In a message dated 02/06/2009, gmvoeth@........... writes:

Do you  really mean Q of 0.7
Which is a Damping of 1/0.7 ?

If I make a  filter with a damping of only 0.7 I get a peak in
the roll off response  instead of a Butterworth profile ?



Hi Geoff,
 
    You set the damping of a Lehman to 0.7 x  Critical value and also on a 
geophone.
    You are providing a force from the frame to the  mass which is LESS 
than that required to damp it fully.
    This gives about the best compromise for  the response amplitude / low 
frequency corner. The rise in the  characteristic is only just visable. 
    You loose signal amplitude rapidly as you increase  the damping over 1.
 
    Regards,
 
    Chris Chapman






In a message dated 02/06/2009, gmvoeth@........... writes:
Do you 
  really mean Q of 0.7
Which is a Damping of 1/0.7 ?

If I make=
 a 
  filter with a damping of only 0.7 I get a peak in
the roll off respon=
se 
  instead of a Butterworth profile ?


Hi Geoff,
 
    You set the damping of a Lehman to 0.7 x=
 
Critical value and also on a geophone.
    You are providing a force from the frame to=
 the 
mass which is LESS than that required to damp it fully.
    This gives about the best compromise for=
 
the response amplitude / low frequency corner. The rise in the=
 
characteristic is only just visable. 
    You loose signal amplitude rapidly as you inc=
rease 
the damping over 1.
 
    Regards,
 
    Chris Chapman