Evaluation of smartphone sound measurement applications using external microphones—A follow-up study

Abstract

The National Institute for Occupational Safety and Health (NIOSH) conducted a follow-up study to examine the accuracy of smartphone sound measurement applications (apps) using external, calibrated, microphones. In the initial study, we examined 192 apps on the Apple (iOS) and Google (Android) platforms. Overall, 10 iOS apps met our selection criteria for occupational noise exposure measurements, and of those, only 4 iOS apps (SoundMeter, SPLnFFT, SPL Pro, and NoiSee) were within ±2 dB(A) of a reference microphone. For this study, we selected the same 4 iOS apps and examined their accuracy and performance using the MicW i436 and the Dayton Audio iMM-6 external microphones. The MicW i436 microphone is marketed as compliant with IEC-61672 class 2 sound level meter standard. Testing was conducted in a reverberant chamber using pink noise over seven nominal sound levels from 65 to 95 dB. The results showed an even closer agreement than the earlier study, with mean differences within ±1 dB(A) of the reference microphone. This study suggests that the use of external microphones, and the ability to calibrate the microphones and apps, improves the overall accuracy and precision of measurements, and removes many of the constraints and limitations associated with the built-in smartphones’ microphones.