[Savant]

Ethan: The actual number of sabins measured in a lab will not jive with the actual number of sabins measured in a small room. That was my point. A lab is an idealized situation. If a 72 ft² area of absorbers is placed in a lab and measures 78 sabins at 500 Hz, that's indicative of the performance in a large space, but not exactly. When modeling larger rooms, it is assumed that this is an exact number, but the predictive results clearly show that the same amount of absorption was not, in fact, added to the real-world room. The lab assumes (and delivers, over the standard frequency range) statistical reverberance. The big auditorium where the absorbers are being placed on the wall (in much greater quantities) is not usually quite so idealized.

Take this one step further and make the room very small like a studio room, and the entire concept of sabins goes out the window. Whether sabins/unit or absorption coefficients, the numbers are really only useful for the most cursory of comparisons. Beyond that, the performance is situation specific for both low and high frequencies.

The main reason this happens is because the result - sabins of absorption - is calculated using differences in decay. Since there is no linear relationship between the decay change that occurs in a chamber and the decay change that occurs in a studio room when the same amount of absorption is added to each, the results cannot be the same. There is a volumetric relationship in the purely theoretical sense. But there are other factors controlling the actual results that are largely being ignored when absorption is measured in a small room.

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ddageek: I guess we could all get together and do that. However, since - as I mentioned - such standards do exist, the only thing we'd accomplish is a reinvention of the wheel. (Assuming we could all work together!!! )

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Others: The argument about too much LF absorption being possible should be clarified a little bit for the contexts of this thread:

(a) If the goal is a "flat" frequency response, then too much LF absorption is probably not likely in most small rooms. But it would be possible.

(b) If the goal is a "flat" time response, then I would argue. Most rooms - even studio control rooms - should not be "flat" in terms of their time response. So, if the goal is an even time response with a slight rise in the low-end, then too much LF absorption is not only possible, but more probable than in the case of (a) above.

(c) It is possible that the reason many seasoned acousticians find over-absorption of the low-end common is because the absorbers being used are also absorbing the high frequencies. If this is the case, too much of a good thing ("traps") is possible and can indeed lead to too much of a bad thing (dull response on the high end).

(d) It is also possible that the seasoned acousticians are over-generalizing. This is less likely if the acousticians in question were being specifically queried on studios. However, it is common to find cases of over-absorption of the low-end in large rooms.

So, if I were asked, I would say that over-absorption of the low-end is possible. Whether or not it's probable would depend on what kind of situation we were discussing.

The same sort of generalization holds true, I find, for most things in audio and acoustics.