Interesting questions about seashells

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Didier A. Depireux - 12 Feb 2004 15:50 GMT

I got the following question by mail:
My name is [...]. I am 10 years old and I am working on a project from
my science fair at school.

My original idea was going to be an invention: which was to see if I
could use the sea sounds coming from a shell as soothing white noise
for people to enjoy. I thought of this after my mom told me how she
could not sleep in NY City at nights because of the loud street sounds.
I thought it would be cool to use the sounds made by the sea shell to
block street sounds.

I found out thanks to your page
http://www.isr.umd.edu/~didier/seashell/index.html
that the sea shell is simply making some of the ambient sounds louder. There
is no sound as such to capture. It was interesting to know that no sound was
produced in a sound proof booth.

Now my question: With some loud noise in the background, do you think I
could still rig up my conch shell with a tiny microphone, with an
amplifier/mixer plus a speaker to extract any sea sounds for my project?

Didier

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Didier A Depireux ddepi001@umaryland.edu didier@isr.umd.edu
685 W.Baltimore Str http://neurobiology.umaryland.edu/depireux.htm
Anatomy and Neurobiology Phone: 410-706-1272 (off)
University of Maryland -1273 (lab)
Baltimore MD 21201 USA Fax: 1-410-706-2512

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Kari Pesonen - 12 Feb 2004 16:33 GMT

> I got the following question by mail:
> My name is [...]. I am 10 years old and I am working on a project from
[quoted text clipped - 18 lines]
>
> Didier

You can. I have measured/recorded different cavities to check the origin
of sea shell noise.
You may find literature from 1970's (and 1980's?) explaining that the reason
is so called physiological noise from the ear canal that reflects back to ear
from the sea shell (perhaps selectively amplified by the shell cavity/structure).
Then you measure the level inside or at the mouth of a cavity at different distances
from the ear, you notice that this explanation is not very valid, or at least
not the only one.

Kari Pesonen

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Didier A. Depireux - 12 Feb 2004 17:21 GMT

> You may find literature from 1970's (and 1980's?) explaining that the reason
> is so called physiological noise from the ear canal that reflects back to ear
> from the sea shell (perhaps selectively amplified by the shell cavity/structure).

Well, that explanation is not valid at all. When I go into my sound booth, I
hear no sea at all.

Didier

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Ban - 12 Feb 2004 17:30 GMT

>> You may find literature from 1970's (and 1980's?) explaining that
>> the reason is so called physiological noise from the ear canal that
[quoted text clipped - 5 lines]
>
> Didier

There will be feedback, if the microphone can catch some of the amplified
sound too. So the shell has to be in another room...

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ciao Ban
Bordighera, Italy

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The Ghost - 12 Feb 2004 21:15 GMT

snip....snip

> Now my question: With some loud noise in the background, do you think
> I could still rig up my conch shell with a tiny microphone, with an
> amplifier/mixer plus a speaker to extract any sea sounds for my
> project?

Yes, but you will still need to hold the shell up to your ear because the
gap between the shell and the ear provide the acoustic mass necessary for
the system to resonate and the real part of the acoustic input impedance of
the ear provides the acoustic resistance necessary to properly damp the
resonane. Also, in order to avoid acoustic feedback, you will need to have
the speaker in a different room. Fianlly, loud background noise will be
necessary. .

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Natural Science Forum / Physics / Acoustics / February 2004

Interesting questions about seashells