Design of a new Sound Field Analysis Recorder (SOFAR) for isotropy quantification in reverberation chambers

This presentation describes the design of a new SOund Field Analysis Recorder (SOFAR) that will allow the quantification of isotropy in reverberation chambers used for standardized measurements of absorption coefficients. The device, placed in close proximity to the absorbing sample, enables an analysis of the directional properties of the sound field in the testing area, and a characterization of the distribution of acoustic energy arriving onto the sample. The measurement device consists of a movable gantry containing an array of 32 microphones, which can be automatically moved to scan the sound pressure field in a plane parallel to the absorber. The frame supporting the gantry can also be displaced along the vertical axis, enabling the collection of acoustic data in four parallel planes. The scanning procedure results in a total of 4,096 impulse responses measured in the volume above the test area. Based on the measured responses, the isotropy of the incident sound on the sample is determined using an isotropy coefficient described in [J. Acoust. Soc. Am. 143(4), 2514-2526 (2018)]. A prototype of the SOFAR is evaluated in a newly designed 285 m3 reverberation chamber and the industrial applicability of the device is discussed.