Thanks Walt!
Klas.
At 13:13 2002-09-26 -0400, you wrote:
>Klas Strandberg wrote:
>> I have a question from a client about parabols and underwater recording. I
>> have no experience or understanding of it. Is there any clue out there?
>
>I looked into this a while back, and it seems there is little value with
>parabolas made out of most plastic materials. The problem being twofold,
>often the sound transmission characteristic of the parabola material is
>not much different from water and it fails to reflect but the sound goes
>right through it. The second has to do with the relative
>uncompressability of water, with several places seeming to state that
>the parabola will provide no gain or directionality. While others seem
>to be trying it:
>
>I did run across this, which is about a talk on the subject, maybe you
>can track it down.
>http://www.auditory.org/asamtgs/asa92nwo/4aEA/4aEA13.html
>
>Even so, I've been meaning to give it a try.
>
>Sound in water reflects very well off a air/water interface, so one
>parabola which should definitely reflect is to take two reflectors and
>seal a thin airspace between them. You would have to do pressure
>compensation if going very deep.
>
>Be aware that the surface of the water is a big reflector, and causes
>phase effects in shallow water. I've had occasion, using my hydrophone
>in very shallow ponds where I knew there were frogs making sound but I
>could not pick them up from a little ways away.
>
>The speed of sound in water is different than air, which will change the
>size of reflector needed.
>
>Let me know if you find out anything.
>
>Walt
>
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