In his own words (1992): "Music on a Long Thin Wire is constructed as follows: the wire is extended across a large room, clamped to tables at both ends. The ends of the wire are connected to the loudspeaker terminals of a power amplifier placed under one of the tables. A sine wave oscillator is connected to the amplifier. A magnet straddles the wire at one end. Wooden bridges are inserted under the wire at both ends to which contact microphones are imbedded, routed to the stereo sound system. The microphones pick up the vibrations that the wire imparts to the bridges and are sent through the playback system. By varying the frequency and loudness of the oscillator, a rich variety of slides, frequency shifts, audible beats and other sonic phenomena may be produced."
However, Lucier admits a long thin wire is only used to impress, a short thin wire would have worked as well if not better, and he discovered that the best way to produce variation in the sonic phenomena was to pick a setting and leave the setup alone. He praised David Rosenboom for his ability to pick interesting settings. -Wikipedia