Impulse response characterization of anechoic and hemi-anechoic chambers.

Characterization of a measurement environment is an important component of assessing measurement uncertainty. The traditional technique in anechoic and hemi-anechoic chambers is qualification through draw-away testing: deviation from square-law spreading is estimated along various radials, for broadband noise and occasionally for tones. All locations within a volume for which the deviations are below certain criteria are considered “qualified” for testing, and measured results from these locations are typically not corrected for the influence of the room. The draw-away test is tedious and time consuming and does not yield the information that is actually desired: precision of measurements for a particular source-receiver pair. Impulse response methods are considerably more rapid and provide a wealth of information in postprocessing including amplitude, phase, and time-delay factors for both steady-state and transient sounds, across arbitrary frequency ranges. This paper will explain how the impulse response characterization can be obtained and how it can be used to improve precision of measurements in anechoic and hemi-anechoic environments.