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David, While
this works perfectly in air there are several basic principles of acoustics
that encumber this methodology in the water: 1.
Impedance
mismatch - the transition of acoustical energy across the air/water interface
is very inefficient. This is demonstrated by the fact that you may not here a
distant vessel with your head out of the water but when immersed the vessel's
noise is very loud. Or as a kid, did you ever try to talk underwater to your
buddy; it came out garbled and weak. You would be better to pick a transducer
that is matched for water use…I don’t remember the numbers, but reception
efficiency goes way up. 2.
Speed
of sound in water – the speed of sound in the air is 343 m/s at 20°C and
1483 m/s in water at the same temperature. Since the speed is approximately
4.3 times faster in water, a much greater separation is required between the
transducers is necessary to determine the direction as you propose and many
more transducers to form a narrow listening beam. You still would not know
what side of the array (even with only 2 transducers as you propose) that the
sound was coming from. The trainable stereo transducers on old diesel boats were
about four feet (i.e. ~4.3 x the distance between our ears which are optimized for
determining sound direction in air). Late in the war, the arrays became much
larger. R/Jay Respectfully, Jay K.
Jeffries Andros
Is., Bahamas A
skimmer afloat is but a submarine, so poorly built it will not plunge. -----Original Message----- Joseph Perkel, I am lucky to have one of those jobs that allows a lot
of time to think...If you were to take two hydrophones, face them
forward in direction, seperate them with an air filled barrier also facing
forward, supply each a preamp, audio amp with adjustable sensativity controls
such as volume and gain, then provide each a small bar graph display, to
derive at the exact bearing of a detected contact, you would turn your boat
slowly passed the detected targets estimated location until the bar graph
displays are equal in activity and I would say within 5 to 10 degrees you
would know for sure as to its location. >From: "Joseph Perkel"
<joeperkel@hotmail.com> >Reply-To: personal_submersibles@psubs.org >To: personal_submersibles@psubs.org >Subject: RE: [PSUBS-MAILIST] Hydrophone systems >Date: Fri, 11 May 2007 11:57:43 +0000 > > > >David, > >Free is always the "right price"! I cannot
be there but, look forward to >seeing the results. > >Let me ask you this,... what can a homebuilder expect
in terms of narrowing >the bearings to prop sounds to say... within 5
deg? Is that a reasonable >expectation? > >Joe > > > > > > >From: "David Bartsch"
<dbartsch2236@hotmail.com> >Reply-To: personal_submersibles@psubs.org >To: personal_submersibles@psubs.org >Subject: RE: [PSUBS-MAILIST] Hydrophone
systems >Date: Thu, 10 May 2007 23:32:25 -0400 > >Joseph Perkel, > > Nice hydrophones...my plans are
free and will be available at the > >upcomming convention! > > > > > >>From: "Joseph Perkel"
<joeperkel@hotmail.com> > >>Reply-To: personal_submersibles@psubs.org > >>To: personal_submersibles@psubs.org > >>Subject: [PSUBS-MAILIST] Hydrophone systems > >>Date: Thu, 10 May 2007 18:44:20 +0000 > >> > >> > >>Peter and others, > >> > >>When I was considering a war-boat replica, I
had gone as far a > > >>acquiring plans for a homemade directional
hydrophone. >
>>http://www.digitalmarketingusa.com/hydrophone.html > >> > >>There are a number of commercial, albeit
expensive units that are > >>off the shelf such as >
>>http://www.sonotronics.com/html/products/receivers/mantrak.html > >> > >>The idea being that one could mount such a
device atop a short > >>shaft through a simple rotating thru hull.
One could have a fixed > >>compass rose on the inside with the bow
of course aligned > >>@ 360 deg, in order for the operator to
determine and call out > >>bearings. > >> > >>When I was diving, I was fairly certain
within.... I would guess a > >>90 deg swath of the direction of props to
try to keep myself from > >>being blended. This is >with human ears so I am quite sure these > >>units will get that down to the degree. > >> > >>If you really want to get fancy, there are
software programs > >>available that will determine range based
upon density and sound > >>wave propagation. This could be run on a
Panasonic "Toughbook". > >> > >>Joe > >> > >> > >> > >> >
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