PSN-L Email List Message

Subject: Re: Homade Geophone
From: "Geoff" gmvoeth@...........
Date: Fri, 5 Aug 2005 20:07:06 -0700

The idea is to obtain a free period of one second or more
0.5 would be ideal are you able to control the free period of your
'meter movement Geophone' and if so how did you do it ?

I have found you need a pendulum of 12 inch length and also a
spring will behave according to the formula for a pendulum
so like if you need a free period of one second for a spring
then whatever mass will stretch the spring by 10 to 12 inches
will give it a free period of one second or more.

If you could build a spring with tension already built in
you might then  suspend a mass that will hang only 1 or more
inches instead of 10 or 12.

Getting the proper free period to do the job is the hardest
part of making the Geophone especially if it is vertical.

Without the proper free period the gain necessary to see
those lower frequencies is too high and you run into
all kinds of sensitivity problems with other electrical noises.

Or so it seems to me.



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