As for absorbing linings for testing rooms such as anechoic or semi-anechoic rooms (including: aero-acoustic wind tunnels) are concerned, they generally consists of multilayer modules sometimes (quite often: made of mineral wool or of polyester wool or of melamine foam) often covered by a surfacing (most often: a fiber glass or a polyester cover) and (in many cases) and by a perforated protection (mostly: galvanized or painted steel). A powder coating usually provides the best protection against corrosion: classification up to C5 according to ISO 12944 while providing a visula aspect appropriate for the the context.
In some cases, the frame of the plane absorbing lining in a test room can be made of stainless steel (SS 304, SS 316) or aluminum.
As required, the absorbing lining may be, for some applications, protected by a waterproof surfacing (polyurethane film and for extreme cases: painting).
In order to increase the absorption coefficient in a given frequency range, an intermediate plate (usually made of steel) and also an additional spacing absorbent layer may be inserted into the absorbing linings for test rooms, the performance such absorbing panels then being (partially) based on the effect of resonant membrane (also known as resonator).
In some cases, absorbent linings for test rooms are in the form of wedges (i.e.: pyramid-shaped subsets) while in other cases, compact absorbers or asymmetrical structured absorbers are used.
The prediction of the performance of plane absorbing linings for testing rooms can be performed with the simulation software SILDIS®®.
Verification of acoustic performance of absorbing linings for testing rooms can be made in accordance with ISO 354 Acoustics - Measurement of sound absorption in a reverberation room or in accordance with the standard NF EN ISO 10534-1 Acoustics - Determination of sound absorption coefficient and impedance in impedance tubes - Part 1: Method using standing wave ratio