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adamparin
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Joined: Apr 21 2008 - 12:27pm
How Do I Actually Measure the Acoustic Modes of My Listening Room?

I am lucky enough to work as an engineer for a noise and vibration control company, mostly for aerospace issues. I work mainly in the vibration damping sector, but I have brought home with me a pretty cool little device to measure the acoustics of my listening room. Its a nifty little four channel front end analyzer from Squadriga and a Binaural Headset for Sound Pressure Readings. I can take all the different octave bands, but I assume narrow band is what I want to take my measurements in.

My plan is to do the following:
1. Determine a test album where I play the same 15 seconds of music for each recording - if anyone has a good suggestion, I am all ears.
2. Take my first recording at my primary listening position for 15 seconds.
3. Then move around (in a grid like pattern) taking the same reading with my the sound level transducers from the headset at the same height as my seated position. I will probably make a grid of 6 columns and rows. - Will this be sufficient for mapping out the acoustic modes?
4. After all of the data has been taken, I am planning on analyzing it in a post processor looking at the narrow band frequency data. I will first try to pick out the 1,1 mode of the listening room in both the length and width by looking at frequencies that have large amplitudes in the middle of the room and smaller as they move to the edge along the center axis. Then proceed through the modes trying to determine what frequency has the most issues at my primary listening position and which mode this is associated with so that I can then use a sound absorbing panel where the unwanted frequency is hitting the wall.

So tell me how much has my vibration background screwed up my understanding of what to test? I am basically trying to run a vibration modal analysis but with sound pressure readings, is that going to accomplish anything worthwhile?

Thanks for any help.

Kal Rubinson
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Re: How Do I Actually Measure the Acoustic Modes of My Listening

I suggest that there are easier ways to do this but I must admit that I am not familiar with the tools you intend to use. The descriptions of their applications are vague to me and do not seem directly relevant to the problems of room modes and room acoustics. I suggest that you look at Everest's Master Handbook of Acoustics and consider playing with Room EQ Wizard (freeware) to see the general and usual approaches to this. It would be interesting to see how one can apply this binaural device to them.

Kal

adamparin
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Re: How Do I Actually Measure the Acoustic Modes of My Listening

I've already looked at the theoretical mode stuff, however, my listening room is my living room and its slightly different that a normal box. It was a huge cutout on one wall that goes into the kitchen 4 feet higher than the living room. I assume that to determine all of this room acoustics a simple sound pressure readings would be suffice, but since my knowledge is in suppressing noise from structure born resonances, this is slightly out of my knowledge base.

Oh and their application is - the headset is two sound pressure transducers, (a mic) one on each ear. The 4 channel analyzer is basically a small FFT analyzer that takes the Time Domain data from the mic and runs a Fast Fourier Transform to take it to the Frequency Domain. We typically use the device on flights and in automobiles to get actual noise data at the ear positions in different locations.

Kal Rubinson
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Re: How Do I Actually Measure the Acoustic Modes of My Listening

Yeah. I got that but it is still not clear to me that it offers any advantages unless it is accompanied by appropriate application software and that I do not see. For example, ETF/RplusD will not only do analysis but make suggestions for correction. http://www.etfacoustic.com/RPlusDSite/index.html

Kal

ethanwiner
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Re: How Do I Actually Measure the Acoustic Modes of My Listening


Quote:
Determine a test album where I play the same 15 seconds of music for each recording


Stop right there. Music is unsuitable for room testing because it contains only those frequencies related to that music's key. Kal's suggestion to read up on ETF/R+D is what I'd have said if he didn't beat me to it. You may find my write-up useful too:

Using ETF

--Ethan

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