Using Cell Phones to Make Noise Measurements
Twice in the last month, we have heard “I just used my cell phone to make noise measurements so you do not need to make measurements.” Mobile phone sound meter applications have added a new twist to our consulting services. As for using our smart phones as sound level meters… The standard phone, as delivered from Apple, Motorola, Samsung, etc. is an awful sound level meter that should not be used for anything other than fun! Of the over 120 and growing sound meter applications currently available, none of them make up for the inexpensive microphone that is part of the phone. The microphone elements we use cost hundreds of dollars, much more than the most expensive smart phone available. The meter that this very expensive microphone element attaches to is even more costly.
When the iPhone first came out, one of our colleagues was doing a demonstration to a city council. The demonstration was a recorded simulation of a noise event. Prior to the meeting he carefully adjusted the demonstration level in the council chambers, in order to show the most accurate information. At the time of the testimony, our colleague reproduced the calibration level and showed the council members that it was 60dBA – the goal for the calibration level. Then two different council members that had just gotten their iPhone for the holidays said, no I read it at 64dBA here and the other said no it is only 57dBA here. How do you argue with Apple? They clearly would not make a product that was not accurate.
In April 2014, the Journal of the Acoustical Society of America published an evaluation of smart phone sound measurement applications. In this article, authors Kardous and Shaw tested a number of different systems and apps. Their research confirmed this disparate range of readings reported when the devices are side-by-side in the same sound field.
A few weeks ago we tried a similar test… we used our sound masking system to create a uniform sound field as defined by our “true test meters”. We used three of our “test meters” to triple check the levels and all were within a few tenths of a decibel, as we would expect. Unfortunately, our smart phones had a 10 decibel range between the lowest and the highest and none of them matched what our “true test meters” reported.
Is there a use for the smart phone sound meter app? Sure, it gives you an idea of the relative level. How loud is the office relative to the kitchen at home, or how loud is my car with the windows rolled up at a stop light. Beyond that, be very careful of what you read on the web about acoustics, and what someone claims (and how they claim it) when it comes to a noise level measured by their smart phone.