Thomas,
Good points, and all are worthy of further discussion. First let me say that there is no question that panel traps work, and work very well. This started when you said "Panel traps are very inefficient" which simply is not true. Aside from the ASTM measurements performed on the traps I sell, I have been building panel traps for many years. In every case they changed a room that was impossible to mix in, into a room that sounds great and is a joy to use. I have sold more than a hundred panel traps through my company, and every customer has been extremely pleased. Nobody has ever asked for their money back, and I have received many positive comments. Our last sale was to Jerry Barnes at Avatar Studios in New York City, and he was beside himself with praise for how much they improved his mix room.
I'm sorry if this sounds like an ad
but there is
no question that panel traps, when properly built, are extremely effective. How they work and how they might be measured is surely worthy of discussion.
> "Overcoming inertia" is just a another way of looking at impedance. <
Fair enough, but panel traps are linear in their operation. If you excite them at low volumes they respond with small movement. At higher levels the panels move more. You can no more point to "inertia" as a negative in a panel trap than you can in every cone-based loudspeaker ever made.
> I looked at your data, but like any good scientist, I have to approach it with a great deal of skepticism - especially when my understanding of the physical model seems in contradiction. <
I have no problem with skepticism. I subscribe to four different skeptic magazines, so I am very aware of the need for skepticism in every field, not just audio!
> is this reverberant room method appropriate for a system which could potentially be better characterized as resonant rather than absorptive? <
Sure it's appropriate. Why wouldn't it be? Further, how else would you measure the absorption of panel traps at various frequencies?
> For example, the phase of any reflected signal might influence the data depending on where the test microphone is positioned. <
That is way off. When an ASTM lab measures absorption, the microphone is constantly in motion. Further, hundreds of separate tests are performed and the results are all averaged. At IBM's lab which we use, each test takes about 40 minutes to complete because so many tests are performed and with so many mike positions.
> In the very deep bass where the wavelength is large compared to the room dimensions <
I agree that the sine wave data I show is not as useful as a legitimate test. The problem is that no lab in the world can test at those low frequencies, so a half-assed test using tones was all we could come up with for very low frequencies. Also, bear in mind that the room dimensions at very low frequencies are much larger than where the walls are physically. Very low frequencies go right through normal sheetrock walls, so the real walls are whatever lies beyond that is more massive. In this case the control room is inside a basement, and the cinder block walls are quite a distance away from the inner sheetrock walls.
> This could make sense if the bass traps had virtually no effectiveness in this frequency range and simply tightened up the room by adding mass to the walls. <
That could well be the case. I have no idea, nor do I even have a suggestion for a better way to test that. But it's a mistake to dismiss panel traps for not absorbing much below, say 45 Hz., when they work so very well at higher bass frequencies. And for most studios, the important frequencies are 80 Hz. and above. More to the point, how effective is any other type of broadband absorber below 45 Hz.?
--Ethan