...This very interesting subject caused me to search for a text, I found an appropriate one but, I'm not quite in the market for it.
http://www.scitechpub.com/burdic.htm
Still, if I were building a war-boat, I think the $ 80 would be money well spent.
Joe
From: "Jay K. Jeffries" <bottomgun@mindspring.com>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] Hydrophone systems
Date: Sat, 12 May 2007 11:20:26 -0400
Peter,
I haven?t looked at the Dolphin Ear hydrophones (missed the URL link). If they are true hydrophones that are impedance matched to water, you might get some directionality by mounting one with a large air space behind it to negate the rear lobe. If you look closely at the old German Type IX40C subs, there is a semi-circle array of hydrophones around each of the bow planes. The array gave very good directionality and they were far enough back on the hull to use the hull as shielding to tell if the signal was coming from port are starboard. By changing course and thus re-pointing the array, the exact direction could be determined. They may have been able to electronically ?steer? the arrays directionality. Early US subs had a ?T? sticking up off of the deck, usually in the bow, and this was a trainable array.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
A skimmer afloat is but a submarine, so poorly built it will not plunge.
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Peter Madsen
Sent: Friday, May 11, 2007 10:40 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Hydrophone systems
Jay,
-and others of you fine people who knows things...!
Kraka is slim - exactly 1.0 meters hull diameter - thats is just less than four feet...and I have ordered two hydrophones of the Dolphin Ear type. These are really intended for any type of experinent - but my intention was to things:
Place a single hydrophone in front af of deflector - like a parabol - or place one hydrophone on each side of the hull, with a sterio type amplyfier and headsets...now - what do you think my chancer are to improve my acustic perception of the world around the sub compared to todays method - ysing my human ears inside tyhe subs pressure hull ?
What ever the results I will post them here for psubbers to use. Any ideas are welcome.
Regards,
Peter
----- Original Message -----
From: Jay K. Jeffries
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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