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Moving Mic Measurement
Moving Mic Measurement
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Old 20th September 2014, 01:23 PM   #1
jlo is offline jlo  France
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Default MMM Moving Mic Measurement

Hi all,

to measure loudspeakers in a room, here is a presentation of my MMM method.
It is not a revolutionary method but it is quick and reliable.
http://www.ohl.to/audio/downloads/MM...easurement.pdf
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Last edited by jlo; 20th September 2014 at 03:50 PM.
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Old 21st September 2014, 06:54 AM   #2
Juhazi is offline Juhazi  Finland
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Thank you jlo! I read and downloaded your pdf. 1-2kHz region is very sensitive to small movements of speaker or microphone (reflections!)

Room measurements should never be done at only one mic location. My friends have learned to me an easy way to do multiple measurement.

We use REW in RTA mode, Forever averaging. Play pink noise or pulsating pink noise with one or more speakers at the time, start RTA recording and move the mic slowly, 3-dimensionally around your head at your "sweet spot". The radius of movement should be 0.5m (2 feet). Continue recording for say 15 seconds. Then after stopping you can toggle for varius smoothing to see how the response looks.

The measurement reflects true room power response and audible spectral balance well. For learning measure several different speakers and compare measurements to your audition (how you hear them to sound).
Attached Images
File Type: jpg rotating mic rta.jpg (126.4 KB, 1274 views)
File Type: jpg ainogneob v74 l r spl rta-vert.jpg (178.4 KB, 1256 views)
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Last edited by Juhazi; 21st September 2014 at 07:01 AM.
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Old 21st September 2014, 01:14 PM   #3
Legis is offline Legis  Finland
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I should try that too. Shouldn't pink noise have decreasing slope and white noise has "straight line"?
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Old 21st September 2014, 02:41 PM   #4
Juhazi is offline Juhazi  Finland
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Yes by definition, but pink will measure flat! ½ or 1/3 oct smoothing is best. If L and R are playing simultaneously, highest treble will descend a little because of interferences.
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Old 21st September 2014, 03:07 PM   #5
Pano is offline Pano  United States
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Moving Mic Measurement
Merci Jean-Luc! This is new to me. Certainly the averaged muti-position technique is well known, but the moving mic method is an interesting progression of that. Will have to give it a try.
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Old 21st September 2014, 03:31 PM   #6
Pano is offline Pano  United States
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Moving Mic Measurement
Juhazi - in ARTA using periodic pink noise, the measurement could be set to do 175 or even 200 averages. 60 secs is about 175, which should give good resolution down low.
I won't be able to test this until Tuesday, but will do so then and report my results.
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Old 22nd September 2014, 10:12 AM   #7
Legis is offline Legis  Finland
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Quote:
Originally Posted by Juhazi View Post
Yes by definition, but pink will measure flat! ½ or 1/3 oct smoothing is best. If L and R are playing simultaneously, highest treble will descend a little because of interferences.

Here's 1ch, non-smoothed sweep vs. pink from listening sofa's back rest (non-moving mic). Pink noise (black curve) has noticeably more descending curve. White noise behaves like the sweep.

Click the image to open in full size.

Last edited by Legis; 22nd September 2014 at 10:15 AM.
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Old 22nd September 2014, 10:41 AM   #8
Legis is offline Legis  Finland
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1/48oct smoothed sweep vs. moving mic white noise measured from listening spot:

Click the image to open in full size.
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Old 22nd September 2014, 12:19 PM   #9
Juhazi is offline Juhazi  Finland
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Strange! Here are my fresh measeurements - pink noise gives similar response to sine sweep! REW v5.1 beta22, digital out to ObjectiveDAC, measured with calibrated UMIK-1.

I wonder what is causing this difference to Legis' measurements?

Edit -I found it! Legis didn't have RTA mode set at RTA properties in REW
Attached Images
File Type: png ainogneob l spl vs rta pink.png (72.0 KB, 1148 views)
File Type: png ainogneob l spl vs rta white.png (72.1 KB, 192 views)
File Type: jpg rta mode set rew.jpg (109.7 KB, 235 views)
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Last edited by Juhazi; 22nd September 2014 at 12:44 PM.
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Old 22nd September 2014, 12:34 PM   #10
Legis is offline Legis  Finland
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Juhazi, try "Spectrum" view instead of 1/48oct RTA. I Just noticed this, but I don't know why they have such a difference?? Very strange, maybe a bug? Also the level in spectrum view drops drastically. I wondered why I had to play so loud...

Last edited by Legis; 22nd September 2014 at 12:37 PM.
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