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Old 11th August 2010, 02:40 PM   #41
SY is offline SY  United States
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sreten, things cancel so the numbers work out the same. 10log(1/r2) is the same as 20log(1/r).
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Old 11th August 2010, 02:47 PM   #42
sreten is offline sreten  United Kingdom
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sreten, things cancel so the numbers work out the same. 10log(1/r2) is the same as 20log(1/r).
Hi Sy, True, but you cannot say there is not a 1/r2 principle at work, its not 1/r, /Sreten.

(the 1/r power and SPL principle applies to a line source. Pressure becomes the square root.)

Last edited by sreten; 11th August 2010 at 02:55 PM.
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Old 11th August 2010, 03:08 PM   #43
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SY, I think the whole angstrom claim stems from the fact that under the right conditions, it's possible to hear the thermal noise of the air itself as the air molecules randomly bang into the eardrum.

Assuming that's the case, the question then becomes, by what amount would those air molecules banging into the eardrum displace it?

se
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Old 11th August 2010, 04:19 PM   #44
sreten is offline sreten  United Kingdom
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Hi All,

Its not simply just a question of displacment, that is just a number, its energy,
or power, or SPL, displacement drastically reduces with frequency, for the
critical 3kHz to 4kHz band the ears shape itself will amplify the signal to
more than implied by the simple mathematics that apply lower down.

The numbers (I have not worked them out) probably represent an equivalent.
I guess your talking about the equivalent displacement @4kHz for ~ -10dB.
It may be a higher frequency with lower displacement but a higher dB level.

/Sreten.

Last edited by sreten; 11th August 2010 at 04:21 PM.
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Old 11th August 2010, 05:21 PM   #45
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If you look at the literature (I do NOT mean a wiki), the "one-molecule" estimate has been around since the 1970s.

A decade or two later, the estimate was refined and then conjectured that if the sensitivity was any better, you would be coming up against limits set by Brownian Motion
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Old 11th August 2010, 05:47 PM   #46
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It is not the dB that you divide for that, but the amplitude. If you calculate in dB you need to subtract the attenuation. 16000m give some 168db attenuation (just for inverse square law, no friction losses), so the final signal would be at -96dB. Air friction losses would drive that even lower.
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Old 11th August 2010, 06:42 PM   #47
jlsem is offline jlsem  United States
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As soon as you read that, you know you're dealing with garbage.

I'll leave the chalk calculation as an exercise for the reader. It is similarly garbage.
Yes. A reliable secondary source for that kind of data is Fundamentals of Acoustics by Lawrence Kinsler and Austin Frey, published by John Wiley & Sons. They state that the human ear can respond to sound pressures on the order of .0001 microbars, which corresponds to a displacement of the eardrum of .01 nm, which is roughly 1/10 the diameter of a hydrogen gas molecule, not 1/100.

The changes in pressure due to thermal agitation of gas molecules falls below this threshold, so despite extraordinary claims, this type of noise is inaudible.

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Over 35 years ago as an engineering student in the auto industry (with 20 year old ears) I took the opportunity to spend over an hour in a state of the art anechoic chamber in the dark just for the experience. Once your ears recover from the background noise that usually assaults them you hear two things very distinctly. The throbbing of your pulse and a whine seemingly at maybe 1kHz which is the nervous system background noise.
Interestingly enough, although the ability to hear higher frequencies fades with age, the ability to detect these miniscule changes in pressure and corresponding displacement of the eardrum in the range of 1kHz to 5kHz stays with us.

John

Last edited by jlsem; 11th August 2010 at 06:50 PM.
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Old 11th August 2010, 08:05 PM   #48
Cassiel is offline Cassiel  Libya
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When you think about it this thread has gone pear shaped. So all this calculations and headscratching because some nutty said you could hear a piece of chalk drop ten miles away from you. Ask a normal person and he will need five seconds to get that right. No way.

What difference does it make anyway? This has nothing to do with audio electronics concerning the human ear. Is it possible for audio engineers to build an electronic device that will have the same capabilities that the human ear has? No it isn't.
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Old 11th August 2010, 09:59 PM   #49
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I'd suggest you to stop reading threads like this
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When you think about it this thread has gone pear shaped.
I'd suggest you to stop reading threads like this.

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Old 11th August 2010, 11:03 PM   #50
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Is it possible for audio engineers to build an electronic device that will have the same capabilities that the human ear has? No it isn't.
considering that we have developed atomic force microscopes I consider that to be rather bold statement limiting a priori the capabilities of engineering.
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