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Choosing a Hydrophone

2.2 Frequency Response
A hydrophone’s frequency response refers to the way a
hydrophone responds to different frequencies, i.e., the output
voltage at a given pressure amplitude with regard to frequency.
An ideal “flat” response means that the hydrophone is equally
sensitive at all frequencies without any regions of exaggeration
or attenuation. However, there are many design considerations
(e.g., inherent resonant frequencies, backing material, electrical
impedance) that make this a challenging goal to achieve.
Invariably, all hydrophones exhibit some deviation. It is common
to describe a hydrophone being flat within a given frequency
range within some tolerance. For instance, the HM membrane
hydrophone is flat from 0.5 to 45 MHz within ± 3 dB.
The plot below summarizes the useable frequency response for
different hydrophone models.

Hydrophone Model  HCT        ± 3 dB
                  HFO        ± 6 dB
                  HNA         TBD                                     100
                  HNC                 0.1 1 10
                  HNP                          Frequency Range [MHz]



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