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Author Topic: hearing damage, the same or different at different frequencies?  (Read 9615 times)

Weogo Reed

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hearing damage, the same or different at different frequencies?
« on: January 10, 2012, 11:04:32 pm »

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
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George Friedman-Jimenez

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Re: hearing damage, the same or different at different frequencies?
« Reply #1 on: January 11, 2012, 12:59:22 am »

I remember the thread but could not find it.

The best easily readable literature on hearing loss that I have read is the book "Hearing loss in musicians: Prevention and management" by Marshall Chasin, Plenum Publishing, 2009. It is simply written, comprehensive, up to date, medically accurate, well referenced, and answers most of the important questions for which answers currently exist.

To answer your question briefly, both Temporary Threshold Shift and Permanent Threshold Shift tend to occur approximately a half octave above the offending frequenc(ies). These refer to a shift upward in the loudness of sound necessary to reach the threshold that you can just barely hear it. Normal ears can just barely hear a sound at 0 dB, and if you can't hear it until it reaches 35 dB, for example, that is called a 35 dB threshold shift or 35 dB hearing loss. The shift in threshold can be temporary or permanent. The unprotected ear has a natural resonance in the 2700 - 3000 Hz range, due simply to the length of the outer ear canal. For this reason, much hearing damage tends to occur around this frequency and a half octave above it. This kind of noise-induced hearing loss often is seen on audiograms as a notch in hearing threshold in the 3000 Hz to 6000 Hz range, with relatively more normal hearing at lower and higher frequencies. The threshold graph is plotted with hearing threshold (hearing loss) increasing in the downward direction, vs frequency on the x axis, so a hearing loss around a given frequency looks like a notch. In violinists and piccolo players, the notch can extend up to 8000 Hz. The ear seems to be less susceptible to noise induced hearing loss at lower frequencies, as the great majority of people with NIHL have the greatest hearing loss in the 3k to 6k range.

The book gives good recommendations for prevention of hearing loss, including types of hearing protection to use, but the best recommendation in the book is to avoid mowing your lawn for at least 16-18 hours after a loud concert, to allow your ears to recover from the temporary hearing loss caused by the loud music. Friday and Saturday night gigs should have you covered until the weekdays come, when some of us with day gigs have too tight a schedule to be able to do the lawn after work.

The book is a bit expensive but much cheaper than even a single visit to the ENT doc, and only about 1% of the cost of set of hearing aids.
http://www.pluralpublishing.com/publication_hlim.htm

This free article by the same author has a little bit of the information in the book, but lacks the details: http://www.coordinatemovement.com/articles/HearingLossPreventionForMusicians.pdf

I have not yet read the more recent book by the same author, but it looks good and costs much less. http://www.harriscomm.com/index.php/b1170.html

The Sataloff book is written at a more technical medical level and has more details on hearing loss, but less on music, than the Chasin book:
http://www.crcnetbase.com/isbn/9780824753832

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Weogo Reed

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Re: hearing damage, the same or different at different frequencies?
« Reply #2 on: January 11, 2012, 02:30:50 pm »

Hi George,

Thanks for the reply, and I have some books to purchase!

The extra damage around 2700~3000Hz, and extending up to around 6000Hz, based on the focusing effect of the ear canal, makes sense.


Here's my original question stated slightly differently:

Is eight hours of 100db at 50Hz as damaging as eight hours of 100db at 500Hz?

Thanks and good health,  Weogo




I remember the thread but could not find it.

The best easily readable literature on hearing loss that I have read is the book "Hearing loss in musicians: Prevention and management" by Marshall Chasin, Plenum Publishing, 2009. It is simply written, comprehensive, up to date, medically accurate, well referenced, and answers most of the important questions for which answers currently exist.

To answer your question briefly, both Temporary Threshold Shift and Permanent Threshold Shift tend to occur approximately a half octave above the offending frequenc(ies). These refer to a shift upward in the loudness of sound necessary to reach the threshold that you can just barely hear it. Normal ears can just barely hear a sound at 0 dB, and if you can't hear it until it reaches 35 dB, for example, that is called a 35 dB threshold shift or 35 dB hearing loss. The shift in threshold can be temporary or permanent. The unprotected ear has a natural resonance in the 2700 - 3000 Hz range, due simply to the length of the outer ear canal. For this reason, much hearing damage tends to occur around this frequency and a half octave above it. This kind of noise-induced hearing loss often is seen on audiograms as a notch in hearing threshold in the 3000 Hz to 6000 Hz range, with relatively more normal hearing at lower and higher frequencies. The threshold graph is plotted with hearing threshold (hearing loss) increasing in the downward direction, vs frequency on the x axis, so a hearing loss around a given frequency looks like a notch. In violinists and piccolo players, the notch can extend up to 8000 Hz. The ear seems to be less susceptible to noise induced hearing loss at lower frequencies, as the great majority of people with NIHL have the greatest hearing loss in the 3k to 6k range.

The book gives good recommendations for prevention of hearing loss, including types of hearing protection to use, but the best recommendation in the book is to avoid mowing your lawn for at least 16-18 hours after a loud concert, to allow your ears to recover from the temporary hearing loss caused by the loud music. Friday and Saturday night gigs should have you covered until the weekdays come, when some of us with day gigs have too tight a schedule to be able to do the lawn after work.

The book is a bit expensive but much cheaper than even a single visit to the ENT doc, and only about 1% of the cost of set of hearing aids.
http://www.pluralpublishing.com/publication_hlim.htm

This free article by the same author has a little bit of the information in the book, but lacks the details: http://www.coordinatemovement.com/articles/HearingLossPreventionForMusicians.pdf

I have not yet read the more recent book by the same author, but it looks good and costs much less. http://www.harriscomm.com/index.php/b1170.html

The Sataloff book is written at a more technical medical level and has more details on hearing loss, but less on music, than the Chasin book:
http://www.crcnetbase.com/isbn/9780824753832
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Elliot Thompson

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Re: hearing damage, the same or different at different frequencies?
« Reply #3 on: January 11, 2012, 03:34:53 pm »

Hi George,

Thanks for the reply, and I have some books to purchase!

The extra damage around 2700~3000Hz, and extending up to around 6000Hz, based on the focusing effect of the ear canal, makes sense.


Here's my original question stated slightly differently:

Is eight hours of 100db at 50Hz as damaging as eight hours of 100db at 500Hz?

Thanks and good health,  Weogo


Hi.

Wouldnít the perception of oneís hearing contribute to what he or she finds irritating at high sound pressure levels in terms of frequencies?

There are only two frequencies that I find physically irritating under narrow Q conditions. The first one is 2.5 ( D Sharp 7 ) kHz and, the second is 17 kHz (C Sharp 10 ).
 

Best Regards,

Elliot.
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Jamin Lynch

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Re: hearing damage, the same or different at different frequencies?
« Reply #4 on: January 11, 2012, 03:42:55 pm »

I guess we are refering to live sound? In what type application would you have one without the other?
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Elliot Thompson

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Re: hearing damage, the same or different at different frequencies?
« Reply #5 on: January 11, 2012, 04:02:15 pm »

I guess we are refering to live sound? In what type application would you have one without the other?

It is more to wards those who are losing their hearing that boost the high frequencies excessively.

Best Regards,

Elliot.
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Dan Richardson

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Re: hearing damage, the same or different at different frequencies?
« Reply #6 on: January 11, 2012, 05:07:11 pm »

I guess we are refering to live sound? In what type application would you have one without the other?

Bluegrass on the one hand, dubstep on the other.
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George Friedman-Jimenez

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Re: hearing damage, the same or different at different frequencies?
« Reply #7 on: January 11, 2012, 05:17:56 pm »

The extra damage around 2700~3000Hz, and extending up to around 6000Hz, based on the focusing effect of the ear canal, makes sense.

Here's my original question stated slightly differently:
Is eight hours of 100db at 50Hz as damaging as eight hours of 100db at 500Hz?

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.
« Last Edit: January 11, 2012, 05:28:31 pm by George Friedman-Jimenez »
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Elliot Thompson

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Re: hearing damage, the same or different at different frequencies?
« Reply #8 on: January 11, 2012, 07:31:55 pm »


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.



Hello George.

I’ve discovered my dislike of 2.5 kHz ever since I was 13 so, I would imagine if this was indeed an early incarnation of hearing damage my hearing would not be able to detect 20 kHz at 31 much less be irritated by 17 kHz (17739.689 kHz ).


Due to how high frequency passes through air under various climates, I am more susceptible to such symptoms in the winter than the summer. I will definitely pay another visit to my doctor and ask her if she can recommend an audiologist.

Thank you for sharing your thoughts.

Best Regards,

Elliot.
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Stu McDoniel

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Re: hearing damage, the same or different at different frequencies?
« Reply #9 on: January 11, 2012, 08:57:56 pm »

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
I believe around 2k is where the ear is really really dam sensitive and yea 2.5khz is
annoying to every human on the planet.   That is the region the old paramectric grabs first thing
with me.   If you can make a narrow dip at that freq you really can change the annoyance factor of a soundsystem in a huge way. 
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Jon Lincoln

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Re: hearing damage, the same or different at different frequencies?
« Reply #10 on: January 12, 2012, 01:53:05 am »

Not sure if anyone here has related or noticed high spl frequencies 2k to 6k ish and alcohol don't mix. For years I have noticed frequency loud mixes causes more fights even at lower db levels, more than a louder clean balanced one. It also is the same with DJ's too. Of course distortion plays a factor also. Any thoughts?     
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Steve Blaski

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Re: hearing damage, the same or different at different frequencies?
« Reply #11 on: January 12, 2012, 01:58:58 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

Is this one of the links you were talking about? http://srforums.prosoundweb.com/index.php/m/95472/21640/

This one is also interesting: http://srforums.prosoundweb.com/index.php/mv/msg/48458/0/0/0/
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Marty McCann

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Re: hearing damage, the same or different at different frequencies?
« Reply #12 on: January 12, 2012, 03:21:41 pm »

[quote author=Elliot Thompson

Iíve discovered my dislike of 2.5 kHz ever since I was 13 so, I would imagine if this was indeed an early incarnation of hearing damage my hearing would not be able to detect 20 kHz at 31 much less be irritated by 17 kHz (17739.689 kHz ).


[/quote]

Hello Elliot,

I do not want to rain on your parade . . .  I seriously doubt that you can actually perceive a 20 kHz tone.

They used to test up to 10 kHz in hearing tests.  Now they only test up to 8 kHz.  I have a document from the University of Southern Mississippi that states that I am qualified to conduct an audio-metric hearing test.

Uh, and what oscillator or frequency counter did you use that has a 3 decimal place resolution? 

Don't burst a Scilla root cell in your Basilar Membrane now but can you hear this . . . . .  bullshit



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Dan Richardson

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Re: hearing damage, the same or different at different frequencies?
« Reply #13 on: January 12, 2012, 09:19:49 pm »

I seriously doubt that you can actually perceive a 20 kHz tone.

They used to test up to 10 kHz in hearing tests.  Now they only test up to 8 kHz.  I have a document from the University of Southern Mississippi that states that I am qualified to conduct an audio-metric hearing test.

If you can't hear above 8k, you're in the wrong business or at least reading the wrong forum.

The majority of audiologists are only testing for speech range intelligibility.

Many people can hear the flyback transformer on a tube TV, 15.734 kHz for NTSC and 15.625 for PAL.
I expect his irritant frequency is likewise a tone specifically generated by some piece of gear.


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Re: hearing damage, the same or different at different frequencies?
« Reply #14 on: January 12, 2012, 09:52:09 pm »

If you can't hear above 8k, you've been in the business too long.

Another possibility.........
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brian maddox

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Re: hearing damage, the same or different at different frequencies?
« Reply #15 on: January 12, 2012, 11:46:06 pm »

Many people can hear the flyback transformer on a tube TV, 15.734 kHz for NTSC and 15.625 for PAL.

yeah, that one i can hear loud and clear.  i was so happy when the vidiots went to lcd panels.  hooking up comm in video village when they were using all glass monitors was like putting a tiny ice pick through my head...
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Elliot Thompson

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Re: hearing damage, the same or different at different frequencies?
« Reply #16 on: January 13, 2012, 02:59:12 pm »

[quote author=Elliot Thompson

I’ve discovered my dislike of 2.5 kHz ever since I was 13 so, I would imagine if this was indeed an early incarnation of hearing damage my hearing would not be able to detect 20 kHz at 31 much less be irritated by 17 kHz (17739.689 kHz ).




Hello Elliot,

I do not want to rain on your parade . . .  I seriously doubt that you can actually perceive a 20 kHz tone.

They used to test up to 10 kHz in hearing tests.  Now they only test up to 8 kHz.  I have a document from the University of Southern Mississippi that states that I am qualified to conduct an audio-metric hearing test.

Uh, and what oscillator or frequency counter did you use that has a 3 decimal place resolution? 

Don't burst a Scilla root cell in your Basilar Membrane now but can you hear this . . . . .  bullshit

With the right amount of dB gain and a loudspeaker that can deliver ultra high frequencies I have no problem detecting anything ranging from 17 kHz to 20 kHz.

Around a year ago, I had a CD Player that offered a 19 kHz spike while idling all courtesy of the blinking LCD buttons. I’ve encountered a few fluorescent lights with ballasts that offered similar but not as piercing (possibly on the brink of dieing) when such a combination was popular.

There is nothing worse than hearing a very sharp high-pitched squeal that leaves a nauseating feeling throughout your body.

The Oscillator that offers a three decimal point is program I downloaded in 1998. It is called NCH Tone Generator. http://www.nch.com.au/tonegen/index.html

Best Regards,   
« Last Edit: January 13, 2012, 03:01:10 pm by Elliot Thompson »
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Chris Davis

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Re: hearing damage, the same or different at different frequencies?
« Reply #17 on: January 13, 2012, 04:18:36 pm »

With the right amount of dB gain and a loudspeaker that can deliver ultra high frequencies I have no problem detecting anything ranging from 17 kHz to 20 kHz.

Around a year ago, I had a CD Player that offered a 19 kHz spike while idling all courtesy of the blinking LCD buttons. Iíve encountered a few fluorescent lights with ballasts that offered similar but not as piercing (possibly on the brink of dieing) when such a combination was popular.

There is nothing worse than hearing a very sharp high-pitched squeal that leaves a nauseating feeling throughout your body.

The Oscillator that offers a three decimal point is program I downloaded in 1998. It is called NCH Tone Generator. http://www.nch.com.au/tonegen/index.html

Best Regards,   


+1 on the bit about hight pitched noise creating a nauseating feeling.   
I used to work in an area that had 20+ year old computer monitors that were on their way out, having been powered up 24/7 for their entire existence.  That was the source of the most noticeable effect I ever experienced. 
At first it took me a while to figure out where it was coming from.  I would be fine one minute, then the next I was felt like I was getting dizzy. My take on it is that over time I was confusing the sound of the old CRTs for the sensation of equilibrium being lost in my ears.   
I was getting tormented from old CRTs about 30 feet or more across the room.  Also I noticed they were often highly directional, move just a couple feet this way or that and it changes.  That is what made it difficult for me to pinpoint at first. (I thought maybe it might have been the overhead lighting)
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George Friedman-Jimenez

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Re: hearing damage, the same or different at different frequencies?
« Reply #18 on: January 13, 2012, 05:26:55 pm »

That is very interesting. Given the symptoms you describe, it is possible that that high pitched sound was actually at a high SPL. Has anyone here actually measured the SPL of that CRT noise?
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Dan Richardson

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Re: hearing damage, the same or different at different frequencies?
« Reply #19 on: January 13, 2012, 06:12:28 pm »

it is possible that that high pitched sound was actually at a high SPL. Has anyone here actually measured the SPL of that CRT noise?

It's extremely variable, unit by unit, case by case. Some CRTs are incredibly loud, others are not.
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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 Ė 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 itís 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 itís about 3dB down Öso 100 dB of 50Hz should have the same effect as 73 dB of 500Hz. Ö. personally I think thatís probably a bit too simpleÖ 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 Ė 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 itís 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 itís about 3dB down Öso 100 dB of 50Hz should have the same effect as 73 dB of 500Hz. Ö. personally I think thatís probably a bit too simpleÖ 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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