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Old 10th August 2010, 08:50 PM   #21
SY is offline SY  United States
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if there were nothing between you and the airport, 10 miles away, and if there were no other sounds, nothing for sound to reflect from
That's what makes it inverse square. They removed boundaries and reflections.
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Old 10th August 2010, 09:04 PM   #22
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Just for the record, note that sound pressure level (SPL) from a point source falls off with 1/r, not with 1/rČ. No inverse square law at work here...
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Old 10th August 2010, 09:20 PM   #23
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A long while ago I read (or saw on a TV show) about how quiet it can be in Antarctica on a still day. Whilst no where near the claims of the chalk experiment, the person was relating how they could hear the shutter click of their colleagues camera who was over 1Km away.

Just a random anecdote no more

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Old 10th August 2010, 09:21 PM   #24
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Just for the record, note that sound pressure level (SPL) from a point source
falls off with 1/r, not with 1/rČ. No inverse square law at work here...
Hi, No, that is a line source unless you think that does not drop off at all, /sreten.
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Old 10th August 2010, 09:31 PM   #25
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Just for the record, note that sound pressure level (SPL) from a point source falls off with 1/r, not with 1/rČ. No inverse square law at work here...
Thatwould be neat! How do you get the sound wave to be contained in a single point vector and not spread out as a sphere?
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Old 10th August 2010, 09:37 PM   #26
KSTR is offline KSTR  Germany
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Sound pressure - Wikipedia, the free encyclopedia
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Old 10th August 2010, 09:48 PM   #27
SY is offline SY  United States
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The square depends on if you mean pressure or intensity.

Let's look at pressure, since you like that one. Pressure drops by half for each doubling of distance. So the SPL would be 80 - 20log(1/16000) ~ -4dB ref 20uPa. And that's assuming loud chalk.
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Old 10th August 2010, 09:53 PM   #28
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And that's assuming loud chalk.
I was thinking that the chalk must have been made out of touch powder

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Old 10th August 2010, 09:59 PM   #29
KSTR is offline KSTR  Germany
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4dB lower than the established threshold of hearing, 0dB(SPL). Not too far out, I'd say. Bigger problem for a real chalk experiment might be HF absorbtion which is not modelled by the p~1/r relationship. Who's gonna take their subs down to Antarctica?

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Old 10th August 2010, 10:01 PM   #30
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There's that reference: 20 uPa.

The experiment is set up with nothing to reflect off of and no other sound... It's hard to know what the original speaker meant here, but perhaps he meant a theoretical reference of 0 uPa? Given the impracticality of the rest of it, who knows. The setup is clearly not in the realm of physically possible.

I'm not even sure what the implications of a zero background noise environment are. It's not really sensible to talk about, but perhaps it is mathematically possible? I don't know what the implications of changing the standard background reference are on Sy's SPL calculation.
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