# 3 way speaker measurements inside, outside & group delay: am I right?



## stonemarten (Jan 4, 2016)

Dear experts,

I did my first measurement of my speaker and need your review for understand if I'm right and I can proceed to model the crossover
Any comments on the response overall are welcome as well 
Mic: UMIK 1, at 1.5 meter, inside, 76 dB measured on the tweeter axis (no mic movement later, 10 measurements average). All .mdat files are available

Based on the impulse response, I take 2.5ms as gating window: is that correct? This is my main question, really not sure if it's right... I follow (I think...) the instruction in the MiniDSP site but would be sure I got it.
In my understanding, that window allow me to have a "pure" measurement until ~400 Hz, so can have the real behaviour of my speaker: am I correct? The response looks like a little bit flat to me, but again not sure if I'm right

Can I use REW to understand the group delay? the configuration is MTMWW and I understand that I need to run the 2 mids as one driver for calculate the delay. In case I can't do with REW, can I import the results directly in Win PCD or do I need to extract the minimum phase?

Tweeter on axis 














Mids on axis 














Woofer on axis 














Woofer2 on axis


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## stonemarten (Jan 4, 2016)

Tweeter 15 deg














Mids 15 deg














Woofer 15 deg














Woofer 2 15 deg


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## stonemarten (Jan 4, 2016)

These are the measurements of the woofers outside, on axis. I can't find the impulse feedback, and I used a 10ms gating window. Is that right? Can I expand it? What do you think about the response?
Both are at 1.5 mt. I have the 2 mt as well

Woofer 1 














Woofer 2














Thanks!!!


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## jtalden (Mar 12, 2009)

stonemarten said:


> Any comments on the response overall are welcome as well


The TW and MR responses look very good. It is more standard however to plot the SPL with 5dB gridlines. A 10dB grid soothes the appearance a little too much. The 5dB grid makes it easier to compare directly to posted charts from other people. 



> Based on the impulse response, I take 2.5ms as gating window: is that correct? This is my main question, really not sure if it's right... I follow (I think...) the instruction in the MiniDSP site but would be sure I got it.
> In my understanding, that window allow me to have a "pure" measurement until ~400 Hz, so can have the real behaviour of my speaker: am I correct? The response looks like a little bit flat to me, but again not sure if I'm right


That's correct.



> Can I use REW to understand the group delay? the configuration is MTMWW and I understand that I need to run the 2 mids as one driver for calculate the delay. In case I can't do with REW, can I import the results directly in Win PCD or do I need to extract the minimum phase?


I don't use passive XO modelers so am unsure of all the requirements and options. If you need find the delay relative driver offset with the UMIK-1 that could be done in HolmImpulse or Arta. Reportedly REW will soon have that capability, but it is not available yet.


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## jtalden (Mar 12, 2009)

stonemarten said:


> These are the measurements of the woofers outside, on axis. I can't find the impulse feedback, and I used a 10ms gating window. Is that right? Can I expand it? What do you think about the response?
> Both are at 1.5 mt. I have the 2 mt as well


It's tough to get an accurate SPL measurement of a woofer even outdoors. Proper setup is required. It looks like there were significant reflections in your measurement. It may be usable as I am not sure of the needs of the model. 10ms is only good to 100Hz. That may not be low enough for the XO model to work properly?

I would expect a cleaner response using a 'ground plane measurement technique'. Others will have more experience with passive XO modeling.

[If you had a MiniDSP or similar, then optional XO settings can be easily applied and measured. It is then easy to change the XO frequency, filter slopes, delays and levels needed to idealize each XO to a target response. Once the final XO frequency, filter slopes and driver offsets are found and evaluated, the passive XO can be fabricated. It's just another option. It's possible to get excellent result with just the passive XO modelers also.]


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## stonemarten (Jan 4, 2016)

jtalden,

thanks very much for your feedback, really appreciated!!



jtalden said:


> It's tough to get an accurate SPL measurement of a woofer even outdoors. Proper setup is required. It looks like there were significant reflections in your measurement. It may be usable as I am not sure of the needs of the model. 10ms is only good to 100Hz. That may not be low enough for the XO model to work properly?
> 
> I would expect a cleaner response using a 'ground plane measurement technique'. Others will have more experience with passive XO modeling.


I will and will post the results later. I've found this site mh-audio for Groundplane (can't post the link yet... less than 5 posts), and will follow the instructions there.



jtalden said:


> [If you had a MiniDSP or similar, then optional XO settings can be easily applied and measured. It is then easy to change the XO frequency, filter slopes, delays and levels needed to idealize each XO to a target response. Once the final XO frequency, filter slopes and driver offsets are found and evaluated, the passive XO can be fabricated. It's just another option. It's possible to get excellent result with just the passive XO modelers also.]


I do have  the 4x8. Basically I will run the MTM passive as one group and the WW as another as "2" drivers with active XO. I would like first understand if I design the box properly, then go forward and model the XO

cheers


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## 3ll3d00d (Jun 6, 2006)

stonemarten said:


> These are the measurements of the woofers outside, on axis. I can't find the impulse feedback, and I used a 10ms gating window. Is that right? Can I expand it? What do you think about the response?


I don't think they look healthy, there's clearly reflections in there as you can see from the series of peaks and nulls in the FR. Why are you measuring from so far away though?

if you're using WinPCD and a UMIK then I guess you plan to use minimum phase responses for modelling purposes and computed driver offsets including z offset? I don't think you have any choice really as the lack of a dual channel measurement means you can't get good relative phase data. 

The usual approach in that case is to calculate acoustic offset (there are instructions in the relevant tab in winpcd) and then measure each driver individually, splice near field and far field for the woofer and extract minimum phase using something like http://audio.claub.net/software/FRD_Blender/Blender.html

I use this approach myself with REW to take the data and I also wrote a script for generated polar sonagrams (https://github.com/3ll3d00d/directivity-utils) in case you want that sort of view.


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## natehansen66 (Feb 20, 2011)

Nice to see you've done your research and have a basic handle on impulse gating.

The problem with that short of a gate (2-4ms) is that while the fr does extend down to 400hz or so, that also means that you have a freq resolution that's only about 300-400hz. This has the effect of heavily smoothing the data below 2khz to the point where the details are wiped out. It makes it appear to be 1/2 or 1/3 octave smoothed, which also causes the level from 300-1khz appear to be lower than it actually is, making xo design difficult. 

What's your outdoor measurement setup like?


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks for the link to the script



3ll3d00d said:


> Why are you measuring from so far away though?


No specific reason: I can't find the reflection point so I took an arbitrary point... what do you think is a right gating? Anyway I will take again the ground measurement as per the previous post




3ll3d00d said:


> if you're using WinPCD and a UMIK then I guess you plan to use minimum phase responses for modelling purposes and computed driver offsets including z offset?


yes



3ll3d00d said:


> I don't think you have any choice really as the lack of a dual channel measurement means you can't get good relative phase data.


I do have all the dual channel measurements done with the mic in the same position (T+MM, T+W1, T+W2) as recommended for put in Win PCD for calculate the Z offset. Still I don't know what gating I need. In the example, it's 10ms: based on my files do you think is right?



3ll3d00d said:


> The usual approach in that case is to calculate acoustic offset (there are instructions in the relevant tab in winpcd) and then measure each driver individually, splice near field and far field for the woofer and extract minimum phase using something like


Do I still need to do all of this with the dual channel measurements, or can I use directly the results (with proper gating of course)? The example done with ARTA use directly the results: can I do the same?



natehansen66 said:


> The problem with that short of a gate...


thanks natehansen66: I had the same doubt because the response is too linear... how can I do better? smoothing? different gating?



natehansen66 said:


> What's your outdoor measurement setup like?


Only one wall at 3mt on the left, then wide open (15mt+) on every other direction, speaker on a cart at 15cm from the ground. I have some background noise (cars and trains) but I can run the test in the between, that is a kind of silent. The main issue are the house close to mine, that could complain...
Another one is that I can't take off axis because I can't put the mic in the middle of the road. Do you recommend to take all the measurements outside? Do I need the dual channel as well? Is 75dB still a good level?

thanks

cheers


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## 3ll3d00d (Jun 6, 2006)

stonemarten said:


> No specific reason: I can't find the reflection point so I took an arbitrary point... what do you think is a right gating? Anyway I will take again the ground measurement as per the previous post


honestly I don't know. Both your indoor and outdoor measurements (for woofer1) show a substantial spike in the IR at ~2-2.5ms which seems quite odd & the 1st ms or so is really going wild. I suspect you need to isolate the source of that first as that seems pretty messy. What sort of speaker are you measuring? how is it mounted? 

If I look at some of my data then I can see my woofer looks like it has a nice sharp/clean IR whereas a coax I have is a bit messy but still not as messy as the one you're showing.



stonemarten said:


> I do have all the dual channel measurements done with the mic in the same position (T+MM, T+W1, T+W2) as recommended for put in Win PCD for calculate the Z offset.


I'm confused. How are you taking a dual channel measurement with a UMIK-1?


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## stonemarten (Jan 4, 2016)

3ll3d00d,



3ll3d00d said:


> honestly I don't know. Both your indoor and outdoor measurements (for woofer1) show a substantial spike in the IR at ~2-2.5ms which seems quite odd & the 1st ms or so is really going wild. I suspect you need to isolate the source of that first as that seems pretty messy. What sort of speaker are you measuring? how is it mounted?


Could it be some ringing and/or standing wave inside the box, or just an external factor? 
I'm measuring a floorstanding speaker with flush mounted drivers

What about how to use the Mids and Tweeter response (gating, smoothing, etc.)? Any recommendation?




3ll3d00d said:


> I'm confused. How are you taking a dual channel measurement with a UMIK-1?


Not sure I answer properly to your question  I mean the measurements for calculate the Z offset as recommended by Jeff Bagby here http://techtalk.parts-express.com/showthread.php?229293-How-to-use-OmniMic-and-PCD-to-find-the-Relative-Acoustic-Offset. Is this what you were talking about?

thanks!

cheers


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## 3ll3d00d (Jun 6, 2006)

*Re: 3 way speaker measurements inside, outside &amp; group delay: am I right?*



stonemarten said:


> Could it be some ringing and/or standing wave inside the box, or just an external factor?
> I'm measuring a floorstanding speaker with flush mounted drivers


sound travels ~34cm in every 1ms so that gives you an idea of how far away the source of the "noise" could be, it's hard to say what it could be without knowing exactly what you're measuring and even then it might be tricky to debug remotely.



stonemarten said:


> What about how to use the Mids and Tweeter response (gating, smoothing, etc.)? Any recommendation?


your window looks reasonable to me though there is some indication that the same early noise is present in those measurements too, the magnitude is lower but that could be because the tweeter/mid is louder and naturally "faster" hence the initial peak is relatively larger.



stonemarten said:


> Not sure I answer properly to your question  I mean the measurements for calculate the Z offset as recommended by Jeff Bagby here http://techtalk.parts-express.com/s...-and-PCD-to-find-the-Relative-Acoustic-Offset. Is this what you were talking about?


OK I'm with you now, you mean paralleling multiple drivers in 1 measurement for calculating z offset. This is not a dual channel measurement, dual channel refers to measuring a 2nd input signal at the same time so that one can effectively subtract the electrical signal from the measured signal so that you get a cleaner view of the device under test.


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks for your input: around that distance there is the most far wall inside the cabinet and the cart I'm using to move the speaker: these are the only 2 constant things in the indoor and outdoor measurements.

let me investigate what's the cause and will be back here for further comments

cheers


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## 3ll3d00d (Jun 6, 2006)

stonemarten said:


> thanks for your input: around that distance there is the most far wall inside the cabinet and the cart I'm using to move the speaker: these are the only 2 constant things in the indoor and outdoor measurements.


A pic of your speaker and measurement setup might be useful here


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## stonemarten (Jan 4, 2016)

3ll3d00d,

I investigated what could be that ~1ms reflection: the cart handle (a steel pipe around 25mm diameter) is exactly at 35 cm from the speaker axis... don't know if it is the cause, but I will measure again without the cart and see if I have still the problem

speaker









( the second woofer it's at the very bottom, close to the floor, you can see in the model below)

measurement set up

















Room size (in mt): 5.5 x 2.7 x h 2.2
Speaker at 10cm from the floor, tweeter axis at 1.1mt, mic at 1.5mt on axis, 15 and 60 deg

please let me know if you need more details

thanks!

cheers


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## 3ll3d00d (Jun 6, 2006)

that handle sounds like a good candidate for an early reflection 

getting a good measurement from the woofer will be tricky with it on the floor like & the dimensions of the room might make it difficult to do anything else. I wonder whether you might be better off rotating your whole setup by 90 degrees so you have it mounted horizontally rather than floor to ceiling? you might lose a bit of resolution from the tweeter but gain a fair bit on the woofer.


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## stonemarten (Jan 4, 2016)

I would first focus on get the MTM part right, and get the right measurement. 

I will try later to get that group work together with the 2 woofers: at the same time, I will do a ground measurement for see the individual woofers response

thanks!

cheers


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks for spot the problem: looks like nothing strange until around 2.5ms, at least I think . 
What you and the other experts think? Can you please let me know? thanks!

tweeter on axis















15 deg















mids on axis















15 deg















cheers


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## stonemarten (Jan 4, 2016)

Dear experts,

I take the woofer ground measurements (75dB, mic at 2mt, driver axis pointed to the mic tilting the box): below the results.

Can you please let me know your feedback:
- does the response make sense?
- do you see any ringing/standing waves? 
- is normal that the response doesn't have any flat part, but just goes down?

Any other comments welcome!!

woofer 1















woofer 2















thanks!

cheers


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## 3ll3d00d (Jun 6, 2006)

You have posted the envelope rather than the impulse and the frequency range is unusually wide, probably best to repost the graphs.

I still think you have a strong early reflection BTW, especially in the mids, which, I think, is causing that ripple in the FR. It seems unusual to me. 

Where is the left window set BTW?


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## stonemarten (Jan 4, 2016)

3ll3d00d,

sorry for the graph, still learning 

I hope these graphs are correct now: please let me know if you want the mdat files

I didn't touch the left window setting from the deafult: do I need to gate that side as well?

woofer 1















woofer 2















thanks!!!

cheers


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## Phillips (Aug 12, 2011)

Link below might help

http://www.hometheatershack.com/forums/rew-forum/67786-settings-rew-nearfield-measurements.html


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## stonemarten (Jan 4, 2016)

Phillips,

thanks for the link, appreciated. Based on that post, these are the differences in my set up

- I'm using a camera tripod: could this be one of the issue? if yes, I will buy a mic stand. Anyway I don't use anything for ground measurement
- I use the default Turkey 0.25: do I need to use the Blackman-Harris 7? I've tried and I got a frequency resolution of 35 Hz: is that fine?
- No left window gating: I don't know how to define it. Do I need to be symmetric? Double?

Can you please help me with my questions?

thanks!

cheers


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## 3ll3d00d (Jun 6, 2006)

stonemarten said:


> - I'm using a camera tripod: could this be one of the issue? if yes, I will buy a mic stand. Anyway I don't use anything for ground measurement
> - I use the default Turkey 0.25: do I need to use the Blackman-Harris 7? I've tried and I got a frequency resolution of 35 Hz: is that fine?
> - No left window gating: I don't know how to define it. Do I need to be symmetric? Double?


I would start by bringing the left window in so it is just including the start of the impulse, something like 0.3-0.5ms perhaps. This will reduce the frequency resolution accordingly and remove the low end. The default window is tuned for room analysis.

BH7 tapers for longer so gives wider window with more emphasis on the early part. This might be useful if you had a weak reflection a few ms in and then nothing for a while longer (for example). Arguably there is as much art as science in how you analyse this data  

Posting the mdat might help here.

A mic stand is useful for sure, some people take great care to extend it further to even eliminate that as a source of reflections.


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks for your feedback as always!!!

I will buy a mic stand later 

thanks to the admin I've uploaded the woofer open measurements
Woofer 1 
View attachment wf1 open.mdat

Woofer 2
View attachment wf2 open.mdat


And also the rest...
Mids
View attachment Mids 1.mdat

Tweeter
View attachment tweeter 1.mdat


All in one file
View attachment Combined.mdat



Tweeter and mids sorted out 
cheers


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## stonemarten (Jan 4, 2016)

All mdats file uploaded!! Looking forward to your comments!!

cheers


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## 3ll3d00d (Jun 6, 2006)

something like this window looks appropriate for the data to me









the FR does still have that ripple in it though which seems a little odd to me, I would think it comes from that early bump in the FR in the mid/tweeter
















if you can isolate and remove that effect then I imagine the data quality will improve. I guess the question is whether it's a function of the driver itself, the way it's mounted or the measurement setup. 

The woofer looks quite curious, it is like it rings after the initial impulse with a period of ~250us (i.e. ~4kHz). The FR also shows a peak at 3.65kHz so perhaps that ringing is the woofer breakup? It might be interesting to run that sweep full range to see if it changes. AFAIK the REW sweep actually continues for another octave (so to 8kHz) which I think is to avoid measurement artefacts at the end of the sweep bandwidth but would be worth repeating full range to double check.


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks for your comments! I redid the measurements with a mic stand, and I think they look better than before already. Here the tweeter









do you still see something wrong? looks like that strange behaviour is gone to me...









mids impulse with the limit at 6k Hz









what do you think? here too looks like the strange things are gone...

mids response with the full sweep

















looking forward to your comments again!

I can't measure the woofers because outside is snowing... when dry out I will again
Please let me know if you need the mdat

thanks 

cheers


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## 3ll3d00d (Jun 6, 2006)

I agree it looks much better now


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## stonemarten (Jan 4, 2016)

Finally outside it's dry and I can measure the woofers :sn:

As per your recommendation, I run the full sweep (20~20k), using ground measurement 

Woofer 1 impulse









Zoomed









Response









Woofer 2 impulse









Zoomed









Response









For testing, I've run a sweep from 60 to 1000 (driver resonance is 60 Hz)

wf1 

















wf2

















I still see a long wave, and I'm not sure now it's right or not...

What do you think? Do you see if there are any ringing or signal the box is not appropriate/stiff enough?

Every comment is welcome!! 

thanks

cheers


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## 3ll3d00d (Jun 6, 2006)

I wouldn't use a hann window with that measurement, it looks cleaner for a lot longer so the taper in the hann window will suppress the LF output unnecessarily. Try a tukey 0.25 that lands at the same spot (~11ms) and post back.


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks very much for your suggestion!!! Here the updated FR

wf1 

















wf2

















same gating with the 60-1k sweep

wf1









wf2









looking forward to your comments 

thanks

cheers


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## 3ll3d00d (Jun 6, 2006)

not as big a difference as I thought might be seen but you can still see how the knee sharpens below 200Hz once you remove the taper from the window

it seems to rolloff quite high for a woofer though, does this look like you're expecting from a model (of the box response + baffle effects)?


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## stonemarten (Jan 4, 2016)

3ll3d00d,

sorry for the delay but the forum was under maintenance yesterday

Below the response overlapped with the Frequency Response Modeler from Jeff Bagby (in yellow)

woofer 1









woofer 2









They are pretty close, so yes, this is what I expected.
Do you see any strange things, like ringing or standing wave from the box?

thanks!

cheers


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## 3ll3d00d (Jun 6, 2006)

I guess the Q is where that discrepancy in the 800Hz region comes from? I suppose you're seeing a baffle step induced peak there but your model doesn't show it, suggests the model is wrong?


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## stonemarten (Jan 4, 2016)

3ll3d00d,

thanks for the comment: I've tried to play a little bit with the simulator and even if I change the box related parameters (size, loss, etc.) the result remain more or less the same...

then yes, if I assume the measurements are correct the model is wrong

thanks again for the help: will post later after I add the crossover 

cheers


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