The Ride On magazine of Australia has found that cyclists listening to music or podcasts with headphones hear more ambient noise than motorists who don't have their radios on (photo above is courtesy of Ride On). This innovative investigation by Ride On revealed that the reality if contrary to a popular misconception - commonly held by police and insurance companies with no evidence - that cyclists are riding dangerously if they wear headphones.
Ride On used a synthetic "ear" to measure the volume inside and outside the car.
"With the ear-bud in our synthetic ear but not playing music, we measured the ambient traffic noise at 79dB. With the in-ear earphones, the traffic noise was 71dB," found Ride On. The volume was set to a "reasonable" level, about 3 clicks below full volume on the iPod, which they measured to be 87 dB. They then had a cyclist call out "Passing" and ring a bell. The tester outside the car with headphones on playing music heard the call, whereas the tester in the car with the motor running and the stereo on at a moderate level (69 dB) did not.
We quickly established that cars are remarkably soundproof. We measured the average peak of ambient traffic noise inside the car (with the motor running) to be 54dB, which is 26dB quieter than outside the car. We rang a bike bell right outside an open car window and measured it from in the car at 105dB. With the window closed, the same bell registered just 57dB.
The decibel is a logarithmic unit, which means that the difference increases as the decibels are higher. On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB. Normal conversation is around 60 dB and a lawn mower around 90 dB. Thus ambient sound inside the car is about 100,000 times that of silence and the ambient sounds outside the car, even with headphones, are about 10 million times.
There are two things I take away from this: one, that riding with headphones are fine so long as the volume is reasonable, and, two, a cyclist is better off being prepared to stop or serve rather than ring a bell at a motorist with their window closed.