Anders Heerfordt wrote: >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: +1 206-297-1310 [EMAIL PROTECTED] http://www.cetaceanresearch.com Cetacean Research Technology a strategic partner of Sound Technology Inc. Spectra Group - Signal Analysis Division
