Anyone going to the AES (Audio Engineering Society) convention in L.A.
(Oct. 5 - 8)?=20
Anyone not want something checked out?
Scott Shepard
310-399-6515
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>From Tue Mar 8 18:22:45 2005
Message: 2
Date: Fri, 27 Sep 2002 17:10:14 +0200
From: Klas Strandberg <>
Subject: Re: Parabols and underwater?
Thanks Drew, I don't think it is very practical either, considering the siz=
e
and all.
I think someone should try a hydrophone at different distancies from an
underwater cliff. Near and far away from it. PZM?? That would give some
understanding.
Klas.
At 06:48 2002-09-27 -0400, you wrote:
>Klas,
>
>I also have no experience but purely speculating:
>
>There may be an interface problem as Walter correctly points out.
>But you should get a good reflection from a metal surface (ie Sonar
>detects subs well.)
>
>The speed of sound is much higher in water (1500 m/s vs 330 m/s).
>
>So the wavelength will be about 4 times longer for the same frequency.
>
>Therefore the diameter of the parabola must be significantly larger
>to capture the same range of frequencies.
>
>Good Luck, and let us know what you find out.
>
>Drew
>
>At 01:13 PM 9/26/2002 -0400, you wrote:
>>Klas Strandberg wrote:
>> > I have a question from a client about parabols and underwater recordin=
g. 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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