“Pink Noise” Could Save Hearing In Crashes

Credit: DaimlerChrysler AG

Think car crash injuries and you probably think concussion or whiplash. But Mercedes-Benz wants to tackle another risk: hearing damage caused by the sound of the impact.

IEEE, which spotted an upcoming “Pre-Safe Sound” feature in a new car range, notes that a crash can produce sounds inside the car of 145 decibels, which can cause damage. To make things worse, the sound of an airbag going off can be as much as 165 decibels, similar to a close-range shotgun blast and in the range that could cause permanent hearing damage. Around one in six people who are sitting in front of a deploying airbag are thought to suffer some form of permanent damage.

In the first practical application of a concept patented 20 years ago, Mercedes-Benz plans to tackle that as part of its pre-crash safety measures. Those are the things a car automatically does in the few seconds between detecting a crash is imminent and the actual impact. They come ahead of measures such as deploying the airbags, which have to be timed for the moment of impact and come after steps such as tightening the seatbelt to reduce the chances of the driver or passenger being in a position where the airbag itself could hurt them.

The pre-safe sound will be around 80 decibels and consist of pink noise. Mathematically that means the “power spectral density (energy or power per frequency interval) is inversely proportional to the frequency of the signal.” In practical terms, it causes the middle ear’s stapedius muscle to tense up, thus reducing the strength of the vibrations passed through the ear.

It’s the same process that the ear carries out automatically just before you start speaking. In that situation it reduces the effective intensity of the sound of your voice by around 20 decibels, which is a comfort measure. With the cars, the idea is that a similar reduction could be enough to minimize both the damage and the chances of it being permanent.