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 __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>