If an impending collision is detected that would be expected to produce a loud crash, the vehicle’s sound system plays a short interference signal. This causes the stapedius muscle in the ears to contract, which for a split second changes the link between the eardrum and the inner ear and so better protects it against high acoustic pressures. Most importantly, the reflex reduces the damage to hearing.
I might be imagining this, but I could swear I felt my ears becoming "full". Sort of like tired of the noise and numbing down? It's hard to describe but it felt similar to being on an airplane for a long time where sound becomes kind of dull because of all the engine noise.
It had no discernable effect on me, in a fairly noisy domestic setting including a washing machine in the background. I was expecting it to be much more penetrating.
Perhaps I've ruined my hearing after years of listening to shortwave white-noise.
You aren't if you use headphones and play it at close to 80db the feeling is like when you put on the active bose noise canceling heaphones and turn them on.
You feel a slight pressure on your ears which is what this intended to do.
I have read somewhere of a click being played through tanks' crews headphones when the main gun is fired, for this reason. This was wrt 70s-era Soviet tanks.
I wonder if it as cool hypothesis that they decided to implement as a cheap bit of marketing, or whether the protective factor is actually evidence-based.
A quick search on Google Scholar for "acoustic reflex noise" turns up this paper from 1962 which states in the abstract that the acoustic reflex is more easily triggered by wide bandwidth noise than a single sinusoidal tone. http://scitation.aip.org/content/asa/journal/jasa/34/9B/10.1...
I think we can safely say that this work is pretty evidence based.
Well, I read the marketing piece, yes - but thank you for pointing me at the evidence. The level of 'snark' may have been influenced by me previously reading the Soylent story. Marketing masquerading as science is certainly a thing, though not in this case.
A friendly reminder: "a quick search on Google Scholar" is not research.
That paper you mention is just a functional description of the "accoustic reflex". I don't think the parent comment was putting the existence of the "accoustic reflex noise" in doubt; rather, and I agree with him, it's its effectiveness to protect the driver in a car crash what is in doubt.
The page makes a reference to a human trial in 2011. It would be great if they included a footnote with the reference to the actual paper.
It’s not "research research" but it is "does this phenomenon actually exist in the literature" research.
Insisting on testing the phenomenon in an actual car crash seems superfluous to me. A car crash produces a loud noise that can potentially damage hearing, which can be alleviated to some extent by triggering the acoustic reflex with a quieter noise immediately before impact. So long as the generated noise is well below the threshold of damage then I’m really failing to see why more specific research is required in order to believe that this would be an effective intervention.
Yes, sorry - to be clear, I wasn't questioning the existance of the actual reflex. More the protective effect - however I understand that my post probably wasn't worded very well.
The bit about the noise from a car crash being loud enough to damage hearing after a one-time short exposure is what I doubt. Sure it's loud, but does a split second exposure to it really do permanent damage? I don't know what the answer is, but I am skeptical about the usefulness of this feature.
Stand by some one at the range without ear pro and ask them to shoot one shot.
The sound is only a fraction of a second but that ringing you'll hear is the death sound of the frequency you'll likely never to be able to hear again.
You also need to understand that sound and loudness isn't what causes hearing loss it's the pressure shockwave.
If a blast "noise" is mostly outside of your hearing range the pressure will still do permanent damage.
When a bomb goes off most of the energy can very well be outside of the normal frequency range of the human ear, it will still however rip your ears apart.
Well, consider that an air bag is basically a bomb going off in your face. And I'm pretty sure explosions from up close cause at least temporary hearing damage.
> Deployment of a driver’s side front airbag will generate mean peak sound pressure levels of approximately 160 dB (decibels).
> Studies have shown that the pain threshold from noise is about 140 dB and that a single exposure to sound pressure of this level can cause permanent, severe hearing loss.
> The deployment of a side airbag generates a mean peak sound air pressure of 178 dB.
So yeah ... a car crash will definitely mess with your hearing permanently.
According to the article Significance of the stapedius
reflex for the understanding of speech, the latency of
contraction is only about 10ms, but maximum tension may
not be reached for 100 ms or more.[6] According to the
article Le traumatisme acoustique, the latency of
contraction is 150 ms with noise stimulus which SPL is
at the threshold (ATR), and 25-35 ms at high sound
pressure levels. Indeed, the amplitude of the
contraction grows with the sound pressure level stimulus. 10]
Because of this latency, the acoustic reflex cannot
protect against sudden intense noises.[10][6] However,
when several sudden intense noises are presented at a
pace higher than 2–3 seconds of interval, the acoustic
reflex is able to play a role against auditory fatigue.[10]
I did not bother to check more than the abstracts of the references, but it does seem like evidence exists.
If an impending collision is detected that would be expected to produce a loud crash, the vehicle’s sound system plays a short interference signal. This causes the stapedius muscle in the ears to contract, which for a split second changes the link between the eardrum and the inner ear and so better protects it against high acoustic pressures. Most importantly, the reflex reduces the damage to hearing.