Hi
@detlev24 thanks for taking the time to review my talk. Many years ago, I was a partner in an acoustics manufacturing company where we designed and developed bass traps, broadband absorbers and diffuser panels. We had our products tested in an anechoic chamber and used them in many critical listening rooms, studio control rooms, movie theatres, etc. Attached is small review from Andrew Marshall's Ideas Guide from a long (long!) time ago.
Here is the issue and taking a line from Ethan's site from the links you referenced, "It's true their absorption is less than above 80-100 Hz, but you make up for that by having more of them." What is not being said is that by "having more of them" means "stuffing" the room with bass traps. But while stuffing the room with bass traps can be effective below 100 Hz means that above 100 Hz there is way too much absorption and typically produces a huge hole in the frequency response in the 200 to 300 Hz region where the bass traps are at maximum efficiency. I see it/measure it over and over again where folks have stuffed their room with bass traps and we need to yank them out. Mostly in studio control rooms, but also in home listening rooms.
This is what I meant by absorb by equal amplitude. In order to get the performance below 100 Hz, by stuffing the room, you are also going to absorb above 100 Hz. Bass traps are "not surgical" by affecting the one range of frequencies of interest, but not another range. For sure one can somewhat even out the peaks and dips with trapping, but it takes a lot of them (i.e. gets expensive fast in addition to the decor if it is a home listening room). And as mentioned, usually at the expense of having way too much absorption above the room's transition frequency, unless one has purchased "Helmholtz resonators" which are even more expensive than typical bass traps.
As I have stated many times before, I am not against acoustic treatment and I use some in my own listening room, and spec for other rooms, but it is typically used to bring down the overall broadband decay time to meet
industry standard specifications. For home listening environments, my experience is that unless one's room is complete devoid of any absorption, most rooms broadband decay time falls within the industry specs, without any room treatment. I say that having measured hundreds of rooms over decades.
The most efficient and cost effective way with dealing with the
inevitable uneven bass response in a room is via DSP/DRC. I mean state of the art DSP where not only the frequency response is even, but also the low frequency reflections over time have been taken care of (i.e. the ideal minimum phase response has been restored). Here is an example of what I mean. Stand a mic up at the listening position and using REW, with its default 500ms window which lets a good portion of the room reflections through. Note this chart has no smoothing applied:
Below 200 Hz we see both frequency and phase are "textbook" perfect (and not at just one listening position as my book goes into detail verifying at many locations) and above we are starting to let the room reflections through, on purpose. I would hazard a guess that most folks have not heard even bass response in their rooms before, so using some level of DSP/DRC to smooth the low frequency response is a big step up. However, also correcting for excess phase in the low frequencies increases the clarity of the bass response where few folks have ever heard before. Every bass note is not only even, but crystal clear. Before DSP, I have only heard that quality of bass response in proper acoustically designed control rooms that go way beyond just acoustic treatments, but that is a whole different post
I hope you are enjoying the music!
