Anechoic Chambers

What is an Anechoic Chamber?

IAC Acoustics offers both Anechoic and Hemi-anechoic chambers.  Anechoic rooms are fully lined with anechoic wedges, including the floor, to create a specific controlled test environment for professional acoustical testing.  Hemi-anechoic rooms are of the same design and configuration, however they are equipped with a sold floor, to facilitate the testing of large and heavy objects whose typical application would be on a reflective pane. Both test facilities allow for precision acoustic testing to benchmark research and product development to ISO measurement standards.

An anechoic chamber can be considered similar to a precision acoustical measurement instrument, providing a free-field environment without noise interference or sound reflection. In an ideal free-field environment, the inverse square law would function perfectly. This means that the sound level from a spherically radiating sound source decreases by 6dB for each doubling of distance from the source. For a free field to exist with perfect inverse square law characteristics, room boundaries must have a sound absorption coefficient of unity at all angles of incidence. In practice this is usually not quite perfect and deviations from the inverse square law are to be expected.

Construction of Anechoic Rooms

For anechoic rooms to function well, a number of acoustic, mechanical, electrical and aerodynamic considerations apply. These will include some, or all, of the following:

Anechoic Wedges

One practical well proven method to achieve a free-field is to shape sound absorbing material into wedge configurations for mounting on to the interior surfaces. The wedge shaped geometry ensures a gradual change in the acoustic impedance of the transmission media, ensuring that sound waves are absorbed by the material, rather than reflected at an interface. The effectiveness of the absorption depends on the geometry and materials used. The lowest frequency at which the absorption is effective (cut-off frequency) is inversely proportional to the depth of the wedge. IAC’s own impedance tube is used for critical adjustment of wedge dimensions before finalising each design. Due to variations in material characteristics, statistical quality control measures are employed during wedge production to ensure specified acoustic performance.

Satra Technology

Formed in 1919 SATRA helps manufacturers and suppliers to evolve by providing technical knowledge, research and testing. Currently commissioned for testing various PPE items such as high visibility clothing, footwear and protective eyewear, SATRA wanted to be able to offer testing of hearing protection to their portfolio. In order to certify, test and develop products such as ear defenders for various manufacturers, an anechoic chamber was required.  You can view a time lapse of the chamber build here:

“The new hemi-anechoic chamber will help to widen the range of services SATRA is able to provide, not only for hearing protectors, but hopefully other products in the future. Overall the project ran very smoothly and the new chamber performs very well.”

Andy Todd, SATRA Acoustic Engineer