Large Anechoic Chamber

Photograph: The Large Anechoic Room at ISVR.

The large anechoic room at ISVR
Photo courtesy Filippo Fazi, Fluid Dynamics and Acoustics Group

An anechoic chamber is a room in which the walls, floor and ceiling are lined with sound absorbing material, usually foam or glass-fibre wedges. The lining prevents the reflection of sound from the room boundaries so that ‘free-field’ conditions exist. The room sounds very ‘dead’. Sound measurements are not influenced by the room surfaces, and an anechoic room is an ideal environment for many standard tests such as the measurement of the sound power of a machine, or measurements of microphone and loudspeaker frequency responses.

The Large Anechoic Room at ISVR is one of the largest in the country. It was extensively refurbished during 1995/96 and the original polyurethane foam wedges were replaced with glass fibre wedges.

Construction
Built as a box within a box, it is acoustically isolated from the rest of the building and adjacent chambers by an air gap all around and is supported on vibration isolation mounts. The reinforced concrete walls are 305 mm thick.

Wall Lining
There are over 8,000 non-flammable glass-fibre cored wedges, extending 910 mm from the walls, floor and ceiling. Free-field conditions exist at frequencies above 80 Hz.

Dimensions
Without wedges the bare chamber is 9.15 m x 9.15 m x 7.32 m, volume 611 cubic metres. The usable space between the wedges is 7.33 m x 7.33 m x 5.50 m, giving a usable volume of 295 cubic metres
 
Access
Double doors 2.0 m wide x 2.4 m high
 
Flooring
A grid of removable floor panels can support a spread load of several tons with a minimum of interference with the anechoic nature of the chamber. An optional floor of varnished chipboard is available for measurements requiring a free field above a reflecting plane (hemi-anechoic conditions).

We have produced a brief guide to the ISVR Rayleigh Laboratory test facilities, which can be downloaded and printed. It gives a description of the facilities, including the Large Anechoic Chamber, with photographs showing access routes and dimensions.  The guide is intended to assist clients wishing to test large pieces of equipment.

 Download guide to test facilities in pdf format (316 KB).