Sound Absorption of Walls

RevMen

The Reverend Menacer
I just stumbled across this looking for something else. The Green Glue company performed an unusual combination TL and absorption test on a series of wall construction mock-ups. They couldn't assign absorption coefficients to the panels, as they were unable to test an "empty" room, but they were able to make comparisons between wall types based on measured reverb time.

They concluded that staggered or double stud walls are the best absorbers. The also provide the best transmission loss, so this is even more reason to consider using this type of construction if you're about to construct a dedicated listening room or home theater.

http://www.greengluecompany.com/soundAbsorption.php

In a series of lab sessions in 2005, The Green Glue Company set out on perhaps the most ambitious project ever aimed at studying the sound absorbing properties of walls. The project spanned dozens of walls, of many different configurations, with a series of experiments designed to explore the questions listed above.
In the pages below we will present the fruits of this work. While the series of experiments were not perfect, a great deal was learned, and answers to all but one of the questions listed above seem to be attained.

CONCLUSION
We have taken a look at data that hopes to address some common questions about the absorption behavior of walls.
The most important conclusion is that absorption in walls is directly tied to the resonant behavior of the walls.
Beyond that, it appears that viscoelastic damping may have some benefits with respect to wall absorption, and that resilient decoupling methods such as resilient channel change the low frequency absorption of walls, but don’t necessarily improve it. They are better at some frequencies, and worse at others.
It is demonstrated that adding mass in and of itself does not result in reduced absorption in a simple panel or the common single wood stud wall, but does have a much more pronounced effect on resiliently decoupled walls.
It is demonstrated that transmission loss and absorption are not correlated.
Finally, it appears based on this work that the best starting points for sound absorption at low frequencies are staggered or double wood stud walls. These walls exhibit resonant behavior over a broader range than other wall types, and as a result appear to offer a broader range of effective absorption.
In the near future, The Green Glue Company will publish addition tests, and also a large database to help designers predict the location of resonances in various types of walls. This should prove helpful, since absorption and resonance are so closely related. Make sure to browse the appendices, where we take a look at the mass-vs-absorption debate, and try to estimate the absorption coefficient of some of these walls based on what data we have.
 
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