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Tom Shaw
science forum beginner
Joined: 05 Jan 2006
Posts: 3
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 Posted: Thu Jan 05, 2006 9:48 pm Post subject:
Re: how your ears work
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According to my calcs if you lose one Hz a day and can hear 20,000 Hz to
start you will be about 53 and not be able to hear anything at all. Hmmmmm.
TS
"Didier A. Depireux" <didier@umd.edu> wrote in message
news:dpjm1l$q21$1@grapevine.wam.umd.edu...
| Quote: | In alt.sci.physics.acoustics J Ketutsalo <ei.kiitos@spammia.fi> wrote:
Angelo Campanella wrote:
Which brings up another (old) subject; the mechanism of hearing
damage via loud noises (NIPTS), especially why nerve damage damage
always starts in the 4k-6k region regardless of the spectrum of the
incoming noise.
Because at around 4k the transmission through the outer and middle ear
is most efficient, largely due to a quarter wavelength resonance of the
ear canal. At those frequencies you simply get more energy to the inner
ear to do the damage.
You probably know the standard shape of the human audiogram, as shown in
http://swfsc.nmfs.noaa.gov/prd/dsweb/tm-256/fig2.gif
At -5dB (the average threhold of hearing of a 17yo male at 4kHz) for a
passive cochlea, the corresponding vibrations of the fluid in your ear
correspond to rms displacement that are less than the mean displacement
from
Brownian motion. In other words, if it were not for active amplification
from outer hair cells, you would not hear anything. The counterpart is
that
it doesn't take much to mess up your threholds at 4kHz, unlike say at
200Hz
where it takes a lot of energy to get any activation in the cochlea.
OTOH, your high frequency hearing might be the first to go (we loose about
1Hz/day for the highest frequency we can hear) because all vibrations in
the
endolymph have to "pass by" the high frequency region of cochlea. So if
you
hear a very loud, low frequency, sound, it causes large oscillations in
the
endolymph that have to travel from the base of the cochlea (high-frequency
region) to the apex (low-frequency). The shearing effect of this traveling
wave might cause damage to the whole cochlea, even the parts that are not
tuned to low frequencies. Combine that with high sensitivity to 4-7kHz...
Didier
--
Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (lab)
University of Maryland -1273 (off)
Baltimore MD 21201 USA Fax: 1-410-706-2512 |
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Didier A. Depireux
science forum beginner
Joined: 13 Sep 2005
Posts: 7
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| Posted: Fri Jan 06, 2006 1:21 am Post subject:
Re: how your ears work
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In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote:
| Quote: | According to my calcs if you lose one Hz a day and can hear 20,000 Hz to
start you will be about 53 and not be able to hear anything at all. Hmmmmm.
|
Okay, so let me be more precise. You start loosing your upper-frequency of
hearing at around 15 years of age (actually, the highest audible frequency
for young kids has never been measured reliably. When someone did it on me
when I was about 10, my highest audible frequency was around 22500Hz for
about 100dB SPL), and as far as I know, your hearing loss slows down around
age 50.
I mostly had to make the point that you loose your high frequency hearing
reliably, whereas the lowest audible frequency does not change that much.
Didier
--
Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (lab)
University of Maryland -1273 (off)
Baltimore MD 21201 USA Fax: 1-410-706-2512 |
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Tom Shaw
science forum beginner
Joined: 05 Jan 2006
Posts: 3
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| Posted: Fri Jan 06, 2006 9:31 pm Post subject:
Re: how your ears work (OT)
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I'm sorry. I was just teasing you a little. I am glad to find out that my
hearing loss slows down around 50 but it apparently does not stop. I am now
at the point where I am bothered by extraneous noise while trying to listen
to conversation and that seems to be getting worse. This seems less a
problem with frequency response as it is a problem with noise rejection at
the mental level.
Fortunately I dont notice losing highs any more but probably am.
FWIW I bucked rivets in the manufacture of B-24 center-wings when I was
eighteen for a few months. That requires you to be inside the wing while
the rivet gunner is outside. Sort of like being inside an oil drum with
somebody pounding a hammer on the outside. In those days, WWII, nobody
worried about ear protection.
Today you are not allowed in the airframe factory without ear protection.
LOL. In any case my high frequency hearing is shot and that experience was
surely part of it's cause.
TS
PS Skeet shooting isn't such a hot idea for musicians either.
| Quote: | A. Depireux" <didier@umd.edu> wrote in message
news:dpk7em$4gg$1@grapevine.wam.umd.edu...
In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote:
According to my calcs if you lose one Hz a day and can hear 20,000 Hz to
start you will be about 53 and not be able to hear anything at all.
Hmmmmm.
Okay, so let me be more precise. You start loosing your upper-frequency of
hearing at around 15 years of age (actually, the highest audible frequency
for young kids has never been measured reliably. When someone did it on me
when I was about 10, my highest audible frequency was around 22500Hz for
about 100dB SPL), and as far as I know, your hearing loss slows down
around
age 50.
I mostly had to make the point that you loose your high frequency hearing
reliably, whereas the lowest audible frequency does not change that much.
Didier
--
Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (lab)
University of Maryland -1273 (off)
Baltimore MD 21201 USA Fax: 1-410-706-2512 |
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Angelo Campanella
science forum Guru Wannabe
Joined: 08 May 2005
Posts: 226
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| Posted: Sat Jan 07, 2006 12:36 am Post subject:
Re: how your ears work
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Didier A. Depireux wrote:
| Quote: | In alt.sci.physics.acoustics J Ketutsalo <ei.kiitos@spammia.fi> wrote:
Angelo Campanella wrote:
Which brings up another (old) subject; the mechanism of hearing
damage via loud noises (NIPTS), especially why nerve damage damage
always starts in the 4k-6k region regardless of the spectrum of the
incoming noise.
Because at around 4k the transmission through the outer and middle ear
is most efficient, largely due to a quarter wavelength resonance of the
ear canal. At those frequencies you simply get more energy to the inner
ear to do the damage.
You probably know the standard shape of the human audiogram, as shown
in http://swfsc.nmfs.noaa.gov/prd/dsweb/tm-256/fig2.gif
|
OK. The resonance explains that at 4 kHz we have the best threshold. I
actually enjoyed that for a while in grad school where I used a "Benham
Wave Analyzer" (a heterodyning ultrasound receiver) to tune and measure
various faint ultrasounds. Mr. Benham was a blind electrical engineer.
His instrument used a BFO to create a heterodyne at 4 kHz which was
tuned in, then nulled by hand with the aid of a calibrated attenuator.
Anyway, I thought it neat then that he used 4 kHz (he being blind and
having pristine hearing).
| Quote: | At -5dB (the average threhold of hearing of a 17yo male at 4kHz) for a
passive cochlea, the corresponding vibrations of the fluid in your ear
correspond to rms displacement that are less than the mean displacement from
Brownian motion. In other words, if it were not for active amplification
from outer hair cells, you would not hear anything. The counterpart is that
it doesn't take much to mess up your threholds at 4kHz, unlike say at 200Hz
where it takes a lot of energy to get any activation in the cochlea.
|
OK. Point made. Pristine hearing is also frail in that regard.
| Quote: | OTOH, your high frequency hearing might be the first to go (we loose about
1Hz/day for the highest frequency we can hear)
|
OK. An oversimplified model of presbycusis...
| Quote: | because all vibrations in the
endolymph have to "pass by" the high frequency region of cochlea.
|
That's dwells on the point I am driving at. The "Cause and Effect"
phenomenon here ("Epidemiology?"), according to your expressed model is
that it's a happenstance of the location of hair cells. Any hair cell in
that high liquid acoustic velocity corridor is going to be zapped. If
that is the case, then a bit more publicity and proof-of-prinicipal work
and publishing of same is in order, IMHO.
| Quote: | So if you
hear a very loud, low frequency, sound, it causes large oscillations in the
endolymph that have to travel from the base of the cochlea (high-frequency
region) to the apex (low-frequency). The shearing effect of this traveling
wave might cause damage to the whole cochlea, even the parts that are not
tuned to low frequencies. Combine that with high sensitivity to 4-7kHz...
|
OK all of that follows from that model. Some additional parameters,
then, presuming that liquid velocity and shear by hair cells is the
damage mechanism:
1- It seems clear that the relative motion of the liquid vis a vis hair
staffs is vital to hearing; that the Darwin effect (survival of the
fittest) will breed organisms whose cochlea promote high velocities from
faint sounds.
2- The shell structure of said evolved cochlea will have slightly
flexible walls since they will allow extraordinary inner chamber
velocities especially when a corridor is formed by a demising wall, i.e.
the spiral format.
3- Because the fluid should or must be contained, there will be a "base"
where the fluid velocity relative to the walls and surfaces carrying
hair cells must of necessity diminish to zero.
4- Because of the conical cross section of the spiral corridor, the
greatest relative velocity will occur most of the way from the apex
toward the base, perhaps at the 3/4 length location. Whatever hair cells
that reside there will experience the first damage when loud sounds as
received by the outer ear, and purveyed to the oval window by the middle
ear no matter the audio frequency of hat sound.
5- The assignment of specific audio frequencies to hair cells at
specific locations remains a mystery. But recent localization tests
indicate that precise localization includes the discriminating of time
differences in the microsecond range. Sound in water travels .005 feet
in one microsecond (1/20th of an inch), so hair cell positional
certainty is important to that end. The physiology of the sound path
including the stapes bone makes it imperative that asymmetries between
left and right ears shall be minimal to nil. A shortened trip to the
appropriate hair cells in the cochlear fluid will help.
6- Therefore, the need for precise left-right localization to avoid
threats, find food, and hence survive, probably resulted in the high
frequency hearing task being assigned by nature (nerve assignment to
specific hair cells) to be in the early part of the cochlear corridor
for those (high) frequencies vital to precision localization.
Angelo Campanella |
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Tom Shaw
science forum beginner
Joined: 05 Jan 2006
Posts: 3
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| Posted: Wed Jan 18, 2006 7:21 pm Post subject:
Re: how your ears work (OT)
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Thanks for your comments. I am not bothered by tinnitus. However my noise
discrimination is getting worse in that, at first, female voices on TV were
often unintelligible but I now notice some of the men's voices are also hard
to make out. And, by the way, it is a strong function of enunciation.
First rate actors are much easier to make out than a lot of the newbies on
the screen.
TS
"Didier A. Depireux" <didier@umd.edu> wrote in message
news:dqlu2f$rq9$1@grapevine.wam.umd.edu...
| Quote: | In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote:
I am now
at the point where I am bothered by extraneous noise while trying to
listen
to conversation and that seems to be getting worse. This seems less a
problem with frequency response as it is a problem with noise rejection
at
the mental level.
Fortunately I dont notice losing highs any more but probably am.
Sorry, I don't check news often any more, I don't know of a good service
to
do it, and the account I am using right now will disappear in a month.
With your work experience you probably also get tinnitus?
High frequency hearing is important in noisy situations. Think about it:
how
can you tell the difference between finger snapping in front of you and
behind you? In both cases the sound arrives at both ears at the same time.
A
good part of front-back localization of sounds has to do with the shape of
your pinna/ear: the ridges and convolutions are such that some frequencies
don't get transmitted that well to your eardrum (there's filtering from
your
pinna in other words); that filtering is very direction dependent. Hence
for
a familiar, broad-band sound, localization occurs in part thanks to your
ability to identify spectral notches in the perceived sound. Now if you
think about the size of your ear and the fact that sound travels at 1ft/s,
you will realize that the spectral notches will be in the 8kHz and up
region
of hearing. In a noisy environment, where you use all the cues you can
get,
parts of being able to follow a conversation depend on your ability to
stream or select the different sound sources that are present and focus
your
attention on one of those sources. If you have lost your high frequency
hearing, the pinna filtering is partially or mostly gone and that's one
less
cue you can use to isolate a sound source. Noise rejection is not just
"mental" as you say, it's also partially physical.
Didier
--
Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (lab)
University of Maryland -1273 (off)
Baltimore MD 21201 USA Fax: 1-410-706-2512 |
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Didier A. Depireux
science forum beginner
Joined: 13 Sep 2005
Posts: 7
|
| Posted: Wed Jan 18, 2006 7:53 pm Post subject:
Re: how your ears work (OT)
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In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote:
| Quote: | I am now
at the point where I am bothered by extraneous noise while trying to listen
to conversation and that seems to be getting worse. This seems less a
problem with frequency response as it is a problem with noise rejection at
the mental level.
Fortunately I dont notice losing highs any more but probably am.
|
Sorry, I don't check news often any more, I don't know of a good service to
do it, and the account I am using right now will disappear in a month.
With your work experience you probably also get tinnitus?
High frequency hearing is important in noisy situations. Think about it: how
can you tell the difference between finger snapping in front of you and
behind you? In both cases the sound arrives at both ears at the same time. A
good part of front-back localization of sounds has to do with the shape of
your pinna/ear: the ridges and convolutions are such that some frequencies
don't get transmitted that well to your eardrum (there's filtering from your
pinna in other words); that filtering is very direction dependent. Hence for
a familiar, broad-band sound, localization occurs in part thanks to your
ability to identify spectral notches in the perceived sound. Now if you
think about the size of your ear and the fact that sound travels at 1ft/s,
you will realize that the spectral notches will be in the 8kHz and up region
of hearing. In a noisy environment, where you use all the cues you can get,
parts of being able to follow a conversation depend on your ability to
stream or select the different sound sources that are present and focus your
attention on one of those sources. If you have lost your high frequency
hearing, the pinna filtering is partially or mostly gone and that's one less
cue you can use to isolate a sound source. Noise rejection is not just
"mental" as you say, it's also partially physical.
Didier
--
Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (lab)
University of Maryland -1273 (off)
Baltimore MD 21201 USA Fax: 1-410-706-2512 |
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Didier A. Depireux
science forum beginner
Joined: 13 Sep 2005
Posts: 7
|
| Posted: Mon Jan 23, 2006 8:18 am Post subject:
Re: how your ears work (OT)
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In alt.sci.physics.acoustics Tom Shaw <tshaw01@comcast.net> wrote:
| Quote: | discrimination is getting worse in that, at first, female voices on TV were
often unintelligible but I now notice some of the men's voices are also hard
to make out. And, by the way, it is a strong function of enunciation.
First rate actors are much easier to make out than a lot of the newbies on
the screen.
|
Stop watching TV! Seriously, when you utter a vowel, one of the
distinguishing features between the vowels /ah/ and /eh/, for instance, is
the location of the "formants", which are spectral peaks in the broad
spectrum generated by your vocal chords. For instance, I said "ahhhhhhh" in
a mike for 3 second, and took the Fourier transform of the result and put it
on
http://didier.theearlab.org/ahh.jpg
The discrete peaks are the harmonics due to the vibrations of my vocal
chords, and the continuous line is supposed to be the spectral envelope
(estimated by hand...). The position of the first 2 peaks, at around 500Hz
and 1500Hz, varies from vowel to vowel. The other 2 peaks vary a lot less.
It's a well known fact that when you enunciate, the peak to trough ratio of
formants (in the jpg above, the peak is at 600Hz and the trough at 1000Hz)
is maximal. Malcolm Slaney mentioned 15dB is typical. When you speak to
people familiar with your voice, esp with your family, it is often down in
the 4-5dB range (again, I got this number from Slaney).
The other factor to mention in response to your statement is that women have
a shorter vocal tract, which means that their formants are about 20% higher
in frequency, but their pitch is on average twice as high, which means they
have half as many harmonics or discrete lines in the jpg above, which makes
it harder to extract vowels from their speech (try to understand a soprano
singing an opera!).
BTW, it is a studied fact (look up Gordon-Salant on PubMed) that older
people have a harder time following fast speech, and it is not a result of
their audiogram showing hearing loss. I don't think this phenomenon has been
satisfactorily explained, but then again that's definitely nost my field!
Didier
--
Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
20 Penn Str - S218E http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (lab)
University of Maryland -1273 (off)
Baltimore MD 21201 USA Fax: 1-410-706-2512 |
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