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Author Topic: Noise Induce Hearing Loss (NIHL) : Is the correct decibel measure being used?  (Read 64 times)

RiderScan

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As a biker I’ve become aware of the inevitable hearing loss caused by the long term exposure to the wind noise in one’s helmet and I have started wearing ear plugs as a result.
Looking deeper into this, I discover that there are different ways of measuring the decibel value of sound levels and this is troubling because it doesn’t seem to reflect the actual measure of the sounds that cause hearing loss.
The standard measure used is the decibel value (dB). This is actually dB(A), ie: decibels using the “A weighting”.
The “A weighting”, which was developed in 1933, emphasises only those ‘pure’ tones that the human ear can detect, and de-emphasises those tones that the human ear cannot detect. It is a steep curve cutting off most frequencies below 500 Hz and above 6 kHz.
Apart from the fact that this research was only conducted on a small sample of people it was also done at “moderate” sound levels. At much higher volume levels it has been discovered that the response curve is much flatter. Ie: the human ear can pick up a much wider range of frequencies.
As a result of the “A weighting” the “standard” dB measure does not recognise “non-audible” tones nor loud sounds that may well cause hearing loss.
We KNOW from experience that hearing loss can also occur as a result of the non-audible noises, like the wind noise in your car window or in your helmet or the base speaker at a rock concert – which you can generally only feel in your body. The stats on hearing loss are still high and I wonder why we are still using outdated measures to manage this?
My feeling is that we need to lobby the authorities to examine this more carefully. Clearly hearing loss is still occurring at a large scale, and it is likely that one of the factors is that our measurement is wrong! We need some stats on the circumstances of people who have suffered hearing loss so we can get to the bottom of this and in the interim authorities should be lobbied to take a more conservative approach. Ie: to use the C weighting which is a much flatter curve, or even the Z weighting?
I believe that this is a very serious hidden issue and your advice would be appreciated.

alancalverd

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dB(A) weighting reflects the auditory sensitivity of the normal ear, and is therefore a useful measure of the auditory impact of wanted and unwanted sound. Most sound level meters are therefore provided with a A weighting for the assessment of signal clarity or noise nuisance.

However the primary transducer in a sound level meter is perfectly capable of a flat (Z) response and this should indeed be applied when measuring potentially harmful sound pressures. The problem is that for the most part, exposure to wind buffet (or even bass speakers - I am a bass player!) is voluntary and therefore not subject to legislation, hence "the authorities" are unlikely to take much interest. You can imagine the outcry if the Nanny State required you to drive with the windows shut, or ride your Hog with a helicopter ANR headset.       

CliffordK

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You didn't say what kind of a "biker" you are.  '

For a bicyclist, the most important safety issue is not getting smacked by a car, and I would discourage using ear plugs except perhaps in the most extreme conditions. 

Here in the USA, many motorcyclists get perfectly quiet motorcycles, and whack the mufflers off so they make a tremendous racket.  One person I talked to suggested that being heard helps them to be seen, however I certainly would worry about one's hearing with a loud motorcycle. 

I hadn't thought about wind noises in a helmet as it isn't an issue with my bicycle.  Perhaps there would be different sensations from different helmet designs such as a full face mask vs a skull cap helmet.  A number of manufactures make noise canceling headphones.  I wonder if a set could be optimized to the needs of motorcyclists and integrated into the helmets. 

As far as hearing damage, are you sure that noises outside of our audible frequency range actually are damaging?  Damaging to the same extent that audible sounds are?  Do you have research paper links?

evan_au

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hearing loss can also occur as a result of the non-audible noises, like the wind noise in your car window or in your helmet

"non-audible" is different from "non-noticeable".

As suggested in the OP, wind noise has a very wide spectrum, making it somewhat like "white noise". Some people use white noise to make other sounds less audible. But if you turn the white noise source on and off suddenly, you can certainly hear it - you just don't notice it.

This wide-band noise is certainly detectable on a noise level meter - whether on the A-weighted scale, or on the "flat" setting. But if people don't notice it, they could be subjecting themselves to excessive noise and resultant hearing loss without realising it.

I travel by jet on a regular basis, and I find that it does affect my hearing, so I also wear earplugs to shut out the wind noise and engine noise. On one occasion, I could only find one earplug in my bag - and this produced an odd sensation after the flight: one ear was noticeably less sensitive than the other. So I am sure that wind noise has both short-term and long-term impacts on your hearing.

Friends suggest that noise-cancelling headphones are good on jet flights, but I've not tried them. It's not clear if they reduce the noise by a few dB, only to replace it by music a few dB louder?

The cochlea contains frequency-selective hairs, and it has been found that after extremely loud sounds these hairs can shear off; after excessive continuous stimulation at much lower levels, the underlying nerve cells can effectively die of exhaustion.

Quote
Nanny State
France reportedly forced a big manufacturer to limit the maximum sound pressure level in their audio players, to avoid a pandemic of hearing loss amongst children and teenagers.
This was soon followed by software which removed said volume limitation, because some people like having their ears pounded.

See: http://en.wikipedia.org/wiki/Noise-induced_hearing_loss

RiderScan

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Hi Clifford
I didn't find specific research relating to NIHL in this area, although there must be some out there. I was wondering, with the arrays of skills on this forum, whether someone had some readily available research. I have seen some 'evidence' on the web but some of it may be 'anecdotal'. So any further info would be useful.
ps: The 'biker' bit was my motorcycle, although I am a cyclist too! :-)

 

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