Re: [PSUBS-MAILIST] Piezo speaker...

[Phil Nuytten <72020.572@compuserve.com>]

Pat:
        Try Shure Bros. they have an extensive website . . their tabletop
microphone is a flat piezo element -  remember that all of these types of
transceivers need something to excite - to vibrate - By themselves, our
experience is that they are quite tinny and do not reproduce the mids and
lows well. You need the low end for range. Swimming pool speakers work OK -
they're just 8 ohm paper or plastic cone speakers in a brass housing . .
.expensive, tho'. Also the old tried and true Lubell hydrophones - see
www.lubell.com - they also, could be more than you want to spend . . You
might think about sawing a styrene or polyethylene  trawl float in half,
chuck in an 8 ohm stereo speaker, connect the wires to a couple of johnson
binding posts - or brass bolts, thru the plastic wall ( don't worry about a
dry connection - the wire to bolt path is the least resistance and current
leakage is minimal and will work fine on a temporary basis - but the wire
degrades over time - most commercial diver's comm systems used wet
connectors through the 60's and 70's) epoxy or cement the whole mess
together and away you go. You can get a cheap PA amp from radio shack to
power the speaker. Providing you have lots of bass ( low end) you can heard
this rig more than a mile away with 20 to 40 watts. Some of the original
whale song recording was done this way - using this rig as a mike.If you
plug this into the input of the amp in the sub and have a second small
speaker inside, you can use it as a hydrophone for listening or recording.
        We use a very elaborate system on Deepworker - analog to digital
convertors right at the transducer, along with DSP circuits, record to DAT
or harddrive and an inside DSP- D/A - amp to headset or speaker to monitor.
I have a good theoretical design for a 24 transducer/ 24 track digital
recorder - with the whole cetacean frequency range divided into 24 discrete
parts by filtering. Haven't built one yet, but when we do, I'd like to test
it in the Molokai Channel on the ancient whale-roads! Ahhh. . .so much
desire, so little time!
Phil Nuytten