Failure diagnosis of sound level meter in automatic aircraft noise measurement devices

(1) Around airports, many sound level meters (SLM) are installed, and continuous measurement is conducted for obtaining noise data. Usually, these SLM are inspected periodically, typically semi-annual or annual basis. However, it is difficult to identify the timing of the defect of microphone is happening, because its progress is caused gradually. (2) This issue always happens if the only one microphone is used. In this paper, we proposed to install an additional microphone close to the microphone of SLM and recorded the sound simultaneously. And we tried to detect the timing of microphone defect, especially dropping microphone sensitivity, the metric based on coherence between two signals and sound pressure level differences. (3) We verified the difference between SPL at several frequency bands and overall SPL from the data measured with a sound level meter as well as with an additional microphone simultaneously. With this technique, we found it is possible to detect the sensitivity change with exceeding 0.5dB from the time of annual inspection, even though considering fluctuations due to background noise. (4) The proposed method is useful for detecting sensitivity drop of SLM's microphone remotely, without conventional inspections.