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Natural Science Forum / Physics / Acoustics / February 2004Acoustic room profiling help requested - measurements and data interpretation
I'd like to get your suggestions on a good way to look at acoustic room response for purposed of equalization. I'm thinking that I can play some wideband tones, which get recorded into a PC via a microphone. Does anyone have any suggestions on the tones that would be good to use? Once the data is recorded in my PC, what type of processing needs to take place to 'characterize' the room? (taking the inverse FT, etc.?) If someone has a idea on a procedure for this I'd like to hear what you have to say. Thx. Hi Larry, Could you give a little more detail please? I am not sure what you want to achieve - altering room acoustics with equalisation is not entirely practical. There are applications available that will largely do what you want - I think acoustic mirror may be one. Andrew > I'd like to get your suggestions on a good way to look at acoustic room > response for purposed of equalization. [quoted text clipped - 9 lines] > > Thx. Larry, > I'd like to get your suggestions on a good way to look at acoustic room response for purposed of equalization. < Forget it. You can't solve room acoustic problems using EQ. And the newer, more sophisticated DSP devices that *claim* to solve room problems are also a waste of time. The reasons this doesn't work are long and many, but briefly: * The inevitable peaks and severe nulls that exist in all untreated rooms vary around the room. So if you EQ to make the response good in one place you'll make it worse in others. You can't even EQ a single "sweet spot" to be correct because there are large changes in response across a span of just one or two inches. * Another big problem in most rooms is lack of clarity due to excess reverb time at low frequencies. Of course, EQ can't do anything for that either. The correct solution for room acoustic problems is broadband acoustic treatment that is effective to the lowest frequencies. --Ethan > Forget it. You can't solve room acoustic problems using EQ. And the newer, > more sophisticated DSP devices that *claim* to solve room problems are also > a waste of time. The reasons this doesn't work are long and many, AMEN! > * The inevitable peaks and severe nulls that exist in all untreated rooms > vary around the room. So if you EQ to make the response good in one place > you'll make it worse in others. You can't even EQ a single "sweet spot" to > be correct because there are large changes in response across a span of just > one or two inches. If you study photographs of the interior of the old music hall favorites (Musikverein, etc.), you will see that, though the rooms often are largely rectangular, on the scale of the wavelength of important frequencies (100-4000Hz, or 1/3' to 10'), the room surfaces are highly irregular (niches, objects, bric-a-brac, etc.). This is NO accident! The physics behind this fact is that DIFFUSION is the only tool we have to "EQ" the room itself. That is, these diffusions tend to flatten out the room response over the important sonic frequencies. Below 100 Hz, the surface shape perturbations required are too large to be ignored by the architect (and zoning authorities), so instead, those music halls that remain popular are coincidentally fitted with de facto bass traps in the form of wood panels (hence "wood is good"), HVAC openings, etc. My crass theory about "successful" old music halls is that they were not overtly designed to be outstandingly successful. Rather, many were built throughout the ages, but only those survived (not torn down due to insufficient use) that had the necessary attributes. (Can we stretch this logic to say that God designed them??!) Angelo Campanella --------- www.CampanellaAcoustics.com --------- "I have simply studied carefully whatever I've undertaken, and tried to hold a reserve that would carry me through." - Charles A. Lindbergh. "As for background noise level; 35 dBA is a good classroom; 45 dBA is a sound masking system!" - Anthony K. Hoover Angelo, > If you study photographs of the interior of the old music hall favorites < My expertise, such as it is, relates only to small rooms and their treatment. I assumed that Larry, the original poster, was asking about using EQ in a small room to make it suitable for mixing because I see people ask that almost daily in other groups. Small rooms present a completely different set of problems than concert halls, especially at the low end, because the modes are so much farther apart, and because acoustic interference is much stronger off the nearby walls and ceiling. > (Can we stretch this logic to say that God designed them??!) < Nah, let's stick to science and what can be proven empirically. :->) --Ethan take a look at www.audiophileconcept.com > I'd like to get your suggestions on a good way to look at acoustic room > response for purposed of equalization. [quoted text clipped - 9 lines] > > Thx. |
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