Page 18 - Summer2017

Acoustical Measurements with Smartphones
nents, a smartphone-based system could be genuinely use- ful to a qualified professional but that there are enough po- tential pitfalls to make it difficult to generically recommend smartphone SLM apps to the general public.
Current Use of Smartphones
in Acoustics
Publications continue to surface highlighting acoustics-re- lated studies being performed with or for smartphones. A recent study took a look at the use of smartphones to in- troduce sound level measurement and the creation of sound maps to architectural acoustics students in Japan (Satoh et al., 2016). It was found that iOS devices and some Android devices offered sufficient accuracy for their needs and that the use of smartphones can help engage the students more deeply in their study. The Doppler effect was studied using smartphones in an educational setting at universities in Ger- many and Switzerland (Klein et al., 2014). Another study presented results from the measurement of room acoustics parameters using two iPhone models (Rizzi et al., 2015).
At the Salt Lake City meeting of the Acoustical Society of America in May 2016, a special session was held that was dedicated to the topic of noise measurements with mobile apps. Topics presented in that session included the use of smartphones for assessing noise exposure for preterm in- fants while being transported by helicopter to neonatal in- tensive care units (http://doi.org/10.1121/1.4950019); re- mote monitoring of noise levels in hospitals and industrial plants (http://doi.org/10.1121/1.4950018); and measuring noise exposure levels in exercise (indoor cycling) classes (http://doi.org/10.1121/1.4950021).
Although published research featuring smartphones for acoustical measurements seems to just be getting started, hundreds, perhaps thousands, of apps are already available from numerous developers for accomplishing a broad array of acoustics-related measurement and analysis tasks. The traditional functions of a benchtop dynamic signal analyzer, including time waveform monitoring, single or multichan- nel spectrum analysis, transfer function and impulse re- sponse measurements, and coherence and cross-correlation measurements, can be made with a smartphone, a suitable app, and, if necessary, external adapters or accessories. Apps related to music (tuners and recorders), speech (pitch and formant analysis), and audio (electroacoustic system tun- ing and equalization) have been available in smartphone app stores almost since the very beginning of the modern, touch-enabled smartphone era.
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Present and Future Outlook
Although the notion of making acoustical measurements with smartphones is sometimes met with reasonable skepti- cism, evidence is growing to show that, by carefully selecting a device, an app, and a measurement microphone, even very accurate measurements can be made with a fairly high level of precision. The various components in the signal path and the potential for those components to change from day to day (particularly with software) require careful attention not only to see that accuracy is obtained initially but that it is maintained over time.
Regardless of the present inability of the smartphone to re- place a type 1 SLM, there are other practical benefits to the use of sound measurement or analysis apps. These include promoting public awareness about the potential dangers of high noise exposure; making ballpark measurements to es- tablish a need for more sophisticated measurements; iden- tifying frequency components of desirable sounds or un- desirable noises; educating students or the general public regarding basic sound measurement and analysis principles; and other personally or professionally beneficial activities.
The availability and capability of acoustics-related smart- phone devices, accessories, and apps continue to expand, which suggests that exciting and accessible new tools will continue to emerge in the years ahead. The possibility of carrying an acoustical measurement suite in your pocket, with minimal added cost relative to that of the smartphone already there, is compelling for many.
Biosketch
Benjamin Faber studied acoustics at Brigham Young University (BYU), re- ceiving a BS degree in electrical engi- neering and a MS degree in physics. Ben worked on energy-based active noise control both as a student and as a faculty research associate in BYU’s Department
of Physics and Astronomy until November 2006 and is co- inventor on five awarded patents stemming from his work there. Since then, Ben has been fully engaged as owner of Faber Acoustical, LLC, which specializes in developing in- tuitive software applications (apps) for performing real-time signal analysis, measurement, and data acquisition, particu- larly for Apple’s macOS and iOS.