Originally Posted by dknightd
OP here is one recent related thread
There are many others here. Some more useful than others.
I think you'll find that there really is no real agreement on how to best to treat a room. And I think that is because no room/speaker arrangement is the same.
The theory is pretty easy if you treat a whole wall (floor or ceiling), and assume all sound approaches that boundary perpendicularly. But that does not happen
in most real spaces.
Air gaps can be useful, but they essentially make a tuned cavity - better absorption at some frequencies, less at others. That may or may not be a good solution.
If upstate NY is near Albany drop me a PM. It might be fun to get together and talk/listen.
The most significant problem is that there is less agreement in the specific acoustic response one wants to achieve!
Once well defined, achieving a desired specified response is not that difficult!
I am not sure to what theory you refer regarding treating the "whole wall". Nor is it clear that any theory becomes "easier" as a result.
The behavior of absorption, reflection and diffusion is well understood and predictable at all angles of incidence, so I am not sure where the notion that normal incidence is anything special - except to say that the degree will vary from that oft cited reference. That is simply a factor that one observes in the process of being aware of the full range of behavior in real rooms, and a reason that measurements in situ are so valuable, especially for those for whole calculations are a challenge.
Ar gaps with porous absorption are seldom tuned cavities unless specifically designed, and thus far no one has proposed tuned resonant treatments which do utilize tuned cavities. A gapped absorber is NOT a tuned trap. It simply takes advantage of the optimal 1/4 wavelength spacing whereby the particle velocity is maximum at the 1/4 or 3/4 wavelength points, eschewing the placement of porous material in the region of the boundary 0/4 or 1/2 wavelength points where velocity goes to zero and the material losses efficiency and the placement of material reaches a point of diminishing returns.
All in all, I am not sure what the big issue is here.
The behavior of porous materials is rather well understood, and with the advent of a few additional predictive modelling tools based on a plethora of very accurate mathematical material models, our understanding of the various materials now extends outside of the simple cursory measurements of a few commercially available products. And those tools have led to the modification of a few older, but oft cited treatment models.
Two such examples of heretofore commonly accepted 'rules' that have been modified, but which are routinely debated and of which many are still unaware, are in the constitution of the 'Superchunk' style corner traps and in the advantage of unframed absorptive panels over framed. The first being modified to account for the superior low frequency behavior of lower gas flow resistance(GFR) fill and the later due to the recent investigations in to the effects of edge diffraction, whose loss contribution is roughly equal to that of the small amount of additional porous surface area, rendering the choice pretty much as a 'wash'.
But the fact remains that while porous materials are relatively cheap and easily worked, that they are not optimal for the control of low frequencies if efficient space utilization is a prime concern. For that purpose you turn to tuned resonant traps - another area that has been well understood for a long time as well - although the calculations and the subsequent in situ adjustments may not be to the liking of someone not familiar with the math. measurement and iterative adjustments necessary for optimal implementation.
But as local has suggested, such information for the most part is presented in Acoustic Absorbers and Diffusors
, or in the associated reference materials if one wants to read the details of each specific mechanical behavioral model.
So if one wants to assert that they are not intimate with all of the acoustical models, or that they they are not intimate or comfortable with such mechanical material information and the associated design processes, that's fine.
But it seems to me that a much larger issue that continues to exist is that most are not aware of the various acoustical response models in order to decide exactly what response they desire, and then they continue to look for a one size fits all treatment that is supposed to magically 'correct' any space regardless of topology simply by following a cookie cutter design placed in a standard one size fits all location in a room whose topology and the equipment and listening position within vary individually!
The fact is, while there are a few standardized treatment designs that will accommodate quite a few applications, for all the rest a few preliminary decisions must be made first regarding the desired acoustical response, and then a few simple measurements will need to be made in order to refine those 'generalized' specifications into actionable and optimal room specific treatments and their positioning to achieve the desired response.
The failure of most to do the necessary per-requisite work does not lead one to the proper conclusion that the 'what' to do and 'how' to achieve the response is neither agreed upon nor understood.
Nor does the fact that many are want to use porous materials and yet are unwilling to accept the design parameters that go along with both the material and spacing limitations of a velocity based treatment.