-----
Original Message -----
Sent: Saturday, May 12,
2007 5:29 AM
Subject: RE: [PSUBS-MAILIST]
Hydrophone systems
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-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of David Bartsch
Sent: Friday, May 11, 2007 10:28 PM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Hydrophone systems
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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