Filtering the reflection waves from wedges of an anechoic chamber for microphone free-field sensitivity calibration

For the Laboratory Standard microphone sensitivity calibrated in free-field theme, the reflection of sound waves is an imperative disturbance. The perfect absorption coefficient of wedges overlay in an anechoic chamber are desired to be one. In reality, the slight geometric differences between wedges causes the variant absorption curves, thus the reflection waves should not be occur in the chamber. The pure tone emitted from the transmitter microphone during calibration is therefore mixed with phase shifted reflection waves and accompanying standing waves. Therefore, the technique of filtering the reflection and standing wave during the calibration of microphone sensitivity become an important work. A method to deal with the reflection wave by data processing is presented in the article. The difference between the filtered result and output from free-field calibration system in ITRI/CMS shows a difference between ±0.08 dB in the free-field calibration.