Measurement Accuracy for Qualification Testing of Anechoic and Hemi Anechoic Chambers Using the Continuous Draw Method

Anechoic/hemi-anechoic chamber qualification testing is typically conducted by measuring the free-field response as a microphone is traversed away from a central noise source toward the chamber perimeter. Based on ISO standard 3745, the microphone can be moved either incrementally or continuously. If using broad band random noise, the measurement must last a sufficient period of time to ensure an accurate averaged level is recorded. For low frequencies this can require extended periods of time. Attempting to establish a microphone traverse rate slow enough to allow sufficient time averaging becomes tedious. Over distances of 3 meters, this can require a draw that takes 20 minutes or longer. This paper discusses techniques explored to produce results that are quicker and more accurate than by typically applied methods.