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Scott Dorsey Scott Dorsey is offline
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Default Adding Multiple Absorption Coefficients

Sean B wrote:

So let's say I have two different acoustic absorbers covering most of the a=
rea of a room, say a bass absorber and a higher broadband absorber. They cr=
oss over at around 250 Hz. If both have a 0.5 absorption coefficient at 25=
0 Hz, how do I calculate a total absorption figure for both acting at the s=
ame time?


A square foot of a thing with a 0.5 absorption coefficient has the same
effectiveness as half a square feet of open window (which has an effectiveness
of 1.0). If you have a thing with a 0.25 absorption coefficient, you will
need four square feet of it to get the same effectiveness as a square foot
of open window.

Multiply the absorption coefficient of all the materials in the room by the
area of each of those materials, sum them up and get the total room absorption.
In a larger room you can plug this into the sabine equation and get the
reverb time of the room. In a smaller room where you don't care about the
total reverb time so much as specific room resonances, it's a little harder
but the relevant equations are in the F. Alton Everest book on small studio
acoustics.
--scott

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"C'est un Nagra. C'est suisse, et tres, tres precis."