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Automatic measurement device for low-frequency sounds

Automatic measurement of low-frequency sound from aircraft operation

Low-frequency sounds from helicopters and other rotary-wing aircraft and propeller-driven aircraft have been the focus of much attention in recent years. Although indicators for evaluating the health effects of low-frequency sounds are yet to be developed, complaints seemingly caused by low-frequency aircraft sounds have been received.
Automatic measurement devices for low-frequency sounds incorporated into automatic measurement devices for aircraft noise allows for long-term, hands-free measurement of low-frequency sounds generated by aircraft. Moreover, the automatic measurement device for low-frequency sounds includes an automatic identification function for rotary-wing and propeller-driven aircraft--which contain many components associated with low-frequency sounds--, combining acoustic and statistical analyses in order to distinguish between noise generated by jet planes or helicopters and to automatically detect operation of Osprey aircraft, which has drawn much attention in Japan recently.

Aircraft identification technology based on low-frequency sounds

Pre-adjustment:
Acoustic analysis of previously recorded sound waveforms (actual sounds) from individual aircraft models make it possible to extract characteristic low-range frequency components (acoustic data) and to create a database for each model. These databases are then optimized through individual statistical analysis, from which a prediction model for each type of aircraft can be created.

Automatic measurement:
The sound waveforms (actual sounds) of generated low-frequency sounds are captured and acoustically analyzed in order to extract the characteristic low-frequency components (acoustic data). The prediction probability values for each model are then calculated by applying this analysis to the predication model for each aircraft type. In an automatic measurement device for low-frequency sounds, measurement data from a low-frequency sound pressure level meter (for example, a 1/3 octave band sound pressure level or a G-characteristic sound pressure level) are collected as digital values every second. Prediction probability values for each model are also calculated in real time every second and are continuously recorded. For more information, please see our technical newsletter, No. 40.

Analysis and evaluation of low-frequency sounds

Using dedicated aggregation software, analysis and evaluation of measurement results from an automatic measurement device for low-frequency sounds are possible. This software makes it possible to display any observed aircraft noise together with data such as reference values from the Ministry of the Environment regarding material and physical/emotional complaints on a graph showing 1/3 octave band sound pressure levels or G-characteristic sound pressure levels. Such a graph allows for intuitive confirmation of whether the observed sound exceeds the reference values. The software also makes it possible to display this data alongside the automatically identified model information. The number of seconds in excess of the reference value or other data set can also be aggregated for each frequency and output as a daily report.

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