Mercedes-Benz is trying to cut down on hearing damage caused by the deafening crunch of a car crash, and it's doing so by blasting pink noise through the stereo when you're about to hit something, to trigger a fascinating physical response.
Mercedes-Benz has done a lot to push automotive safety forward over its long history. In 1978, the S-class offered the first (or one of the first, depending on who you ask) 4-wheel ABS systems on a production car. In 1987, along with BMW and Toyota, Mercedes put the first traction control systems into production cars.
More recently, in 2003, the company introduced its Pre-Safe system, a series of measures that kick in when the vehicle detects what it decides is an inevitable crash. Seat belts quickly tension to an optimum point, windows and sunroofs close, the seats puff up to stabilize the bodies in them, and in some cases they even move slightly toward the center of the car before impact.
And for 2016, proving these guys really do think of everything, a system to protect your ears from hearing damage that could be caused by the sudden, deafening crunch of a car crash has been introduced.
The Mercedes-Benz team decided to protect against this by triggering a reflex in the body known as the acoustic reflex, or stapedius reflex – an involuntary muscle contraction in the middle ear that effectively dampens the vibrational energy that's transferred to the cochlea.
When the stapedius muscle flexes, it pulls on the stirrup bone in the middle ear, weakening the connection between the eardrum and the inner ear, so that some proportion of the sound is reflected back out through the eardrum without reaching the inner ear. It takes about a tenth of a second to kick in, so it wouldn't normally protect you from a loud, sudden sound like the impact of a car crash.
Normally, this reflex is triggered by loud sounds or vocalization, but researchers have found that presenting more than one tone at once can trigger the effect at a lower sound volume.
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. That 80 decibel level isn't even an uncomfortable volume, but it's enough to trigger the desired acoustic reflex just before the crunch of impact.
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.
Pre-Safe Sound is rolling out as of this year on the E-Class, and will presumably be implemented in other cars with the Pre-Safe system in coming years.
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