Acoustic Chambers and Rooms

There are a number of different types of acoustic chambers and rooms. Some are defined very specifically and others more loosely. These rooms are mainly used by noise and vibration measurement specialists.

Acoustic chambers and rooms are quite specialist rooms to design, build, operate and maintain. Often the design of these rooms will be done by specialist design acoustic design companies.

Anechoic Chamber

anechoic chmaber

Literally meaning “without echo”. A room whose boundaries effectively absorb all incident sound over the frequency range of interest, thereby creating essentially free field conditions. This allows measurements to be made without them being contaminated with reflected waves from the walls, ceiling and floor.

Rooms of this type are used to test audio equipment such as loudspeakers and microphones and for other types of research.

A secondary wire mesh floor in the middle of the room is often used When larger objects need to be accommodated.

Reverberation Room

Room having a long reverberation time, specially designed to make the sound field therein as diffuse as possible. This is normally a room with hard walls, either concrete or heavy plaster. This room can then be used to measure the absorption coefficient of materials that are brought into the room.

Semi-Anechoic Chamber

semi-anechoic chamber

A room which creates free field conditions but above a reflective plane.

Above a certain frequency all sound waves that hit the walls or ceiling of the chamber will be absorbed.

This type of chamber is normally used in vehicle testing with a rolling round so that the vehicle may be driven. The semi-anechoic chamber then forms a controlled environment with the surrounding acoustic conditions behaving as a sterile version of the real world. In this way accurate measurements of the sound inside and outside the vehicle can be made under operating conditions.

References

  1. ISO 354 Acoustics/Measurement of Sound Absorption in a Reverberation Room
  2. ISO 3741 Determination of Sound Power Levels of Noise Sources – Precision Methods for Broad-Band Sources in Reverberation Rooms
  3. ISO 3742 Determination of Sound Power Levels of Noise Sources – Precision Methods for Discrete-Frequency and Narrow- Band Sources in Reverberation Rooms
  4. ANSI S12.32 Determination of Sound Power Levels of Discrete-Frequency and Narrow-Band Noise Sources in Reverberation Rooms
  5. ASTM C 423 Standard test method for sound absorption and sound absorption coefficients by the reverberation room method.

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