David,
  Check out Lahr's message of yesterday--this is a slick variation of
the old Zollner suspension.  It looks to be easy to build and has got to
be frictionless.
  About boom length:I bought a Geotech SL-220 horizontal from ebay. 
This has a  <8 inch>  boom and can be adjusted up to 30 sec. period. 
This is proof positive that short booms can work fine.
  You should also look into using a resistor across the coil for
damping.  This is much simpler than oil pots or magnetic systems.
Bob


David Saum wrote:
> 
> > From:    "Bryan&Regina Goss" 
> > Date:    Tue, 12 Jun 2001 13:28:56 -0500
> >
> > I have read that a ball bering was used in place of a knife edge
> >........http://www.1goss.com/seis.htm
> 
> I read this also, so when I built my Lehman I used a ball bearing
> but I had trouble getting a smooth metal surface that it could
> rest against without making a dent.  So I used a vertical piece of
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