Acoustic Anechoic Chamber (INMS)

The acoustic anechoic chamber is a testing facility intended to reproduce acoustic free-field conditions in a controlled environment. Its associated instrumentation permits accurate measurement of the spatial radiation patterns of loudspeakers and the directional receiving characteristics of arrays of microphones.

The chamber consists of an outer shell of concrete block and reinforced concrete surrounding an inner room of steel-panel construction which is mounted on springs to isolate it from the effects of vibration. The walls inside the chamber are lined with fiberglass wedges with a square base measuring 61 cm on each side and 82 cm in length. The available space inside the chamber measures 5.8 m in length, 3.7 m in width and 3.4 m in height. The walls of the chamber absorb 99% of all incident acoustical energy within the design frequency range and the noise due to external sources is below the minimum audible field. Measurements of the decrease in sound intensity with distance reveal negligible deviations from inverse square law behavior above a frequency of 100 Hz.

The chamber is equipped with an array of calibrated sound pressure microphones, turntables, and a full instrumentation suite. For specialized measurements, numerous hangers are provided throughout the chamber for suspending test equipment and there is a removable floor to provide access to the entire space inside the chamber. Air-handling units provide a supply of fresh air to the chamber while maintaining noise below the minimum audible field.

Policies and Procedures for Services

Related Information

Policies and Procedures for Services

Institutes:

• NRC Institute for National Measurement Standards