Lake Verynwy, Wales, Oct. 2017 | Photo credit: Dr. Daniel Fink
by Daniel Fink, MD, Chair, The Quiet Coalition
I recently wrote about measuring sound on an alpine hike, noting that the reading of the ambient noise level, which was in the low 40 decibels, was much quieter than we hear in our urbanized settings. I also noted that noise exposure, as part of the total daily noise dose, is what causes noise-induced hearing loss.
Another important adverse effect of noise–especially nighttime noise–is disruption of human activities, including sleep disruption. A measure of the noise impact on sleep is called the LDN, How quiet is it in a non-urban setting?
I hadn’t thought about this until last night. My wife and I are traveling in a remote part of Wales, staying at a hotel overlooking Lake Vyrnwy, a manmade reservoir supplying water to Liverpool 75 miles away. It took more than an hour of driving on one-lane country roads to get here. (It wasn’t that far, but at 25 mph, it took a while.) I woke up at night and realized how quiet it was: no sirens, no cars, no airplanes, no helicopters, no horn-based alerts when the neighbor’s son comes home from partying at 2 a.m. Curious, I fired up my Faber Sound Meter 4 app on my phone and measured the ambient noise at 33.7 C-weighted decibels. It was so quiet that the sound meter said there wasn’t enough data to report an A-weighted measurement. (I don’t understand the technical details of why this wouldn’t work.) Unweighted decibels measured 35.4.
Why is this important? Sleep disruption causes a stress response, a neuroendocrine response with increases in stress hormones and a parasympathetic nervous system response, with increased blood pressure and pulse. These involuntary physiological responses are what cause the increased morbidity and mortality reported from transportation noise exposure (and are discussed by Hammer, et al., and Basner, et al.). Yes, the experts think the evidence is strong enough to support a statement of causality, not just a statistical association or correlation. Even sounds as low as 32-35 decibels can disrupt sleep, causing microarousals as measured by EEG monitoring.
And now I know the answer to my question. How quiet should it be? At night the natural sound level should be under 40 decibels, probably under 35 decibels, and not urban nighttime noise levels of 55 to 65 decibels.