Title: The Design Considerations of an Anechoic Chamber
text: There are a number of factors that dictate the size, type, and resultant over all cost of a controlled acoustical environment in which measurements can be made accurately and reliably. The type of acoustical environment is generally specified in the appropriate SAE, ISO, ANSI or ASTM standards. The purpose of this paper is to concentrate upon the design considerations of a properly engineered anechoic chamber. Anechoic is defined as “free from echoes or reverberations”. An ideal chamber would contain no reflections of sound from its walls, ceiling, or floor and an acoustical free-field condition would exist. Probably the best testing environment is outside with no boundaries to cause reflections. However, temperature, pressure, humidity, and wind can significantly and unpredictably disturb the uniform radiation of sound waves. In an ideal free-field environment, the inverse square law would function perfectly. This means the sound pressure level from a sound source would decrease six decibels for each doubling of distance from the source. For anechoic chambers to function as required to meet the various standards, a number of acoustical, mechanical, electrical, and aerodynamic considerations apply. This paper is intended to briefly address these considerations which include some, or all, of the following: Test object size Anechoic treatment selection Cut-off frequency Test object noise levels Parent room noise levels Vibration isolation Ventilation system requirements Structural requirements Physical access requirements Lighting and electrical requirements Visual requirements Housekeeping requirements RF shielding requirements