General Question

girlfriday's avatar

At what decibel level can sound hurt your ears?

Asked by girlfriday (193 points ) July 2nd, 2007

and does it matter if it is a high- or low-pitched sound?

Observing members: 0 Composing members: 0

7 Answers

mabelrxu's avatar

[snip from wikipedia article on Sound]
Humans can generally hear sounds with frequencies between 20 Hz and 20 kHz (the audio range) although this range varies significantly with age, occupational hearing damage, and gender; the majority of people can no longer hear 20,000 Hz by the time they are teenagers, and progressively lose the ability to hear higher frequencies as they get older. Most human speech communication takes place between 200 and 8,000 Hz and the human ear is most sensitive to frequencies around 1000-3,500 Hz. Sound above the hearing range is known as ultrasound, and that below the hearing range as infrasound.

The amplitude of a sound wave is specified in terms of its pressure. The human ear can detect sounds with a very wide range of amplitudes and so a logarithmic decibel amplitude scale is used. The quietest sounds that humans can hear have an amplitude of approximately 20 ?Pa (micropascals) or a sound pressure level (SPL) of 0 dB re 20 ?Pa (often incorrectly abbreviated as 0 dB SPL). Prolonged exposure to a sound pressure level exceeding 85 dB can permanently damage the ear, resulting in tinnitus and hearing impairment. Sound levels in excess of 130 dB are more than the human ear can safely withstand and can result in serious pain and permanent damage. At very high amplitudes, sound waves exhibit nonlinear effects, including shock.
[end snip]

higher pitched sound has a higher frequency (shorter wavelength) ... so I guess the pressure would be applied "more times"? I have no idea ... but in real life, higher pitched sounds certainly sound louder / more painful / more annoying ... where as really bass tones just kinda reverberate within our ribcage ... or at least that's what if feels like to me ... hope this helps ^_^

bpeoples's avatar

OSHA has some good info here: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p;_id=9735

Note that the graph there is not "permissable sound" but a conversion from Octave-weighted to A-weighted measuring devices.

The chart in question is:
TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1)
______________________________________________________________
|
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

Which basically says 15 minutes @ 115dbA exceeds daily limits, while 8 hours @ 90dbA exceeds daily limits.

This is for continuous noise, "impact noise" is rated differently, and you can read all about it in the OSHA regs. They don't rate by frequency, only by hours/SPL (and there are some industrial noises that are only in certain octave bands).

mvgolden's avatar

When measuring sound levels for use in determining noise exposure levels we typically measure with an "A-weighting". The A-weighting decreases the contribution of lower frequency sound verses sound in the 1000 Hz to 3000 Hz range. It also decreases the contribution about about 3000Hz but not that much. As far as I know there has not been a lot of research done for the effect of noise below 20 Hz and above 20,000 Hz on hearing loss.

The OSHA limits above are a compromise. As you can see from the table above, OSHA says the for every increase in 5dB your time of allowable exposure drops in half. This is called the exchange rate. In reality every increase in sound by 3 dB is a doubling in sound energy. It seems to me that if the energy levels double your allowable exposure time should be cut in half to maintain the same noise dose. OSHA also allows you to be exposed to 90dBA for a 8 hour day. In my experience, that is quite loud.

I think the EU has a lower exchange rate and limits you to 85dBA in an 8 hour day, but don%u2019t quote me on that.

In practice, if you need to raise your voice so that someone standing at arms length distance can understand you, you should wear ear plugs. I bought a pair of musician ear plugs from a while ago. They are designed to block sound more evenly then standard earplugs so music does not sound as weird.

samkusnetz's avatar

another important thing to remember is that sound levels vary by distance. a common quote is "a jet plane taking off is 140 db spl" which is true at one distance away from the plane, somewhere between ten and fifty feet away i expect. but as you double the distance from the sound source, you subtract 6 db. so if a jet plane is 140 db at ten feet, then it's 134 db at twenty feet. and so on.

mabelrxu's avatar

again ... this is not proven or anything, but wouldn't it make more sense if the db level drops exponentially or at least not linearly? rarely much if anything in nature / reality is linear ... just a thought though ^^

mvgolden's avatar

It actually drops logarithmically. If you go back the definition of sound level SPL = 10 * log (Pressure/Ref. Pressure)^2.

Now sound observes spherical spreading. Meaning that the energy travels way from the source in ever growing sphere. If you work through some physics that I am too tiered to go through right now, you will find that the sound pressure drops off as 1/r, where r is the distance form the source.

So if you double the distance the pressure decreases in halve. Now go back change the Pressure in the SPL equation by 1/2.

SPL = 10 * log (1/2 * Pressure/ ref Pressure )^2
Becomes
SPL = 20 * log (1/2 * Pressure/ ref Pressure)
Becomes
SPL = 20* (-.3) 20 * log (Pressure/ref Pressure)
Becomes
SPL = 20 * log (Pressure/ref Pressure) - 6 dB

Granted it is late and I could have flubbed a sign in there somewhere, but that is by sound decreases by 6dB for every doubling of distance. While the SPL drops of logarithmically the Pressure does in fact drop of linearly.

thybigballs's avatar

actually sound amplitude doubles every 6dB and not the above mentioned 3dB. I use ultrasonics in my work for material evaluations and prove this everyday with my electronic equipment

Answer this question

Login

or

Join

to answer.

This question is in the General Section. Responses must be helpful and on-topic.

Your answer will be saved while you login or join.

Have a question? Ask Fluther!

What do you know more about?
or
Knowledge Networking @ Fluther