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Questions about hydrophones

T

TIMO PARRU

Jan 1, 1970
0
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
 
R

Robert Baer

Jan 1, 1970
0
TIMO said:
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

Nickel and alloys can also act as transducers; wire in some power
potentiometers can be used for starters...
 
C

Chris

Jan 1, 1970
0
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?

Piezo has a good linear response and doesn't mind being potted
and/or can stand getting wet. They also don't mind the static
water pressure that you get from depth.

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?

If you have air in the gap, you'll get a bit of distortion and a poor
response. Best method is to 'pot' the crystal or piezo in something with a
Rho-C roughly the same as water to minimize the impedance mismatch. For
DIY stuff, silicon rubber is probably just fine.

Take a small waxed paper cup, hang the wired piezo (and amplifier circuit
if you want) in the middle and fill with silicon. Peel cut off afterward.
A cheap caulking gun tube of clear silicon goes for $2 at Walmart.

-Chris
 
T

TP

Jan 1, 1970
0
Chris said:
Piezo has a good linear response and doesn't mind being potted
and/or can stand getting wet. They also don't mind the static
water pressure that you get from depth.

Is that true that piezo has a good linear response? The piezos Radioshack
sells
has about 30dB variation over range when using it to produce sound.
 
N

N. Thornton

Jan 1, 1970
0
TP said:
Is that true that piezo has a good linear response? The piezos Radioshack
sells
has about 30dB variation over range when using it to produce sound.

Thats frequency response, which is a different thing to linearity.

Regards, NT
 
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