Smith, A., "Accuracy and Limitations of Using an iOS Device for Noise and Vibration Measurements," SAE Technical Paper 2015-01-2283, 2015, doi:10.4271/2015-01-2283.
iOS devices, including iPhones and iPads, are being used increasingly for professional and scientific applications. Using an iOS device for noise and vibration measurements is an application with many advantages, given its small size, availability, cost, and ease of operation. A system for measuring noise level, logging noise over time, doing FFT frequency analysis of sound, and measuring speech intelligibility has been created. This platform has been developed to use either an iPhone or iPad as a host device. This provides a portable, cost-effective and easy to deploy test and measurement system.The main area of system performance concern is the transducer. The typical transducer in an iOS device is designed with speech analysis in mind, rather than wide-band acoustical analysis. Additionally, the iOS device gyroscope has been optimized to recognize gross movement, rather than detailed fine movement.The strategy for addressing these set of issues has been two-fold. To address the issue of the limitation of the iOS device microphone, a set of optimization functions has been developed for the onboard transducer responses. To overcome this transducer limitation altogether, a set of professional quality external microphones and input devices that bypass the onboard transducers completely can be employed. The external transducer and ADC/DACs bypass the iOS device's analog electronics. This affords full control over the response characteristics, noise level, and dynamics.This dual strategy for data acquisition (either by using the internal transducers with optimization function or external transducers and electronics) gives the flexibility to either perform general-purpose measurements (using only the onboard transducers), or meet ANSI and IEC standards for Class 1 measurements.This paper demonstrates the operation of the system, discuss the accuracy and limitations of the hardware devices, and shows how it is possible to obtain either casual or reference-quality measurements using mobile devices.