Page 18 - HydrophoneHandbook_eReader_Ed2_20151208
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Hydrophone Handbook

         Choosing a Hydrophone

2.3 Pressure Range
Sensitivity
There are several design considerations that contribute to the
sensitivity of a hydrophone. Factors such as the sensing
material, size, construction, and electrical noise will vary with
different hydrophone models. Selection of the best hydrophone
will require some knowledge of the nominal acoustic output
level of the application. A rule of thumb is to ensure the
measured amplitude is at least 5 times higher than the noise
equivalent pressure (NEP) of the hydrophone to maximize the
signal to noise ratio (SNR).

The NEP of the hydrophone can be estimated by the following
expression:

  {}  =      {}                      ×  1000
                                          {} × 

Onda hydrophones include an End-of-cable Open Circuit
Sensitivity, or EOC sensitivity, with the exception of HM
hydrophones which are calibrated at 50 ohms because of their
integral preamplifier. To increase the sensitivity, the
hydrophone can be connected to a preamplifier which adds the
preamplifier gain (typically flat in the frequency of interest) to
the sensitivity of the hydrophone. Onda preamplifiers, which
are designed as a buffer amp, allow for the addition of a 50 ohm
cable without altering the calibration significantly.

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