>Btw, by connecting a hydrophone, which typically has an impedance
>corresponding to 3 nanoFarad to a microphone preamplifier, which typically
>has an input impedance of 10 kiloOhm, you get a low frequency cutoff
>frequency at 1/(2 * PI * 3 nF * 10 kOhm) = 5 kHz. So you end up with a
>frequencyresponse, which is flat from 5 kHz to 20 kHz, which is not quite
>what you desired.
The capacitance and output impedance of hydrophones can be quite variable.
In addition, some hydrophones have integral preamplifiers, so transducer
capacitance is not important in deciding on which digital interface to
chose. For example, the Cetacean Research C10 and C13 hydrophones do not
have integral preamplifiers and their capacitance is ~9nF, which would
result in a low frequency 3dB point of 1768Hz assuming a sound card input
impedance of 10kOhm. However, the C54XR and the C304 hydrophones have
integral preamplifiers with an output impedance of 2.5Ohms. These
hydrophones will work with any interface unit without limiting the low
frequency response.
Joseph R. Olson
Cetacean Research Technology
PO Box 70186
Seattle, WA 98107
Tel/Fax: +1 2062971310
[EMAIL PROTECTED]
<a href="http://www.cetaceanresearch.com";
rel="nofollow">http://www.cetaceanresearch.com</a>
Cetacean Research Technology
a strategic partner of Sound Technology Inc.
Spectra Group  Signal Analysis Division
