Sound level meter apps: Do they work?
With the growing popularity of smartphone apps, the newest way to measure sound level might be in your back pocket or purse. The latest statistics show that 71 percent of all people over the age of 18 own a smartphone; that means 171 million people have access to millions of apps. And with so many apps to choose from, it makes sense there would be one to measure noise levels. These apps aren’t just for fun; they are being used increasingly to measure occupational noise levels or noise in the workplace.
Hearing loss as a result of harmful noise in the workplace is a significant issue. More than 22 million workers in the U.S. are exposed to dangerous noise levels each year and there are over 20,000 cases of occupational noise-induced hearing loss (NIHL) reported each year alone. According to the National Institute for Occupational Safety and Health (NIOSH) guidelines for occupational noise exposure, recommended noise levels should be controlled at or below 85 decibels (dB) for eight hours. Many in noisy occupations are turning to sound level meter apps, or SLMs, for noise level information.
It might sound easy: just download an app, hold up your smartphone and have noise level information at your fingertips. But in actuality, sound measurement apps, in order to be effective in the workplace, need to meet certain criteria. Functionality, accuracy and relevancy to the user and to the specific work environment all must be considered.
So do they work? A team of scientists at NIOSH set out to find out.
In a pilot study, NIOSH tested a range of apps designed to measure noise level. Since Apple iOS and Android make up about 93 percent of the smartphones in use in the U.S., only iOS and Android apps and devices were considered for testing.
To begin, 130 iOS apps were considered, but only 10 met the criteria to be selected for the study. Out of 62 Android apps considered, four only partially met the selection criteria, As a result, no testing was done on Windows-based devices or apps.
The study was carried out in a reverberant noise chamber at the NIOSH acoustic testing laboratory using a range of 65 to 95 dB, in five dB increments, and at a frequency of 20 Hertz (Hz) to 20 kHz, which is the typical range of human hearing. The decibel level and frequency were chosen because they are reflective of typical occupational noise exposure. The results of the study, published in a paper in the Journal of the Acoustical Society of America, showed that only four apps were found to accurately measure noise levels to within two dB. These were:
The study wasn’t perfect, however. First, there was a limited number of devices tested in relation to what is on the market. Also, unlike a workplace environment, the reverberant noise chamber was a controlled noise environment, without factors like temperature, humidity, object interference and unstable equipment to affect noise level readings.
Although the numbers show that noise level measurement apps are gaining popularity, experts are not yet ready to consider the apps as a qualified substitute for traditional sound measuring devices. “They do not meet requirements for measuring occupational noise exposures,” said William Murphy, Ph.D., physicist at CDC/NIOSH and Hearing Loss Prevention Team leader. “If you’re using a smartphone, how do you calibrate it? That’s what it comes down to. Also, sound level meters need to go from 60 dB to 140 dB. While the NIOSH measurements are not hugely different, that’s a far cry from meeting type one requirements according to IEC standards.”
In the end, even though the apps are not perfect and not a substitute for traditional sound level meters or dosimeters, they might still have value. When used as a preliminary measuring device, the noise levels measured by the apps could be used to indicate whether a more formal monitoring program should be put into place. “You can use it to somewhat make an assessment and as an employee you could take that ... to see what the risks might be,” Murphy said.
Meanwhile the employer should be familiar with and take into consideration the noise levels of the machines in their workplace. Proper sound equipment, such as sound level meters and dosimeters, is relatively inexpensive and can be purchased or rented. Employers should also pay close attention to employee complaints about noise level, indications that employees are losing hearing or noise levels that make it difficult to hear conversation.
While sound measuring apps haven’t yet been improved to the point they can replace the more traditional sound measuring equipment, they have their place in improving awareness of workplace noise, encouraging employers to start hearing conservation programs and helping advance the hearing health of workers.