Hi Chris

I think we agree that the damping resistor is not important for
frequency response below the resonant frequency.

My goal is get AS1 equivalent performance out of a 4.5 Hz geophone,
so I need to go to 1/100 of the resonant frequency, all the way down
to 0.045 Hz in the range of surface wave frequencies.  I am not sure
that the Roberts circuit is up to that.

I have a very simple circuit that approaches that performance as you
can see by my sample detections, including spectra, listed below the
helicorder plot on my page

http://www.infiltec.com/seismo/qm45.htm

I think that you can see from these detections that my 4.5 Hz geophone
system has good performance from 1 Hz all the way down to surface waves
near 0.04 Hz.

Ciao,

Dave


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