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Physiology & Medicine / Noise Induce Hearing Loss (NIHL) : Is the correct decibel measure being used?
« on: 23/04/2014 18:59:10 »
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 The stats on hearing loss are still high and I wonder why we are still using outdated measures to manage this?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.
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.