Reverberation Chamber

A reverberation chamber reflects sound energy at every boundary and lets the field diffuse fully inside the room, so that the energy density is even everywhere and the sound spreads randomly in all directions. It is used mainly to measure the absorption coefficient of materials, to measure sound absorption in air, to characterize the sound power and spectrum of sources and machinery, to evaluate the efficiency of electroacoustic devices, and to run noise fatigue testing on precision components.

The common volume is 70 to 300 cubic meters, with a standard chamber sitting around 200 cubic meters plus or minus 10%. The lowest test frequency is 125Hz for one octave bands or 100Hz for one third octave bands, reverberation times run from a few seconds to tens of seconds, the average absorption coefficient stays no higher than 0.06, and the standard deviation of sound pressure across measurement points stays below 1dB.

To keep the field diffuse, the room uses an irregular set of proportions so that no two dimensions form a whole number ratio. The walls are finished with hard reflective surfaces such as enamel, tile or copper foil, and fixed diffuser panels and large rotating diffusers can be hung to improve the uniformity of the field still further.