To App or Not to App?

Following the Development of Sound Level Meter Apps

The smartphone is one of the technological developments that has taken the world by storm over the last decade. Statistics released in June 2016 forecast the number of smartphone users to grow from 2.1 billion in 2016 to around 2.5 billion in 2019, with just over 36 percent of the world's population projected to use a smartphone by 2018. In addition, app downloads reached nearly 200 billion in 2017 and are expected to reach over 350 billion by 2021.


It is no surprise, then, that the smartphone is cited by many industrial hygienists as their favorite piece of work equipment. Industrial hygienists can use smartphones to make notes and take photographs while on site, email measurement results to colleagues, access websites for guidance, and even make the occasional phone call.


We’ve Got an App for That?

It should also come as no surprise that there are hundreds of sound level meter apps available. As a manufacturer of professional sound level meters, Casella urges users to exercise some caution (we would say that, wouldn’t we?). But we don’t want to appear Luddite in our actions. (The Luddites were a radical group of English textile workers in the 19th century who destroyed weaving machinery that they believed was threatening their jobs. This was a form of protest against the use of machinery in a "fraudulent and deceitful manner" to get around standard labor practices.) Buying instrumentation that claims to meet a standard is already a case of “buyer beware.” Products often only get “found out” when tested by a capable, ISO 17025-approved verification laboratory.


Indeed, there are many benefits of using an app with common tools of the industrial hygiene trade. For example, apps used with noise dosimeters or personal air sampling pumps can warn of low battery or a failed measurement and can run remotely from a discrete distance without having to disturb the worker. This improves the productivity of both the industrial hygienist and worker alike; there is nothing worse than having to repeat a measurement or miss a once-in-a-blue-moon opportunity.


A Look at NIOSH’s App

The NIOSH Sound Level Meter app is one such potentially game-changing development. Its objectives are to be applauded; the app raises awareness of noise among workers and also draws attention to the need to control the use of such apps. To be compliant, NIOSH points out that users need a phone with an external microphone capable of being field calibrated for microphone sensitivity (using an equally compliant acoustic calibrator).


NIOSH was quite right to go down the iOS route because the accuracy of many Android phones cannot be guaranteed. However, the agency’s development may be short-lived given the lack of an external socket on new iPhones. Plus, there are many places where workers and visitors are not permitted to use a mobile phone for security or safety reasons (for example, in hazardous atmospheres that require devices to be intrinsically safe).


In an update published on the NIOSH Science Blog in June 2018, the agency stated that “researchers have evaluated the [NIOSH] app’s performance as part of a system (iPhone + external microphone) for compliance with type 2 requirements of IEC 61672/ANSI S1.4 standard Sound Level Meters – Part 3: Periodic Tests,” and that the results were published in the journal Applied Acoustics. The article abstract states:


Smartphones have evolved into powerful devices with computing capabilities that rival the power of personal computers. Any smartphone can now be turned into a sound-measuring device because of its built-in microphone. The ubiquity of these devices allows the noise measuring apps to expand the base of people being able to measure noise.


Many sound measuring apps exist on the market for various mobile platforms, but only a fraction of these apps achieve sufficient accuracy for assessing noise levels, let alone be used as a replacement for professional sound level measuring instruments.


In this paper, we present methods and results of calibrating our in-house developed Noise sound level meter app according to relevant ANSI (American National Standards Institute) and IEC (International Electrotechnical Commission) sound level meter standards. The results show that the sound level meter app and an external microphone can achieve compliance with most of the requirements for Class 2 of IEC 61672/ANSI S1.4-2014 standard.


This begs the question: is meeting “most of the requirements” good enough, and do you want to expand the base of people who are able to make measurements? The acid test for the app would be a full type approval as required, for example, in Spain, where—under a quirk of their legal metrology legalization that applies to weighing scales and taxi meters, among other things—sound level meters, noise dosimeters, and acoustic calibrators are required to be type approved before being put on the market (with a substantial penalty for breaches). Notwithstanding the instrument compliance issue, there are all kinds of measurement do’s and don’ts that users have to be aware of. Sometimes, training or professional certification is required.


Upping the App Game

Now that the “genie app” is out of the bottle, perhaps it is time to consider resurrecting the Class 3 indicator grade that existed in long-forgotten ANSI and British standards of the 1970s. This would be fair to instrument manufacturers who spend hundreds of thousands of dollars on product development as well as in-house and third-party verification testing for Class 1 and 2 compliance. Data from a Class 3 instrument would be inadmissible in support of a claim for noise-induced hearing loss, but it would be useful for the intended purpose of the app: increasing awareness for the 30 million American workers who remain at risk from damaged hearing. (Let us not forget what is really important here!)


For their part, professional sound level meter manufacturers need to up their game. There are plenty of us around to ensure healthy competition and compliance, which in turn leads to innovation and increased customer value.



Applied Acoustics: “Smartphone-based sound level measurement apps: Evaluation of compliance with international sound level meter standards” (October 2018).

Health & Safety Matters: “Day in the Life of …"

NIOSH: NIOSH Sound Level Meter App (August 2017).

NIOSH Science Blog: “So How Accurate Are These Smartphone Sound Measurement Apps?” (April 2014).

Spanish Royal Decree 889/2006 and ORDER ITC/2845/2007 (PDF), which regulate the metrological control of the State of the instruments intended for audible sound measurement and acoustic calibration (translation).

Statista: “Number of smartphone users worldwide from 2014 to 2020 (in billions)” (June 2016).

Tom’s Guide: “The New iPhones Have Truly Killed the Headphone Jack” (September 2018).?