# Full System Calibration - Choosing & Setting Up a Microphone



## Stoopalini (Sep 30, 2014)

I'm looking to do a full system calibration, ie: set EQ curves of each speaker independently, and am gathering information to help me do it correctly.

I am using a Tascam US-122 external USB sound card, which has both 1/4" and XLR inputs. It also has phantom power ability.

As far as I can tell, the major, high level, steps are:

Connect appropriate hardware and test the input/output functionality
Loop the output of the sound card to the input, and perform a REW calibration of the sound card
Load a calibration file for the mic I am using
Calibrate REW's SPL meter to the mic's measurement of SPL at the measurement position
Connect the sound card's output to the amplifier section of the speaker I wish to calibrate and perform a measurement
Compare measurement to desired response curve, and generate the PEQ settings for that channel

Does this look right?

The question I have right now is related to the calibration file for the microphone. I have a Radio Shack 33-2055 SPL meter, and also have a PreSonus PRM1 calibration mic. From what I am reading, the Radio Shack mic works well for sub calibration, but does not work well for full range calibration due to a drop off above 3khz. The PRM1 requires phantom power, and i use this mic for large venue calibrations, as I'm a musician and often assist the tech folks in getting the sound right in various rooms.

I cannot find a calibration file specific to the 33-2055 mic, and also cannot find one specifically for the PRM1 mic. Although the PRM1 mic is supposed to have a completely flat response curve from 20hz - 20khz.



PreSonus Documentation said:


> This mic can handle up to 132 dB SPL and exhibits linear (“flat”) frequency response between 20 Hz and 20 kHz, so it won’t color the sound.


So my questions are:

If I use the PRM1, how do I calibrate REW's SPL meter, as I won't have a reference of SPL from the mic itself. Can I just place the Radio Shack meter next to the PRM1 and use the readout from it to input into REW? I wouldn't think so, as the SPL calibration would then be based on the Radio Shack's mic and not the PRM1. Is this even a critical step to getting proper PEQ correction measurements?
Can I just use the Radio Shack meter's mic, and assuming a calibration file (which I have yet to find) does exist, it will provide compensation for any coloring, therefore allowing me to do full range measurements with this mic?
Is there a way to create a calibration file manually for microphones which do not have one offered by the manufacturer?

I'm sure I will have more questions as I go along, but this is where I am right now. Any assistance would be greatly appreciated.

________________________________________________________________

Since I can't seem to figure out a way to create a signature, or show my equipment list in the post, here is what my system consists of:

PROCESSOR
Emotiva UMC-200

AMPLIFIERS
JBL Performance AVA7 Amplifier (mains, center, rears)
Adcom GFA-545 Amplifier (front heights)
Carver a-400x Amplifier (subwoofer)
Mitsubishi DA-A10 (currently not in use)

SPEAKERS
2 - NHT vt-1.2a mains (bi-amped with 4 channels of the AVA7)
1 - NHT vs-1.2a center
4 - NHT Superones for rears and front heights
1 - DIY DVC Shiva Sonotube Subwoofer

DISPLAYS
Vizio M602i LED TV
Dell 5100MP DLP projector
Favi 120" motorized screen

SOURCES
Playstation 3 (BD player)
Original Wii
Dish Network VIP-722k
Apple TV 3


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## Wayne A. Pflughaupt (Apr 13, 2006)

Stoopalini said:


> As far as I can tell, the major, high level, steps are:
> 
> Connect appropriate hardware and test the input/output functionality
> *Loop the output of the sound card to the input, and perform a REW calibration of the sound card*
> ...


That’s right, but you can skip the second step. The TASCAM has ruler-flat response, no calibration file is needed. 

One thing you didn’t mention is measurement technique. The mic should be pointed at the speaker being measured. 

When equalizing the front L/R stereo pair of speakers, you should use matching filters for frequencies above ~3-400 Hz. A number of Forum members report that using independent filters above that range tends to do strange things to imaging. Below 3-400 Hz separate filters can be used. This is only an issue with the front stereo pair, not the center or surround speakers; they can be equalized as needed.

Since you appear to be new to full-range measurement, here’s some recommended reading.

Minimal EQ (at least the first two posts)
House Curve
Full Range EQ: A Case Study
Mic Orientation when Measuring
 Case Study: Problems Displayed with Vertical Mic Orientation
 EQ Boosting Vs. Cutting 
Equalizing Nulls




> The question I have right now is related to the calibration file for the microphone. I have a Radio Shack 33-2055 SPL meter, and also have a PreSonus PRM1 calibration mic.
> I cannot find a calibration file specific to the 33-2055 mic, and also cannot find one specifically for the PRM1 mic. Although the PRM1 mic is supposed to have a completely flat response curve from 20hz - 20khz.


The Earthworks M30 is an excellent measurement mic known to have verifiable flat response, and it cost nearly $700. The Presonus mic only costs about $100, so I would have my doubts as to how accurate it really is. Most of these mics use off-the-shelf capsules which typically vary from one sample to the next.

Bottom line, if you’re serious about full-range EQ you need to get a calibrated mic. How can you accurately equalize your speakers if you’re working from an inaccurate graph? You can get a calibrated mic from Cross Spectrum for under $100 – a bargain if there ever was one.




> Is there a way to create a calibration file manually for microphones which do not have one offered by the manufacturer?


How to Create a Mic Calibration File . Keep in mind that this is not a substitute for a calibrated mic because (as noted) a mic’s actual response can deviate from one sample to the next.




> So my questions are:
> 
> If I use the PRM1, how do I calibrate REW's SPL meter, as I won't have a reference of SPL from the mic itself.


One has nothing to do with the other. You use the SPL meter to calibrate REW’s internal meter, then use the mic for measurements. 




> Since I can't seem to figure out a way to create a signature, or show my equipment list in the post, here is what my system consists of:


Look at the top of the page for the “User CP” (control panel) button. You’ll find signature editing listed in the drop-down box.

Hope this helps! :T

Regards, 
Wayne


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## Stoopalini (Sep 30, 2014)

Wayne A. Pflughaupt said:


> That’s right, but you can skip the second step. The TASCAM has ruler-flat response, no calibration file is needed.


I did notice the calibration curve after doing the sound card test looked great. 



Wayne A. Pflughaupt said:


> One thing you didn’t mention is measurement technique. The mic should be pointed at the speaker being measured.


Right, sorry about that. I saw a post by Herb elsewhere in the forum where it was recommended to do measurements with the mic in the listening position and pointed 10-20 degrees angled down from verticle, towards the speaker. This is what I did. Should I retake the measurements with the mic pointed directly at the speaker drivers?



Wayne A. Pflughaupt said:


> When equalizing the front L/R stereo pair of speakers, you should use matching filters for frequencies above ~3-400 Hz. A number of Forum members report that using independent filters above that range tends to do strange things to imaging. Below 3-400 Hz separate filters can be used. This is only an issue with the front stereo pair, not the center or surround speakers; they can be equalized as needed.


I did read about this issue. Is it a viable measuring technique to have both the right and left mains play the sweep simultaneously while taking the measurements? Maybe run them from 400hz up to 20khz simultaneously, and apply those PEQ settings to both. then run them again, individually, with a 20hz - 400hz sweep?



Wayne A. Pflughaupt said:


> Since you appear to be new to full-range measurement, here’s some recommended reading.
> 
> Minimal EQ (at least the first two posts)
> House Curve
> ...


Great stuff. I am new to performing measurements like this on my home theater, although not new to sound system calibrations. I've calibrated some rather large venue, full range, systems ... hence the PRM1 microphone. I usually use SMAART though, which is integrated into the hardware I use. 

Thanks for the articles, I did not read them all yet, but agree with what I've seen thus far. When it comes to EQ'ing, less is definitely preferable, as well as reductions over increases. Most people who have experience with GEQs, who start using PEQs, don't realize how powerful a PEQ really is. In my large venue setup I have 8 assignable 31 band GEQs, and one 3-band PEQ per bus (and per channel); and I mainly use the bus PEQs only for room correction, leaving the GEQs off. 

Before I saw your post here, I had taken measurements of each speaker already. I used 1/6 smoothing and ran the sweeps on the sub from 20hz - 120hz, and sweep on the mains from 80hz - 20khz. I did my measurements connected directly to the amplifiers, but have the UMC-200 bass management setup with a 100hz crossover at 24dB. I'm not sure yet if this will cause unwanted increase in the crossover range, but will find out tonight. 

I also moved the target line to cross through the center of the natural curve; then let REW do it's auto-thing to suggest PEQ bands for compensation. For the sub and center, 75dB was perfect. For the mains and rears, 73dB was right, and for the front heights, 70dB placed the target in the middle. Your thought on using a hard knee curve is a good one, and I hadn't considered that before setting off to do my measurements. I'll have to do some critical listening and may take the measurements again implementing your idea.



Wayne A. Pflughaupt said:


> The Earthworks M30 is an excellent measurement mic known to have verifiable flat response, and it cost nearly $700. The Presonus mic only costs about $100, so I would have my doubts as to how accurate it really is. Most of these mics use off-the-shelf capsules which typically vary from one sample to the next.


Agreed; although my experience with the PreSonus mic has been very good thus far. It would be interesting to get a calibration chart on it ... I just may send it off to satisfy my curiousity.



Wayne A. Pflughaupt said:


> Bottom line, if you’re serious about full-range EQ you need to get a calibrated mic. How can you accurately equalize your speakers if you’re working from an inaccurate graph? You can get a calibrated mic from Cross Spectrum for under $100 – a bargain if there ever was one.


Thanks for the suggestion. I may do just that and compare the measurement curves between the two mics instead of sending the PreSonus off. 



Wayne A. Pflughaupt said:


> One has nothing to do with the other. You use the SPL meter to calibrate REW’s internal meter, then use the mic for measurements.


Thanks, this was my suspicion. The SPL level should not have an impact on the curve measurements, but I wanted to be sure the software wasn't using the dB levels in some unknown calculation behind the scenes.



Wayne A. Pflughaupt said:


> Look at the top of the page for the “User CP” (control panel) button. You’ll find signature editing listed in the drop-down box.


Funny enough, the Edit Signature option wasn't there when I looked previously, but it is now. The option for a custom avatar wasn't there either, but is now. It must have something to do with post count maybe?



Wayne A. Pflughaupt said:


> Hope this helps! :T
> 
> Regards,
> Wayne


Yes, it helps greatly! Thanks for taking the time to help me out, I do appreciate it!


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## Wayne A. Pflughaupt (Apr 13, 2006)

Stoopalini said:


> Right, sorry about that. I saw a post by Herb elsewhere in the forum where it was recommended to do measurements with the mic in the listening position and pointed 10-20 degrees angled down from verticle, towards the speaker. This is what I did. Should I retake the measurements with the mic pointed directly at the speaker drivers?


Can’t say that I’ve seen that one, but a few years ago I did start a recommendation to measure with the mic angled 10-20 degrees upward. It was based on info that I’d seen from the manufacturers of hardware RTAs (which were prevalent before the days of computer-based systems). I think it had something to do with diffraction or some other effect of the soundwave hitting the mic capsule, that could affect measurements. Regardless, we’ve had people take measurements both ways (I think jtalden?) - angled up slightly and straight-on – and reported they couldn’t see a difference. So, no reason to re-measure just for that.




> I did read about this issue. Is it a viable measuring technique to have both the right and left mains play the sweep simultaneously while taking the measurements? Maybe run them from 400hz up to 20khz simultaneously, and apply those PEQ settings to both. then run them again, individually, with a 20hz - 400hz sweep?


Many around here (including some of the more respected folks) say taking mains measurements with both speakers running will get undue comb filtering, due to the fact that it’s virtually impossible to perfectly center the mic between the speakers, and thus the measurement will be skewed.

My feeling of late is that unless your room is an anechoic chamber, you’re getting tons more comb filtering from reflections in the room than you’ll ever get from the mic not being perfectly centered. Considering that typical residential room reflections are in the 5-10 millisecond range - which roughly means that the reflected sound takes a path to the ear or measurement mic that is 5-10 feet longer than the direct sound – we can see that any comb filtering introduced by mic being off an inch or so is insignificant. And besides, that's what the smoothing function is for, to minimize the comb filtering so we can see the underlying trend in response.

So yes I think your approach for measurement and EQ would be a good one.




> Thanks, this was my suspicion. The SPL level should not have an impact on the curve measurements, but I wanted to be sure the software wasn't using the dB levels in some unknown calculation behind the scenes.


AKAIK it isn’t. We typically tell folks all the time that they don’t really need the SPL meter to take measurements; even JohnM (REW author) has stated that. :T




> Funny enough, the Edit Signature option wasn't there when I looked previously, but it is now. The option for a custom avatar wasn't there either, but is now. It must have something to do with post count maybe?


Probably so. Love your avatar, by the way. What Gibson model is that? 

Regards, 
Wayne


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## Stoopalini (Sep 30, 2014)

Thanks Wayne. I ended up running a sweep with both mains connected, and got the following results. 










This actually looks good to me. Even REW only suggested one PEQ at 127hz with a -14.25 gain and Q of 18 ... This was after I moved the target dB to 70.

I also ran a sweep with both the mains and the sub running, and got some significant cancellations in the room. I started another thread on this and see you've replied to that one already 



Wayne A. Pflughaupt said:


> Love your avatar, by the way. What Gibson model is that?


That's the headstock from my primary guitar. It's a 1978 Gibson Les Paul 25/50 anniversary edition. It's a heavy beast, but it's so solid and has "sustain for days"!  I swapped the pups with some Lindy Fralin Unbuckers, and since then, I rarely pick up any of my others.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Wow, that is one sweet guitar, thanks for sharing! Can’t say I’ve ever seen another Les Paul that color.

Regards,
Wayne


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## Stoopalini (Sep 30, 2014)

Ya, it's certainly a beauty! I bought it out of a collection I cataloged for a friend who wants to sell the pieces off. The original collection owner didn't play guitar, and bought this one in 1978, then passed away in 1980; so it was sitting in climate controlled storage since 1980. I was the 1st one to play it, and have all the original case candy, including purchase receipts, warranty registration card, etc ... It's very versatile, although last night I broke out my Telecaster for the first time in a couple of years for a particular song ... no matter how great the LP is, some songs just need that "tele quack" .... and effects are no substitute 

The collection has all sorts of gems in it (45 pieces in total), including a 1965 Fender P-bass and a 1962 Fender VI ... It was a complete JOY to be able to go through each piece and catalog them. Selling them has been a bit more challenging though ...

To add something valuable for the topic at hand: I contacted PreSonus support and asked for a factory calibration file for the PRM1 microphone. They don't have one, but put in an order for their lab to create one. I'm told it will happen, but they're not sure when.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Stoopalini said:


> ...last night I broke out my Telecaster for the first time in a couple of years for a particular song ... no matter how great the LP is, some songs just need that "tele quack" .... and effects are no substitute


 I hear ya! Personally I’m more of a Tele / Strat fan than LP myself, especially when played clean. :T




> The collection has all sorts of gems in it (45 pieces in total), including a 1965 Fender P-bass and a 1962 Fender VI ... It was a complete JOY to be able to go through each piece and catalog them. Selling them has been a bit more challenging though ...


Wow, very cool! I see you’re not that far from me, might be worth a drive to check it out!

Regards, 
Wayne


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## Stoopalini (Sep 30, 2014)

Ya, my tele was my primary guitar for a long time. It's a 2005 highway 1, which I modified with a center pickup buried under the pickguard and a 5-way switch installed 

There are certainly some nice pieces in this collection (1957 Telecaster, '57 junior, '64 Firebird V, 3 custom Erlewine built guitars, 1938 Super 400, 1960 Bassman amp) among many others. I can shoot you a spreadsheet with links to images if you're really interested?


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## Wayne A. Pflughaupt (Apr 13, 2006)

That would be awesome! Shoot me a PM and I'll send you my e-mail address. :T

Regards,
Wayne


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