Safe and Sound
Over time, automobiles have become ever safer. Airbags all around us protect us against impact and crumple zones keep the impact away from the people in the cabin. In more modern developments, automobiles are surrounded by sensors and even cameras to warn the driver about nearby objects and even drifts across traffic lanes. And today’s post-modern vehicles will even apply the brakes upon sensing danger. Even after all of these advancements, accidents happen.
As safety technology in automobiles has improved, so has the probability of surviving a car crash. Unfortunately, one of the adverse outcomes of a car accident is often a hearing loss, induced by the loud sounds associated with the impact, the crumbling of metal and glass, and airbags deploying. An air bag deployment can generate between 160 and 180 dB SPL of transient sound—certainly enough to create sensorineural or mixed hearing loss.
The latest generation of safety technology has begun to focus on sensing when an accident is inevitable and triggering a series of tools, actions, and warnings to limit the effects of the collision on the occupants of the car. Mercedes-Benz calls its suite of technologies that are activated in anticipation of a collision PRE-SAFE®. For example, upon sensing a collision, the reversible seat belt tensioners are deployed in 150 ms, literally almost as quickly as an eye blink (100 ms in humans).
Mercedes-Benz just added a new feature to its PRE-SAFE® suite to save the occupants’ hearing. Upon sensing an inevitable collision, the car plays a pink noise at approximately 80 dB SPL to trigger a stapedial reflex. They call it PRE-SAFE®Sound. Just the idea to use biology (reflex) to protect biology (hearing) is bright enough. However, the important piece of this solution is in the use of pink noise. Using a tone, as we often do, to measure acoustic reflex thresholds would have required higher levels that Mercedes engineers deemed to be too loud for the car. Switching to pink noise solved the problem.