Photo credit: Sara Star NSlicensed under CC BY-SA 2.0

By David M. Sykes, Vice Chair, Quiet Coalition

Oct 1, 2019

For those of us who’ve been working for decades on the tough problem o
f noise in hospitals—specifically the effects of that noise on patients, physicians, families, and staff—news that the Robert Wood Johnson Foundation supported the work of popular podcast  99% Invisible’s inquiry into this problem begets mixed emotions. Finally, major foundations are listening!

Believe me, we welcome their interest! What better place to study the effects of noise on human health than in hospitals? If any professional group is able to carefully examine health effects and tease apart causality, shouldn’t it be medical professionals, both clinicians and researchers?

My colleagues and I have been enthusiastic about working with hospital staffs on noise and health for 18 years now. But frankly, it’s been extremely difficult to find foundations and government agencies willing to fund this kind of trans-disciplinary work. Why? Because it’s expensive and hard to assemble a team of researchers drawn from several different disciplines like medicine and acoustical science–the two groups barely speak the same language. But one of our proudest efforts did just that, the so-called Harvard Sleep Study, and it has become important because of its rarity.

That study, which began in 2006 and was published in 2012, discovered and described something we all know intuitively: that individual sounds, like musical notes, or alarm noises, or mechanical equipment or passing aircraft, are very different from each other and can’t be described with a single metric like the decibel rating. Indeed, the ability of a particular noise to arouse you from sleep depends more on the characteristics of that sound, rather than it’s decibel rating.

The decibel rating scheme records only sound-energy levels—that’s the energy that can physically harm your ears and your auditory system. But the decibel rating scheme does not, and indeed cannot, account for other noise effects such as a stress reaction, which can lead to cardiovascular problems or annoyance.  For example, a neighbor’s barking dog, a passing aircraft, or someone using a leaf blower near your house may be very annoying and may even disrupt your sleep, but is it loud enough to harm your hearing?

So it should come as no surprise that there is an alternative approach to measuring the many effects of noise. This alternative approach, called psychoacoustics, has been around nearly as long as the decibel rating scheme, but while it’s been embraced outside the U.S., it has had virtually no effect in this country. Psychoacoustics, also called supplemental metrics, emerged in the U.S. seven decades ago, but then emigrated to the European Unon. The classic work in this field is called “Psychoacoustics” by Fastl and Zwicker.

In the U.S., work on psychoacoustics had virtually no effect on the field of noise control until last year, when Congress included a requirement in the Federal Aviation Administration Reauthorization Act that the Department of Transportation and the FAA begin using alternative metrics in their evaluations of the effects of noise on people in neighborhoods under airport flight paths.

If you’ve installed a free sound meter app on your smartphone, all you can measure is decibels (dB). At best you might be able to measure decibels with different weightings, e.g., dBA, dBB and dBC (the A, B and C versions adjust the dB scale to approximate human hearing or other dimensions of sound). But if you own a professional sound level meter, you can probably choose either one of the decibel scales, or an alternative called Sone. Do decibels and Sone measure the same things? in a word, no. Psychoacoustics measurements account for a variety of different aspects of sounds well beyond sound pressure levels.

The difference is as great, for example, as using a thermometer to take your body temperature versus using standard instruments to collect all of your vital signs and take a sample of your blood. That thermometer that takes your body temperature is a single indicator. The rest of your vital signs are something else entirely.

It’s exciting that the Robert Wood Johnson Foundation funded a podcast that considers metrics beyond decibels and considers some of the other vital signs that determine how the hospital soundscape affects patients and staff. Curiously, the researchers cited in this podcast don’t appear to be aware that there is already a well-defined, long-established set of metrics for doing so. One hopes they are not wasting time—and a foundation’s money–“reinventing the wheel,” ignoring the methods developed over many decades in the field of psychoacoustics.