This photo shows the boom (~30 inches long), the lead weight (~5 pounds), the pick-up coil, magnet, vertical and horizontal damping. The pick-up coil is from a 220 VAC relay. The vertical damping is a piece of PC-Board material (5 x 3 inches) horizontally suspened in mineral oil and is used to to stop high frequency vertical oscillations. The horizontal damping is a 4 x 4 x 1/8 inch piece of cooper between two attracting magnets. All magnets are simulare to the Edmund Scientific part number B41,949 with a 25 pound pull. The magnet on the boom is attached using super glue.
Larry Cochrane - www.seismicnet.com/contact.html