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Author Topic: hearing damage, the same or different at different frequencies?  (Read 9588 times)

Weogo Reed

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Re: hearing damage, the same or different at different frequencies?
« Reply #20 on: January 13, 2012, 06:45:42 pm »

Hi Folks,

It appears this post has hit a (hearing?)nerve!

George,
Thanks for the clarification about ear focusing and resonance,
and all the other good information.

I do seem to remember some numbers about hearing damage at different frequencies, but can't put my finger on it just yet.

A friend noted that the EU sound level standards are more strict than in the US, and that since it is
EU governments who are footing the bill for hearing damage, it is in their best interests to keep costs down.
In the US, we almost expect to lose our hearing as we age...

Elliot,
At the moment I'm not focusing on irritating sounds, just sounds that are damaging to hearing.
Hearing politicians talk is often an irritating sound, even at low volume!!!

Jamin,
In particular I am looking at live sound, but other hearing damaging sources as well.

Jon,
I had forgotten about alcohol affecting hearing.  Smoking definitely affects hearing.

Steve,
Yes, thanks for finding those threads!

Some good info on UK hearing standards:
 http://www.cassafe.com/legislation/control-of-noise-at-work-regulations-2005.html

Interesting bit for folks who think their hearing will never be damaged:
 http://www.earbud.org/hearing_facts/virtual_hearing.html#

Thanks and good health,  Weogo



Weogo, regarding your first statement, it is not just focusing, the external ear canal is a tube about an inch (2.5 cm) long that actually has a resonant frequency somewhere in the 2700 - 3500 Hz range for most people. You can calculate the resonant frequency as f = c/4L where c is the speed of sound in air = 34,000 cm/sec and L is the length of the tube, approximately 2.5 cm for some people. So for those numbers, f=34,000/(4*2.5) = 3,400 Hz. The geometry is not a simple cylindrical tube, there are harmonics involved as well, and the width of the resonant frequency range is broader than a single frequency spike, but a gain of approx 15 dB has been measured for the resonant frequency of a human external auditory canal, compared with frequencies below 400 Hz and above 9000 Hz. You can think of the ear canal as a natural acoustic bandpass amplifier with a center frequency around 3000 Hz and a gain of around 15 dB.

Elliot, I would think the lower frequency, 2,500 Hz, that you find irritating probably represents the natural resonant frequency of your external auditory canal, and possibly some early hearing damage. People with damage to their hearing sometimes become more aware of certain frequencies at high SPLs, while still having an increased threshold of perception at those same frequencies. Or it could be purely perception. As I recommend for nearly all people in the music or sound business, I would suggest getting your hearing tested by an audiologist. At a very minimum, a baseline audiogram when beginning in this industry, then regular follow-up audiograms every few years, will help you identify hearing loss relatively early so you can take more aggressive preventive measures. In addition, audiograms in between the regular screening audiograms, when you perceive a problem with your hearing can be useful. These recommendations are probably too conservative, since evidence of hearing loss on an audiogram often indicates that permanent hearing damage has already occurred. For this reason, some audiologists recommend more sensitive screening tests like otoacoustic emissions testing, which can identify early effects of overexposure to loud sounds before permanent damage occurs.

Weogo, regarding your question, I don't think good research has been done to get frequency-specific estimates of risk of hearing damage from 50 Hz vs 500 Hz sound. Certainly you should never expose yourself for 8 hours a day to 100 dB SPL at either frequency without hearing protection.  Both 50 Hz and 500 Hz are far from the resonant frequency center, so the acoustic bandpass amplifier effect would not be significant in either case. Certainly, however, 100 dB at 500 Hz would sound much louder than 100 dB at 50 Hz, as shown in the equal loudness contours you cited. You would perceive your 100 dB SPL 500 Hz sound as 100 phons, but you perceive a 100 dB SPL 50 Hz sound as around 77 phons, according to that curve. As musicians and SR professionals, our natural reaction to this psychoacoustic effect is to crank up the bass until it sounds roughly as loud as the mids and highs (or even louder in some cases). So in real life with serious subwoofers and a real live DJ spinning and EQing the music, the actual dB SPL at 50 Hz would likely be EQed up to 100 phons to sound about as loud as the 100 phons at 500 Hz. This would be equivalent to a 50 Hz SPL of about 113 dB, to match the 500 Hz SPL of about 100 dB. We don't have enough research to tell us whether the 50 Hz 113 dB sound would be more likely to damage hearing than the 500 Hz 100 dB sound. The OSHA regulations and NIOSH recommendations and dB / time equivalencies sidestep this question by using A weighting and ignoring very low frequencies. They probably err on the side of not being protective enough, rather than being overprotective.

So my recommendation, which I follow religiously myself, is to bring hearing protection whenever you go into a place with music or sound over about 90 dBC for more than an hour. I actually bring an SPL meter to gigs, and have even been known to bring it to parties. You don't have to be that nerdy, you can learn to recognize sounds over about 90 dB without a meter. I have a very low threshold for putting my in ear hearing protectors in. The need to converse or to play music in tune and in time sometimes causes me to take them out even if the sound is too loud, but I usually keep them in most of the night.
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Peter Morris

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Re: hearing damage, the same or different at different frequencies?
« Reply #21 on: January 16, 2012, 07:36:02 am »

Hi All,

Please help with a subject that has been discussed here before...

Several years ago there was a significant thread about hearing damage, and whether low, mid and high frequencies at the same db level do the same amount of damage.

Can anybody point me to the thread(s), and or good literature on the subject?

I do know about the different perception of frequencies as show by Fletcher~Munson,
and the ISO 2003 hearing curve:
http://en.wikipedia.org/wiki/Equal-loudness_contour

Thanks and good health,  Weogo


dBA is the reference for measuring noise for hearing damage – the A curve therefore roughly approximates the problem areas.

 http://en.wikipedia.org/wiki/Weighting_filter

http://en.wikipedia.org/wiki/A-weighting

This link shows how you can calculate the effect of 50Hz  Vs 500Hz

http://personal.cityu.edu.hk/~bsapplec/single.htm

In general the OHS limit is 85 dBA for 8 hours. I think it’s based on a 5 day week (or something like that) resulting in a (??) percentage of the population experiencing hearing loss.

85 = 8 hours
88 = 4 hours
91 = 2 hours
etc.

The A curve at 50 Hz is about 30dB down, at 500Hz it’s about 3dB down …so 100 dB of 50Hz should have the same effect as 73 dB of 500Hz. …. personally I think that’s probably a bit too simple… but it gives some indication.   (see Geroge's comments)
« Last Edit: January 16, 2012, 10:30:26 am by Peter Morris »
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George Friedman-Jimenez

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Re: hearing damage, the same or different at different frequencies?
« Reply #22 on: January 16, 2012, 02:01:43 pm »

dBA is the reference for measuring noise for hearing damage – the A curve therefore roughly approximates the problem areas.

 http://en.wikipedia.org/wiki/Weighting_filter

http://en.wikipedia.org/wiki/A-weighting

This link shows how you can calculate the effect of 50Hz  Vs 500Hz

http://personal.cityu.edu.hk/~bsapplec/single.htm

In general the OHS limit is 85 dBA for 8 hours. I think it’s based on a 5 day week (or something like that) resulting in a (??) percentage of the population experiencing hearing loss.

85 = 8 hours
88 = 4 hours
91 = 2 hours
etc.

The A curve at 50 Hz is about 30dB down, at 500Hz it’s about 3dB down …so 100 dB of 50Hz should have the same effect as 73 dB of 500Hz. …. personally I think that’s probably a bit too simple… but it gives some indication.   (see Geroge's comments)
Not enough scientific research has been done to answer the question whether 100 dBSPL at 50 Hz has the equivalent potential to cause hearing damage as 100 dBSPL at 500 Hz. Comparing equivalent SPL levels using adjusted dBA, or dBC, or flat response dB measurements, or even the Fletcher-Munson curves or equal loudness contours will not answer the question. The small amount of research that has been done on this does suggest that given equivalent dBSPL, higher frequencies (especially in the 3-6kHz range) have more potential to do damage, hence the mandated and widespread use of dBA for regulatory purposes. It is not known whether the results of this research can be extrapolated down to the 50 Hz range. Doing that requires making strong assumptions without scientific support.

Making a more conservative (health protective)assumption that equal dBSPL will have similar potential to do damage at all frequencies implies that more damage will occur due to low frequencies, since typical popular music may overhype low frequencies to higher SPLs as I described in a previous post. Whether this is true or not remains to be studied, perhaps good scientific studies of the dubstep / hip hop / D&B / Reggae / Reggaeton generation's hearing loss as they get older will answer this question. Anecdotally, my wife and I reluctantly left a fundraiser Caribbean dance party on Saturday night because we could not tolerate the overly loud bass. No one could talk and my musicians' hearing protectors are less effective down at bass frequencies. The DJ would not turn down his subwoofers, which sounded at least 10-15 dB louder than his tops.
« Last Edit: January 16, 2012, 02:11:48 pm by George Friedman-Jimenez »
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