Acoustic Anechoic Chamber

Acoustical measurements under free-field conditions; chamber is designed to provide a highly anechoic sound field and a very small ambient noise level (acoustical and mechanical):

• Characterized frequency range: 40 Hz to 63 kHz
• Energy absorption: greater than or equal to 99% for frequencies greater than 45 Hz
• Inaudible ambient A-weighted sound pressure level less than -2 dB
• Vibration isolation: 52 springs, 3 Hz resonance
• Double shell construction, concrete walls 0.3 m thick
• Special multi-element wedge design; all six room surfaces covered by sound-absorbing wedges

Large multi-purpose facility; free-field volume between wedge tips of 450 m³ (10.0 m x 6.7 m x 6.7 m).

Wire mesh floor and adjacent control room for equipment setups.

Credit: NIST

Available for research-oriented or basic-characterization measurements of various electroacoustic devices, such as microphones, loudspeakers, and hearing aids:

• Sensitivity
• Frequency response
• Sound pressure level produced by sources
• Total harmonic distortion
• Directionality
• Self-noise

References

• W. Koidan and G.R. Hruska, Acoustical properties of the National Bureau of Standards anechoic chamber, J. Acoust. Soc. Am. 64(2), 508-516 (1978). 
• W. Koidan, G.R. Hruska, and M.A. Pickett, Wedge design for National Bureau of Standards anechoic chamber, J. Acoust. Soc. Am. 52(4)(Part 1), 1071-1076 (1972).