Ken,
I asked a scientist at the Technical
University of Denmark who is a friend of mine to take a closer look at your
hydrophone - and I received my self #2 hydrophone.
During a test over the side of a boat It did
exactly the same as the first - ergo - no ( likely ) error in the amplifier
or hydrophone.
Then tonight - my scientist called me with his
conclusions:
Result 1: I know to little of how to use highly
sensitive instrumentation like this.
Result 2: Given instructions on how to install and
use the hydrophone - it turned out to be a very usefull sensor - especially
in combination with a submarine.
My friend concluded the DolphinEar is a
good and very sesitive hydrophone at its cost - yet
he recommended a better cable, or the amplifier to be build into the
hydrophone itself.
He explained that the cable must be
handled with extreme care not to produce noise, since it itself has a pieco
electric effect - hence makes noise when
mechanically stimulated.
He also explained that the polymer and
epoxy parts would not have unlimited life in a marine environment. This is not a
problem for the DolphinEars normal use
but when installed permanently submerged on
the sub it would become a problem over time.
Polymers simply are not impenetrable by water.
Tonight the first hydrophone was therefore
installed like this...in Kraka´s bow we have two flat acrylic viewports.
The sensor was placed on the INSIDE of the one viewport,
and in very intimate contact with it. The
cable was pulled back to the controlroom and secured so that its not
mechanically disturbed.
Then our black u-boat sailed into the indeed
very black harbor and submerged. The boat leveled out at 18 foot
of water and the device was turned on...WOILA...very low noise...I can hear
any sound generated in the boat - a relay clicking
- if I scratch the paint - the sound of a minute HP air leakin the sea
outside...any sound in the boat is heard very magnified. At this point
a challup form our
Royal Yacht "Dannebrog" - moored at in the harbor started its propeller - and
Kraka´s new listening gear immediately detected the sound contact...long before
I could hear it the "normal" way.
Once it got so close I could hear it directly
- the hydrophone was overwhelmed and made the noise I have complained
about.
Conclusion:
DolphinEar hydrophone are useful in submarines -
but must be installed with care. They are exceptionally sensitive to solid and
liquid transferred sound - and this was mis interpreted by me.
We now have to find out how its directional
characteristic is in this mounting - or perhaps improve it. Initially I
will place the other hydrophone in the starboard window and see what that
does to us...
In my opnion - there is a lot more to be learned
and lot more potential for these hydrophones in combination with underwater
recreational vessels. The sound dive was really fun.
Best regards,
Peter Madsen /
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