If this is wrong group to ask about hydrophones, let me know what is better.

1) In all DIY projects hydrophones are made based on piezoelement. Why
piezo?
2) Normal (easy) way to do it is to sandwich piezo between two plexiglass
(3-4mm) discs and put o-ring inbetween.
- How thickness of plexiglass affects sound quality and performance?
- How air volume inside 'sandwich' affects sound quality and
performance?
3) What would be good link to find more info?

/timo

TIMO PARRU wrote in message
...
If this is wrong group to ask about hydrophones, let me know what is
better.

1) In all DIY projects hydrophones are made based on piezoelement. Why
piezo?
2) Normal (easy) way to do it is to sandwich piezo between two plexiglass
(3-4mm) discs and put o-ring inbetween.
- How thickness of plexiglass affects sound quality and performance?
- How air volume inside 'sandwich' affects sound quality and
performance?
3) What would be good link to find more info?

/timo

ASDIC/SONAR (UK/US) echo sounders use Lead Titanate Zirconate Piezo-electric
elements because these are better suited to transmission of high energy
ultrasonic pulses. Do a Google on "Lead Titanate Zirconate" and "Hydrophone"
for more info and suppliers.

If by 'Hydrophone' you mean an underwater microphone, then Piezo-electric
elements can also be used, but an ordinary mic cartridge in a watertight
housing would also do - unless you're specifically looking for ultrasonic
signals from fish for example.

If the housing were filled with something inert like silecone oil this would
improve the water-mic coupling. Check with the microphone manufacturer first
to make sure the oil would not cause damage.

The cheapest Piezo-electric elements you can get are the discs used in small
Piezo bleepers. They consist of a thin sliver of LZT bonded to a metal disc.
Many component suppliers stock them and they only cost around 25p. They're
interesting things to experiment with.

If you're interested, here's a less well-known use for Lead Titanate
Zirconate Piezo-electric transducers. I used to work there until shortly
after the Far Eastern market collapsed! -

http://www.cnsfarnell.co.uk/CNSF_English/concrete.htm

It's all first-class equipment BTW - and no, they're not still paying me!
)

Hope this helps,

Nemo