Calibration method of smartphones for environmental noise measurement

There was a wide demand for the use of smartphones in environmental noise measurement. However, due to the insufficient understanding of measurement influencing factors with smartphones and the difficulty in implementing calibration, smartphone measurement has not been widely used now. The calibration method of smartphones for noise measurement was discussed in this article. The comparison method with different ways was studied, including in reverberation room, in anechoic chamber, and in a closed calibrator, which was specially designed. The effects of influencing factors such as Apps, smartphones with different operating systems, smartphone postures in measurement, and sound indicators used in calibration were considered. Then the calibration methods were analysed through on-site comparing measurements of environmental noise. The results indicate that there was no significant difference of calibration accuracy between the environment of the laboratory and the simplified calibrator. The detailed factors in calibration deserved more attention. As some smartphones have significant deviations in high-frequency range, the spectrum correction was necessary. With spectrum correction, the bias of measured values between smartphones and the standard sound level meter was relatively acceptable. With an appropriate calibration method, smartphones have high potential for application in large-scale participatory measurement of environmental noise.