-----Original Message----- 
From: Christopher Chapman 
Sent: Thursday, December 16, 2010 5:00 PM 
To: psnlist@.............. 
Subject: Re: Geophone Damping Mass Slew rate 


PREVIOUSLY:
3. It seems to me that seismic noise rarely hits the resonant frequency and 
  you might do better to not increase the damping over what already 
  is there in the mechanical and physical sense ?

    No. The critical damping allows you to get an output voltage flat with frequency above the resonant frequency. 

**********************************************************************
NEW:

I understand that voltage increases with velocity, this means to me,
given a constant amplitude,
The voltage will increase in a linear fashion with frequency ?
When properly damped with close to 4X Rseis Coil,
It means the MECHANICAL AMPLITUDE will be even
over the resonance but voltage will increase like N=1.
Furthermore, This voltage increase will somewhat
compensate  the lower end.
Meaning for the low frequencies,
you need only N=1 compensation to offset this
sensitivity problem under resonance ?

But still I see a null in the noise at 0.75 to 1.5 Hz.

Is there a problem with my geophone,
or is this a real phenomenon of
seismic noise, or
is my gain set so low that
I simply see no 1Hz noise ?

Also, Is it better (more proper) to look at
the bandwidths as 2 seconds (0.5Hz) to 2 Hz
or 0.2 Hz to 2Hz ?
I understand you can't just half the bandwidth
then sum it to the Fc to get the limits ?

The formulas for radio seems fine for
sub-sonic ?


4. Does the rate at which the geophone mass drop under heavy damping represent some new fundamental Eigen frequency?

    No. The resonance is determined by the mass of the armature and the spring constant. 


Does the rate at which the geophone mass drop under heavy damping represent  a limit in the slew rate ?
The mass will not move faster than that under 1G of acceleration related force.



5. Can anyone provide me with high school math models which represent the mechanical and electrical behaviors of the geophone? 
  High school math being trig and algebra minus the calculus?

    The theory is freely available on the Internet.

Yes Sir, but like a mathematician (PhD. thinks and not a first year college student (Layman).
They seem unwilling or unable to simplify for the non-mathematicians.
Not everyone wants to know the fine details which takes years to know.
Human knowledge is meant to be built upon.
Not to be a dictator of human life.
I just want a formula to give me the answers and not how it was
all derived.

an Eigen freq not contained in EQ signals then do no damping at all? 
This [little damping] should work for weak EQ signals and not close strong ones ? 


      An undamped geophone has a single frequency peaked response - definitely NOT what you want!   

I have found in the past if you filter at the peak Fc Filter at the peak Fc of the geophone  you can get the low or high end
response ( not both) electronically with very sensitive results. I'm speaking teleseismic events
more so than regional.
Have you ever seen a narrow frequency seismograph ?
Like only 1 Hz ?
Like several narrow bands ?
Like a spectrum analyzer as a receiver ?
Not sure I'm clear here.




     Regards,


     Chris Chapman

Happy Holidays,
geoff



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