When the car’s sensors sense an impending crash, the cabin is filled with a burst of “pink” noise, a broad spectrum of frequencies in which the power is inversely proportional to the frequency. If an impending collision is detected, the vehicle’s sound system plays a short interference signal, which can trigger a reflex, whereby the stapedius muscle in the ears contracts, which alters the link between the eardrum and the inner ear for a split second and better protects the inner ear against high acoustic pressures, which can result from a loud crash. To this effect, Mercedes-Benz engineers decided to use a short blast of pink noise – which basically combines all possible tones – in the seconds before impact, at 80 decibels, through the car stereo system.
– A coming safety feature for cars aims to protect drivers and passengers in a novel way: to save their hearing in a crash. The idea is that when a smartcar senses an imminent collision, the sound system sends out a burst of "pink noise" inside the car. That causes a muscle inside the ear to contract and thus protect the eardrum from the louder noise of the crash about to come, explains IEEE Spectrum. Mercedes-Benz is marketing it as "Pre-Safe Sound" in its newest E-class fleet. When a car crashes, the decibel level can easily reach 145, which is enough to damage the human ear. And that doesn't count the noise of the airbag deploying, which is even higher at around 165 decibels. The so-called pink noise is a safe 80 decibels, and it's enough to trigger what's known as the "acoustic reflex" to protect the ear. "Hearing loss is far from the worst damage a person can suffer from a car accident, but this is a cheap and simple way to reduce some of the human impact of road trauma, and a very cool idea," writes a blogger at New Atlas. Normally, the acoustic reflex takes about one-tenth of a second to kick in after a noise, not enough time to protect the ear from an instantaneous loud boom. The idea here is to trigger it early and safely. "A frequency spectrum known in physics as pink noise is ideally suited for this purpose," explains Mercedes in its own post on the feature. "It sounds like a bit like diffuse traffic noise, the breaking of waves or a waterfall." It's promising, but we'll have to wait for crash data to see whether it works as advertised, notes a post at BGR. (See Volvo's bold safety pledge.)