2-3 years ago does not have the linear frequency response curve as seen on the box, instead there is a rise in frequency from 2khz to a peak of 5db at 10khz. I've been told that the curve may have been accurate for microphones made when the response curve was taken. Therefore, is it possible for a re-test to be done on these microphones and a calibration file, or calibration details provided?"


Thanks for writing to BEHRINGER technical support.

"No, there are no other calibration files for the ECM8000. The users manual and what is on the box is all that is available for this. There have been no changes in production to the ECM8000 since its introduction. As these mics are manufactured in China, it is not possible to be sent back to the factory for a retest. You could always have a local service center, studio, or production company test the mic for you. Honestly, for the $40 dollar price of the ECM8000, it would be less expensive to buy a new one if your current one is no longer accurate.


We hope that we have been able to help you with this information"


----------



## Anechoic

delphiplasma said:


> There have been no changes in production to the ECM8000 since its introduction.


This is sheer fantasy, there are any number of sites that have documented changes in the capsule and pre-amp circuits of the ECM8000 over the years.


----------



## glaufman

And the bottom line is that our data on multiple ECM8000's say that some have a rise at HF and some drop off. Hence the desire to get a custom cal file generated if you're that concerned with accuracy.


----------



## counsil

When creating a sound card calibration file for my MobilePre, is it okay to use an XLR (using the XLR balanced in jack) to 1/4" (using the 1/4" unbalanced out jack) cable as long as I don't turn on the phantom power? Or should I use a 1/4" to 1/4" cable (which I currently don't own). I don't want to fry my MobilePre.


----------



## Wayne A. Pflughaupt

No, you have to use the 1/4" jacks only. The XLR jack puts the mic pre-amp in the loop, and that should be avoided because they're so sensative.

Regards,
Wayne


----------



## Anthony

I did it both ways to see if there was a difference. There was nothing major that I could see. A few little changes here and there, but tough to see. The mic cal is much more important. Images below:

Top one should be the Quarter to Mic. Bottom is Quarter to Quarter.

Quarter to quarter is easier and you can get the cable at any guitar shop (or Radio Shack)


----------



## counsil

Anthony said:


> Quarter to quarter is easier and you can get the cable at any guitar shop (or Radio Shack)


Thanks man. I think I saw some posts from you regarding all of this when I was researching the MobilePre. I thought you had to make a -30dB attenuator so the phantom power didn't hose your MobilePre?

Since I already have an XLR to 1/4" cable, can I go ahead and use it? I am assuming that the phantom power should be turned off so power won't go into the 1/4" input.


----------



## Anthony

The attenuator was to go between the mic level and the line level of the 1/4" plug. It was in no way a protection circuit. I have no idea what would happen if you turned on phantom power, but it might not be good :yikes:

I don't know enough about your mic to 1/4 adapter cable. Does it attenuate? Is it balanced to balanced (tip-ring-sleeve)? I still think 1/4 to 1/4 is easiest, but if you have the cable you should be able to try it. I would keep the levels and gains VERY low at first to make sure you aren't over-feeding it. It can protect from a serious clip, but only so much.

Good luck.


----------



## counsil

Here is the exact cable that I have...

http://www.amazon.com/gp/product/B002P9XCZY/ref=oss_product

Do you think it would be safe to use for calibration?


----------



## Anthony

It won't attenuate, but it is unbalanced, so the mic input should know what to do with it (i.e. go unbalanced for the input signal).

It's been a while since I did that experiment so I'll have to refresh my memory on what I did.


----------



## counsil

Anthony said:


> It won't attenuate, but it is unbalanced, so the mic input should know what to do with it (i.e. go unbalanced for the input signal).
> 
> It's been a while since I did that experiment so I'll have to refresh my memory on what I did.


I appreciate your help.


----------



## Anechoic

Anthony said:


> The attenuator was to go between the mic level and the line level of the 1/4" plug. It was in no way a protection circuit. I have no idea what would happen if you turned on phantom power, but it might not be good :yikes:
> 
> I don't know enough about your mic to 1/4 adapter cable. Does it attenuate? Is it balanced to balanced (tip-ring-sleeve)? I still think 1/4 to 1/4 is easiest, but if you have the cable you should be able to try it. I would keep the levels and gains VERY low at first to make sure you aren't over-feeding it. It can protect from a serious clip, but only so much.
> 
> Good luck.


I just had to mention that my niece saw your avatar, and now we're watching Ratatouille.


----------



## Anthony

Anechoic said:


> I just had to mention that my niece saw your avatar, and now we're watching Ratatouille.


I cook a lot in my spare time . . .


----------



## Anthony

Counsil,
I just reread this entire thread (it kinda took off on its own). Now that I remember stuff, I think the worry was that we couldn't get the level down low enough without the attenuator. But with the master volume low and the dial gain all the way down, you can slowly bring it up to see how it looks.

If it goes all over the place, or looks too different from the graphs I posted, you may have to either attenuate or just do the 1/4 to 1/4 calibration when you can get a cable.

Let us know how it goes.


----------



## counsil

Instead of getting the MobilePre, I am thinking of getting an M-Audio Fast Track Pro from a buddy of mine for really cheap (<$100). The Fast Track Pro has a mixing knob. Below is what the M-Audio website says about the knob. Where should I set it during sound card calibration and where should I set it when taking measurements? I have an XLR to 1/4" TRS cable (balanced to balanced) and an XLR to 1/4" mono (balanced to unbalanced). I would like to use one of them during the sound card calibration as I don't have a 1/4" to 1/4" cable. Thoughts? Same as above? Just turn the gain down really low to avoid clipping?

------ begin of quote --------

Q: What is the function of the Mix knob on my Fast Track USB/Podcast Factory USB/ Fast Track Pro?

A: The Mix knob on these devices controls the audio mix sent to select analog outputs, fading between the input signals from microphones, guitars, or other audio sources plugged into the device and the output signal from your audio application software. When turned fully counter-clockwise (input position), only the input signals from external sources are heard at the affected outputs of your device. When turned fully clockwise (playback position), only the output signal from your DAW software is heard at the device’s affected outputs.

Next to the Mix knob you will find a "stereo/mono" input selection button. If you are monitoring a mono input source (such as a guitar or microphone plugged directly into one input on your Fasttrack) you will need to have this button set to "mono" so that the mono input signal is panned to both your left and right speaker or headphone ear.

The outputs associated with the Mix knob are generally those that would be used to connect to a monitoring system like speakers or headphones. On the Fast Track USB and Podcast Factory USB, the outputs affected by the Mix knob are the red and white “1/L” and “2/R” outputs and the headphone output. On the Fast Track Pro, TRS outputs 1 and 2 (along with RCA/phono outputs 1 and 2) are affected by the Mix knob. 

The advantage of having this type of Mix control is that you can create your own monitoring mix between the external input being sent to your computer and the software output coming back from your computer’s recording/DAW software.

For example, if you were recording a live instrument track, and wanted to be able to hear other pre-recorded tracks in your project while you performed, you could set the mix knob halfway between Input and Playback. Setting the Mix knob halfway between Input and Playback would allow you to hear your instrument input (with zero latency) while recording, while allowing you to also listening to the other tracks playing back from your DAW at the same time. In many cases, “directly monitoring” your external input like this is preferable to relying on the signal coming back from your DAW software to provide you with live input monitoring, as the slight delay introduced by having to send the external input signal from your instrument to your computer/DAW then back to your audio interface can make it difficult to perform your music reliably. 

Lowering your latency/buffer settings for your hardware (when possible) can reduce the amount of delay inherent in monitoring your live input through your software, but the zero-latency monitoring offered via the Mix knob will always allow you to accurately and comfortably monitor your performance regardless of your hardware latency settings.

The Mix knob does not affect the signal being sent to your computer for recording in any way.

------ end of quote --------


----------



## Wayne A. Pflughaupt

> The Fast Track Pro has a mixing knob. Below is what the M-Audio website says about the knob. Where should I set it during sound card calibration and where should I set it when taking measurements?


Sounds like a monitoring function. I believe the full-clockwise position is what you want (input sources off).

Regards,
Wayne


----------



## charlesp210

Great dialog, but not clear to me if there is a conclusion wrt microphone angle, the original topic of discussion.

Is it fair to say the conclusion is now that ECM8000 microphone should be best pointed at speaker for full range measurements UNLESS you only have a calibration that was done otherwise? It sounded like Anechoic does calibrations at both 0 and 90 degrees. Does 0 degrees means pointed at speaker? 0 degrees seemed to show HF peak between 10k and 20k (2-10 dB, average around 5) but extended response to 20khz. 90 degrees (vertical) gives flatter response at first, then drops 10dB or so at 20khz.

But even if it is "best" it may not be worth the trouble, given you have vertical calibration it's far easier to do vertical orientation measurements (and particularly if you need to do several).

One problem might be if microphone becomes more orientation/position sensitive when pointed at speaker. Perhaps vertical orientation would reduce that, for one thing, there would be less issue regarding how exactly you are aiming it, and therefore more repeatable results. Plus, it would be a whole lot easier for measuring multiple channels to use vertical orientation.

Another question in my mind is "what does vertical mean"? Is vertical pointing at ceiling or pointing at floor?

Now a question no one has mentioned here. Is it better to measure with listening chair in position? It would seem to me better to remove listening chair from room, otherwise gating will be ineffective, lots of early reflections. Human listeners, from what little I understand, can to some degree compensate for the early reflections from something like chair.

And how about this question: if you choose to use just one capsule position or vertical orientation, what part of listener's head should microphone capsule be positioned at? It would seem to me that for best accuracy, left-side channels should have microphone capsule positioned at left ear (where it would be during listening), and vice versa. I don't think I've ever seen anyone do this. If you choose not to take the trouble to do it, would it be better to position capsule at nose position or midway between the ears?


----------



## Wayne A. Pflughaupt

Welcome to the Forum, Charles! These links should answer most of your mic orientation questions.

http://www.hometheatershack.com/forums/rew-forum/20293-full-range-eq-no-go-4.html#post184039
http://www.hometheatershack.com/forums/rew-forum/28299-first-time-rew-plot-3.html#post263849

There’s no good reason to get worked up about the listening-position furniture being in the room. The main thing is to keep the mic away from adjacent surfaces, especially the front and sides of the capsule. Just position the mic about a foot or so in front of where your head would be (i.e., giving it some distance from the back of the seat, especially if it’s high) and you’ll get good results.

Regards,
Wayne


----------



## BETO

Hey i dont speak english so much as you do.. But i have a question im new in this thing i cant get working the rew program.. Mi question is doews this program works with my mini laptop microphone? Because non sistem goes higher than 94 db or 98 db please help..


----------



## Wayne A. Pflughaupt

Hi Beto,

Any mic used with REW requires a calibration file. Without a calibration file, the measurements will not be accurate.

Regards,
Wayne


----------



## Rudy81

Just got a new, calibrated ECM8000 from Spectrum. I thought I'd ask a few, probably redundant, questions before taking some readings.

In particular, I wish to measure the performance of each of my drivers in my room, hence the problem. I don't have an anechoic chamber and taking the speakers outside is a no go due to their size.

I understand the best way to get a reasonable reading is to use the gating function to exclude room interaction. If that is correct, what are the recommendations for the gates? How far from the driver should the mic be placed? My speakers are two way DIY products with 15" ported bass bins and Tractrix horn HF.

If this has been covered in another thread, my apologies and could you post a link? I'm still searching.


----------



## Anthony

I used to do "Distance to first reflection point"/1100ft/s = Time to First reflection.

This is from memory, but I think that's right. Set the first gate to a few ms before the wave would even arrive (to minimize noise) and then the second gate after the first reflection.

For me, that was usually the floor and was really close, so I couldn't get any bass measurements. I would cover the floor with pillows and fluffy blankets and then use the next reflection (ceiling) measurement for the gate. This was for when I was getting measurments from the listening position.

For actual driver tests, I had a stick that was exactly 1m long that used to space the mic on axis at that distance. No early gate, but I set the late gate the same way as above.

If you can see the time/pulse waveform, you can actually see spikes when the first wave arrives plus all the reflections. This can give you a better idea of where to set the gates.

It's been a while, so this may be a bit rusty. Good luck, and let us know how it goes.


----------



## Rudy81

Anthony, thank you and I will post results when I get going on this. Likely sometime next week.


----------



## inspired

I've just purchased a pair of Behringer ECM-8000's that I will eventually have calibrated, but would like to download "Sonny's (Sonnie's?) calibration file" for some immediate measurements.

I've used the search function and can't seem to locate the Behringer ECM-8000 calibration file that I've seen mentioned in several threads here.

Where can I find it?


----------



## BETO

thnks for your help.. my computer fail ad until ow i got it workimg.. im trying to use the rew program for car audio..:T i don´t know where to find a mic for made my mini lap acer workig:scratch:.. can you please tel me where to uy one ad send it here to mexico? im triying to get my self into the spl compaddle:..:clap: as you know im new in this.. thnks so much for your :help:..:wave:


----------



## LastButNotLeast

inspired said:


> I've just purchased a pair of Behringer ECM-8000's that I will eventually have calibrated, but would like to download "Sonny's (Sonnie's?) calibration file" for some immediate measurements.
> 
> I've used the search function and can't seem to locate the Behringer ECM-8000 calibration file that I've seen mentioned in several threads here.
> 
> Where can I find it?


http://www.hometheatershack.com/forums/downloads-area/19-downloads-page.html


----------



## inspired

LastButNotLeast said:


> http://www.hometheatershack.com/forums/downloads-area/19-downloads-page.html


Thanks LastButNotLeast, I ended up muddling around the site last month when I posted this and finding that link.

I've ended up with 2 of the ECM8000's that I've had professionally calibrated, 2 boom stands and an Alesis iO2 USB interface. I'm experimenting with ARTA, REWv.5, TrueRTA and ETFv.5 software.

I do a bit of speaker modding as well as solving mode problems, and with 2 mics I'm able to take Stereo Listening Position measurments as well as standard Nearfield and 1Meter/1Watt measurements. I'm having a blast experimenting with this gear and am really pleased with the cost/performance ratio.


----------



## VictorM

Great thread! Just got myself an ECM8000, I can't wait to start measuring!


----------



## BETO

hi im looking for a mic for a mini lap acer.. im trying to use it in car audio.. i live in mexico and my lap burns when i try to use it with the mic it has... but then i read i cant use it with it... so i need one.. has anyone a mic it wont use anymore?.. i cant pay much for it.. but if you tell me how much i save the money to get it... thnks..


----------



## Wayne A. Pflughaupt

Hi Beto,

The only cheap mic that can be used with REW (assuming that’s what you want it for) is the Radio Shack SPL meter. If your computer has a line input. If it doesn’t you’ll also need a USB sound card.

But the Radio Shack meter is only good for low frequency (subwoofer) measurements. If you want full range measurements, there is no cheap option. Even if you use our generic calibration file, the ECM8000 mic with a suitable sound card that has a pre-amp and phantom power will cost at least $100.

Regards,
Wayne


----------



## BETO

Hi again.. thanks for the info.. look i dont know english so much but i just read abouot be a moderator.. what this mean? i dont under stand.. besides..how can i help you if you are kings in this work? you are the bible fro all knowlege.. i dont even know how to fix my pc.. or how to calibrate a car.. sorry i cant help you because i dont know all you do know.. thnks..


----------



## Wull

What happens if you use the ECM8000 Basic Mic 'not Basic +' with Cal file for measuring your rooms response?


----------



## Wayne A. Pflughaupt

The Basic + adds calibration for 45° and 90° mic orientations, in addition to the 0° orientation of the Basic calibration package. However, for frequency response measurements you typically want 0° orientation – i.e., pointed at the signal source. More reading as to the “whys” and “wherefores” here.

Regards,
Wayne


----------



## Wull

Wayne A. Pflughaupt said:


> The Basic + adds calibration for 45° and 90° mic orientations, in addition to the 0° orientation of the Basic calibration package. However, for frequency response measurements you typically want 0° orientation – i.e., pointed at the signal source. More reading as to the “whys” and “wherefores” here.
> 
> Regards,
> Wayne


Thanks Wayne.

The more you go into EQ the deeper it gets that's for sure, it's like, just as you learn how to open one door another comes along with a bigger lock, 'so to speak'. 



*The short answer for subwoofer measurements is, it doesn’t matter. 

If you’re doing full-range measurements (your main-channel speakers), the short answer is, you only point the mic towards the ceiling if you’re using a 90-degree incident (vertical) calibration file.

Horizontal orientation with the mic on-axis to the sound source (0-degrees incident) has been the traditional method for full-range, free-field measurement, where the room was an open space relatively free of reflections. However, that’s mainly because most stand-alone RTAs (which until several years ago was about the only thing available) came with mics that were calibrated for on-axis measurements.

Some RTA manufacturers offered the option of 90-degree orientation for random incident measurements (aka diffuse field), where the sound arrives from all directions more or less simultaneously, with equal probability and level. In other words, an exceedingly reverberant environment. Random-incident measurements required a different capsule for the measurement mic (which the manufacturer made available), for reason of the specific calibration as well as a housing better suited for 90-degree orientation. 

That just refers to the mic’s position during its calibration, however. Everything I’ve seen for actual “in the field” measurements says the standard protocol for horizontal (on-axis) measuring is 20 degrees, and 70 degrees for vertical (i.e., angled slightly forwards towards the sound source). This may have something to do with compensating for interference from the mic’s housing with the sound waves, I forget exactly why. 

The ready availability these days of mics with 90-degree calibration certainly opens up more measurement options. Others have their opinions, and maybe they’ll weigh in, but mine is that you will generally get the best results with on-axis measurements. It should be a no brainer to figure out that the home theater environment, while certainly not totally free of reflections and reverberation, more closely resembles a free-field environment than a random-incident environment. 

Vertical orientation may add more upper-frequency information from ceiling reflections than you’d get with on-axis, and as such will probably influence what the RTA displays. How much so will depend on your particular room – how “live” it is, the height of the ceiling in relation to the distance between the sound source (speaker) and measurement mic (i.e. inside or outside the “first reflection” zone), etc. Even though the ECM8000 is omnidirectional, its capsule is rather large for a measurement mic. As a result, its off-axis response (compared to on-axis) starts skewing as low as 3 kHz. So differences >3 kHz are what you might see with horizontal vs. vertical readings. (Smaller-capsule omni mics typically retain uniform 0 vs. 90-degree response at least an octave higher.)

Regards,
Wayne*


----------



## Wull

Hi.

I have just received my ECM800 'Basic' Mic from Cross Spectrum. It comes with two Mic Cal files. I was wandering which Cal file I load into REW, either the 'narrow band response 0 degree', or the 'one third octave band response 0 degree'.
:scratch:


----------



## Wayne A. Pflughaupt

There should have been a “Read me” file on the calibration disc that includes the following:



> The narrow-band-response.FRD files are designed for use with measurement and analysis programs like Room EQ Wizard, ARTA, and FuzzMeasure Pro that can make use of fine-tuned correction curves. The one-third-octave-response.FRD files are designed for applications where additional smoothing is warranted or for comparision with criteria given in terms of 1/3-octave bands.


Regards,
Wayne


----------



## Wull

Wayne A. Pflughaupt said:


> There should have been a “Read me” file on the calibration disc that includes the following:
> 
> 
> 
> Regards,
> Wayne


Thanks Wayne, this is what mine reads:

Frequency Response Files:
The narrow band response x degree.FRD files contain the narrowband (FFT) frequency response response
calibration files for the microphone at an angle of 0 degree incidence (microphone pointed directly at the sound
source), 45 degrees incidence (microphone pointed diagonally with respect to the sound propagation path of the
source) and 90 degrees incidence (microphone perpendicular to the sound propagation path of the source).

The one third octave band response x degree.FRD files contain the one-third octave band frequency response
response calibration files for the microphone at an angle of 0 degree incidence (microphone pointed
directly at the sound source), 45 degrees incidence (microphone pointed diagonally with respect to the sound
propagation path of the source) and 90 degrees incidence (microphone perpendicular to the sound propagation
path of the source).
P.


----------



## Anechoic

Wull said:


> Thanks Wayne, this is what mine reads:
> 
> Frequency Response Files:
> The narrow band response x degree.FRD files contain the narrowband (FFT) frequency response response
> calibration files for the microphone at an angle of 0 degree incidence (microphone pointed directly at the sound
> source), 45 degrees incidence (microphone pointed diagonally with respect to the sound propagation path of the
> source) and 90 degrees incidence (microphone perpendicular to the sound propagation path of the source).
> 
> The one third octave band response x degree.FRD files contain the one-third octave band frequency response
> response calibration files for the microphone at an angle of 0 degree incidence (microphone pointed
> directly at the sound source), 45 degrees incidence (microphone pointed diagonally with respect to the sound
> propagation path of the source) and 90 degrees incidence (microphone perpendicular to the sound propagation
> path of the source).
> P.


The part Wayne quoted is on Page 2.


----------



## Wull

Anechoic said:


> The part Wayne quoted is on Page 2.


:doh:

Sorry to continue sounding thick:

So in the REW/Preferences/Analysis

When running REW with no smoothing then use 'The narrow band response'

And use the one third octave band response when applying only the 1/3rd. What about the other smoothing frequency responces?


----------



## Anechoic

Wull said:


> :doh:
> 
> Sorry to continue sounding thick:
> 
> So in the REW/Preferences/Analysis
> 
> When running REW with no smoothing then use 'The narrow band response'
> 
> And use the one third octave band response when applying only the 1/3rd. What about the other smoothing frequency responces?


For REW, just use the narrow band correction curve, no matter the smoothing you're using.


----------



## Wull

Anechoic said:


> For REW, just use the narrow band correction curve, no matter the smoothing you're using.


Thanks :T


----------



## kipsus

Hi guys,

I don't know if this has been discussed before (not that I haven't searched) but in my quest in finding an affordable and convenient microphone calibration (by substitution) solution I stumbled across this:
















(I don't know why the images are not showing up, maybe it's the forum censorship, just do a google on "rockwool tube")
It's rockwool tube used for plumbing purposes, it can be acquired in all kinds of thickness, diameter, density, with or without the foil shell. The idea is that it can be used as a anechoic chamber for high frequencies (best case scenario 1kHz and up) between the tweeter and the microphone.

Now while this is obviously an anechoic "chamber" at certain frequencies, the fact that it's quite narrow will inevitably affect the frequency response (some sort of high-pass filter?). On the positive side, reflections may get attenuated, compared to free air measurements, resulting in smoother overall response.

Also, correct me if I'm wrong but a very reliable and precise method of low end calibration should be nearfield measurement, as described in Claudio *****'s page.

Any comments appreciated
K.


----------



## Wull

Hi.

Is there a Generic Cal file available for the ECM8000 Mic for 90 degree orientation?


----------



## THX-UltraII

My Cross Spectrum ''Basic Plus'' ECM8000 will arrive next week. I want to make measurements with this mic+REW+my Tascam 122 MKII. Can you guys tell me what I need to do FIRST with the ECM8000 before I can start making measurements? I only know that I will need to plug in the ECM8000 to the L or R xlr input of my Tascam 122 MKII but that s all I know 

Thanks guys!


----------



## Wayne A. Pflughaupt

The first thing you'll need to do is copy the calibration files from the disc that will come with the mic to the REW Calibration Files folder on your computer. Then, open REW and go to Preferences/Mic-Meter and open the "narrow_band_response_0_degree.cal" file.

If you're still lost at this point, then you obviously haven't studied the Help Files. 

Regards,
Wayne


----------



## THX-UltraII

Allright. This seems simple enough! thxz


----------



## THX-UltraII

Wayne,

where are the other calibration files are for and why do I have to use the ''narrow_band_response_0_degree.cal'' file?


----------



## Wayne A. Pflughaupt

Not sure if you’re asking why you should use the narrow-band file vs. the third-octave, or why use the 0° file vs. some other?

Zero degree is the only orientation file type you’ll have unless you bought one of the upgraded calibration packages. If you did, there would also be 45° and/or 90° calibration files as well. I believe we’ve already discussed why 0° is preferable over the others, right? 
If it’s the narrow band file vs. the third-octave that you’re wondering about, Herb covered that at Post #154.

Regards, 
Wayne


----------



## THX-UltraII

thxz again for always your quick response Wayne.

Ok, so always use the narrow band response. CHECK!

But can you tell me where it is discussed why 0 degrees is the one to use?

(ps. I indeed have the version with 0, 45 and 90 degrees files)


----------



## Anthony

What are you measuring? If you are measuring full range speaker response then the mic should be pointed at the test subject directly (0 deg). This is the only way to get accurate upper mid and high frequency measurements.

If you are measuring bass response of a room at the listening position, then an indirect reading is preferable (mic pointed straight up, 90 deg)

I haven't ever used the 45 deg alignment, but I imagine it could be useful for getting a hybrid measurement of both with the same sweep.


----------



## THX-UltraII

I want to measure full range from 0-20000Hz for both my subwoofer and main speakers at the same measurement. Is that possible with REW?


----------



## Sam Ash

*ECM 8000 & MacBook Pro - Request for assistance*

I'm hoping someone here can give me some help. I am interested in learning how to use REW and need to invest in a microphone. The Behringer ECM8000 seems to be a good starting point but currently I am using an older generation MacBook Pro (2.16 Ghz Intel Core Duo) running Mac OS X 10.5.8. I checked the manual to establish the spec on the internal sound card and audio interfaces on my system and this is what it says:-

_An audio line in/optical digital audio in port and a headphone/optical digital audio out port for connecting headphones, speakers, microphones, and digital audio equipment.

You can connect external speakers, headphones, 5.1 surround systems, and other sound output devices to the headphone (f) port. The headphone port is also a S/PDIF stereo 3.5 mini-phono jack. When devices are plugged in, sound won’t come through your built-in speakers. Unplug any headphones or speakers to hear the computer
speakers.

You can also connect external microphones or other audio equipment to the audio line in port. The audio line in port is also a S/PDIF stereo 3.5 mini-phono jack, which does not provide power to a connected device, so you must use self-powered peripherals. Using a Toslink jack-to-miniplug adapter, you can use a Toslink cable to connect Digital Audio Tape (DAT) decks or digital instruments to input and mix your own music._

Questions:-

1. Is the sound card in my machine good enough ?

2. Is it better to get an external preamp/amp with the ECM8000 ?

3. What cables do I need considering that my main interest in REW is to use it to optimise my home theatre system.

4. I am interested in an easy workflow - e.g. long cables so that I can manoeuvre the mic without having to move my computer with it.

5. Are the ECM8000 calibration files available from the REW site accurate enough to avoid paying the extra amount for a dedicated calibration ?

6. Is the Mac Version of REW 5 just as good as the PC version ?

A comprehensive answer from a Mac user or otherwise will be appreciated as I would like to buy the right stuff from the very start. A kind friend on the forum has offered to help me to learn REW but he uses a PC and Windows OS and I can only start once I have all the right gear.

Cheers,

Sam


----------



## Wayne A. Pflughaupt

THX-UltraII said:


> thxz again for always your quick response Wayne.
> 
> But can you tell me where it is discussed why 0 degrees is the one to use?


My apologies, I confused you with someone else.  Here ya go:

http://www.hometheatershack.com/for...dio-calibration-file-mike-use.html#post532024

Regards,
Wayne


----------



## MANAGER

hi i'm new here, but i'd like to know more about the ECM8000. I'm going to buy it but i'm not sure for the price/quality... you guys maybe could help me! there is a similar price mic with better quality?

thank you!
Marco


----------



## Phillips

MANAGER said:


> hi i'm new here, but i'd like to know more about the ECM8000. I'm going to buy it but i'm not sure for the price/quality... you guys maybe could help me! there is a similar price mic with better quality?
> 
> thank you!
> Marco


Welcome

1. Deal with Herb from Cross - Spectrum if you can, here is his thread click here http://www.hometheatershack.com/for...ctrum-microphone-calibration-service-usa.html

2. Purchase a calibrated mic


----------



## sledge

Hi Guys. 
I did some measurement of five ECM 8000 units in vertical and horizontal possition and I think it might be helpful to see responses from different mics:
Horizontal responses rel. to beyer MM1:
 

Vertical responses rel. to beyer MM1 (MM1 stays horizontal):


PS: The absolute level of SPL does not match between those pictures (levels bellow 1 kHz should match on each color)


----------

