Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 13/11/2007 14:55:53
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I’ve heard that tools like hammers that make short, loud noises are supposed to be more damaging to hearing than something that makes a more continuous noise. I’d just like to get some confirmation on that.
<i>Asked by Jim Vandiver, Virginia</i>
Read this Question from our Podcast (http://www.thenakedscientists.com/HTML/content/questions/question/1791/)
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The Answer given in the program:
Whenever you listen to sound, the sound actually hits the eardrum. That sound is actually amplified by a series of tiny little bones in the ear called ossicles. These ossicles vibrate and stimulate the float within the cochlear which, in turn converts the sound energy into electrical energy which is perceived
as noise by the brain.
There are two different types of noise induced hearing loss. You have acute stage hearing loss, for example due to a large explosion or you may have something more gradual. This is more common in most people. This gradual increase in hearing loss is a combination of both the intensity of the sound as well as the duration of the sound. So for example, someone who shoots guns for a hobby may be exposed to very short bursts of noise but very high intensity and they may experience a similar degree of hearing loss compared to someone who's in a slightly different environment where the sound intensity's actually much lower but much more constant (e.g. the mining industry). There are also additional factors that can influence noise induced hearing loss. It's not just the combination of noise because people's tolerance to noise varies. Therefore there's some genetic influences in this as well. Noise induced hearing loss is not just the simple of noise experienced but also the genes that influence your hearing.
Yujay, ENT registrar at Addenbrooke's Hospital
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I've heard that tools like hammers that make short, loud noises are supposed to be more damaging to hearing than something that makes a more continuous noise. I'd just like to get some confirmation on that.
Well, it's going to depend also on the relative loudness of the sounds, and I'm not exactly sure how you define the loudness of very short sounds.
Hearing damage is also reckoned to be a function of both sound level and duration of exposure (for the same loud sound, days worse than hours worse than minutes, for example).
However... the ear has an interesting little muscle on one of the little bones (the malleus, I think) connecting to the eardrum which can act to reduce the amount of sound-energy transferred to the cochlea when the sound gets too loud. This muscle operates when the sound gets too loud... but takes a few (tens of?) milliseconds to respond. Consequently short-sharp sounds can do more damage than you might otherwise expect compared to more continuous sounds.
I've no idea how long it takes for the muscle to release and restore the normal sensitivity again after the loud sound has passed.
Take care of your ears folks; in mammals the little hair cells in the ear don't repair themselves when damaged, and living with a hearing problem is a misery. [:(]
When the inner hair cells get damaged you can lose all sensitivity to certain frequencies (cochlea dead regions), and no amount of amplification can bring them back.
I'm 32 and have a Dead Region in my left ear (no idea why, I've evidently had it since I was very young), and I cannot perceive pure tones with frequencies between about 2.8kHz and 5-6kHz with that ear. When a tone of that frequency is really turned up loud enough I perceive an "ethereal" sound which has a vague lower-frequency component and a much higher screechy-squeaky component (presumably detected by the nearest functioning hair-cells which are centred on very different frequencies). It doesn't have a proper pitch, and doesn't sound anything like a "proper" tone of that frequency as heard in my right ear.
Nice animation of the cochlea at http://147.162.36.50/cochlea/cochleapages/overview/history.htm
Various other illustrations and microscope images at http://147.162.36.50/cochlea/ (but the site isn't easy to navigate)
The Anatomy section has some of the clearest drawings of the cochlea I've found yet.
There's a cool video of a dancing hair-cell at http://ccrma.stanford.edu/courses/220a-fall-2001/lectureNov2.html
The ear is fascinating - especially all the signal-processing that happens in the cochlea.
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It's many years since i undertook my health and safety training, so this may be way off the mark.
To begin with, hearing and hearing loss is individual, to some extent. One person may be able to tolerate a higher sound than another without any permanent damage to the hearing.
I think that generally sounds beloe 85db are too weak to cause damage, those above 85db and below 140db do cause damage but not (generally) immediate, this is a gradual process over a working day for many years. Sounds above 140db can certainly cause immediate hearing loss.
Then you have to factor in things such as age and even sex, also distance from the sound. Take for example a firework, although they are generally around 100db so should not cause immediate damage, if you were too close at the time it "banged" it could cause immediate damage.
so i guess that whether it's a hammer or a chainsaw, depends on the relative db of the noise, age, and exposure time.
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To begin with, hearing and hearing loss is individual, to some extent. One person may be able to tolerate a higher sound than another without any permanent damage to the hearing.
I think my recent reading implies that yes, some people are more susceptable to noise-induced hearing losss than others. It may be partly genetic, but several papers seem to indicate that the antioxidant vitamins (A,C,E, etc) may also provide some immunity to loud-noise damage (or facilitate rapid repair before the damage becomes permanent).
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I think my recent reading implies that yes, some people are more susceptable to noise-induced hearing losss than others. It may be partly genetic, but several papers seem to indicate that the antioxidant vitamins (A,C,E, etc) may also provide some immunity to loud-noise damage (or facilitate rapid repair before the damage becomes permanent).
I did hear that people of darker skin have better hearing, i can't remember how that works though.
Back to the question.
tools like hammers that make short, loud noises are supposed to be more damaging to hearing than something that makes a more continuous noise
If i am right about a firework being around 100db, and that being too close can cause immediate and permanent damage, then if you then think that an ipod can give you a continuous 100db without causing immediate and permanent damage. Then i would have to say that the answer to the question is Yes, a short loud noise is more damaging than one that makes a continuous noise, but only over the short term.
The risk of hearing damage increases in relation to the level, duration, and distance you are to the noise.
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If i am right about a firework being around 100db, and that being too close can cause immediate and permanent damage, then if you then think that an ipod can give you a continuous 100db without causing immediate and permanent damage. ...
Also the ear is most sensitive to noise-induced loss at around 3-5kHz (I think I read that the loss occurs at about half an octave higher frequency than the noise exposure). These mid-high frequencies are those that the ear is most sensitive to on an absolute scale (in terms of air vibration amplitude), owing to them being near a natural resonance of the ear. Depending on your firework, I'd guess that the frequency spectrum is concentrated towards the less-harmful lower frequencies than a hammer or pneumatic drill which has strong mid-high frequency content.
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There is more to the problem than pure decibels. I noticed that it is important if you are mentally prepared for the noise. If you hammer yourself you know exactly when the noise is going to occur. So it can be more disturbing (harmful?) for the person standing next to a blacksmith than for the blacksmith himself. Playing in the opera orchestra I noticed that how you react on noise (volumepeaks in the music) depends on different factors like your attitude to the noise (love it/ hate it), if you know when noise is going to happen, if you are tired, unwell etc. When playing in the operapit soundlevels sometimes exceed healthy levels, but the most disturbing thing is a sudden unprepared noise, even if it is not that loud. So I would guess that the hammer is more dangerous than the chainsaw.
Mikael Crafoord, Stockholm
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There are three factors to hearing damage that others have mentioned: intensity, duration, and frequency. In general, high intensity sounds can be safe (not causing permanent hearing loss) when only exposed to in short durations (such as a hammer strike). However, even relatively "soft" sounds can produce permanent hearing loss if the exposure time is much longer. Finally, higher frequency sounds are more damaging to the ears than lower frequency sounds of the same energy (dB). Here's some info from the occupational safety and health association in the states:
TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1)
______________________________________________________________
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Duration per day, hours | Sound level dBA slow response
____________________________|_________________________________
|
8...........................| 90
6...........................| 92
4...........................| 95
3...........................| 97
2...........................| 100
1 1/2 ......................| 102
1...........................| 105
1/2 ........................| 110
1/4 or less................| 115
____________________________|________________________________
Footnote(1) When the daily noise exposure is composed of two or
more periods of noise exposure of different levels, their combined
effect should be considered, rather than the individual effect of
each. If the sum of the following fractions: C(1)/T(1) + C(2)/T(2)
C(n)/T(n) exceeds unity, then, the mixed exposure should be
considered to exceed the limit value. Cn indicates the total time of
exposure at a specified noise level, and Tn indicates the total time
of exposure permitted at that level. Exposure to impulsive or impact
noise should not exceed 140 dB peak sound pressure level.
from http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735
A couple notes: the dBA scale is a high-frequency weighted scale that more effectively captures dangerous sound levels. The footnote mentions that impact noise should not exceed 140dB. To get an idea of HOW loud this is, if you're using a hammer on a nail, you're not likely to be exposed to sound levels more than about 110dB. If you put your ear right up to it, you can probably get up to 130-150dB. Hitting a hammer on a steel beam will probably be around 120-140dB, while producing a higher frequency sound than the nail in wood. The "threshold of pain" is a useful measure of dangerous sounds. When you feel a sharp pain in your ears after hearing a very loud sound, you can be fairly sure that you've heard a sound of 120-140dB or louder. This is an indicator that you do not want to expose yourself to continued sound at that level.
I can't attest to the accuracy of this site, but it has some other useful examples of various sound levels: http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm
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I'm not sure if this is true or works but.
A friend who lived during the Blitz said that they were told to keep their mouths open when the bombs were going off. It was meant to help equalise the sound pressure.
As a comment. The common use of headphones over long periods, especially the "in-ear" types, I'm sure must be bad for the hearing. I'd love to know how much db's they can output.
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In-ear earphones are often turned up very loud to compensate for the absence of vibrations which the rest of the body feels with loud, live, music performances. I am waiting for someone to produce a 'sound jacket' for producing the full concert experience for the listener. It would be less intrusive than the damned sub woofers in lads' cars and they could continue to listen when not in their vehicle. Battery life could be a problem. . . . .
I have tested (on a very casual basis) the loudness level which many kids use for their earphones. Higher than 90dB is not uncommon yet they smile when I say that sustained listening at that level will surely cause damage. You can't tell em.
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Everyone talkes about decebels and we do know that loud sounds can damage the hearing. But the biggest factor in todays world that is affecting damaging peoples hearing ( and this did not exsist yars ago )is the high frequencies that are produced from computer hard drives( not the fan noise) but the ultra high pitched frequencies that are produced from a disk spinning at 7000 rpm + This bombards the microscopic hairs in the ear with constant sound waves that we humans were never meant to deal with. Think about it. Nothing in nature produces damaging frequencies like this. Of coarse a dolphin and a bat only use high FR to locate but I donm't think there going to blast you with a killer sound wave. YES, computer hard drives as well as things that produce EMFs can cause stress and hearing damage.
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Nothing in nature produces damaging frequencies like this. Of coarse a dolphin and a bat only use high FR to locate but I donm't think there going to blast you with a killer sound wave. YES, computer hard drives as well as things that produce EMFs can cause stress and hearing damage.- one word about you MORON
http://www.sciencedirect.com/science/article/pii/S0263224105001132
http://www.silentpcreview.com/SPCR_HDD_Testing
EMFs can cause stress and hearing damage- this only cause brain damage only in you...