Please contact me if you have any more good information.
There's some information at the SYR 4 site, the best of which is:
Also, some other reviews and mentions:
This piece was commissioned by Sonic Youth, and it's the only such piece on the album (all others were composed earlier). It looks like Oliveros doesn't say anything special about it on her web page, but there you can find out more about her schtick.
Pauline Oliveros' home page
Essentially, the process is: swing microphones over loudspeakers, and record the resulting feedback. Since the oscillations (of the pendula) must damp and thus cease, you can guess at the results.
An article (in German, unfortunately) on the piece (translation forthcoming, possibly - babelfish does a bad job on it).
But! My friend Brynne has been kind enough to provide a much-better translation of a portion:
Such conceptual concentration of the musical works on the structurally simple way of his generation shows itself particularly in Reich's Pendulum Music for Microphone, Amplifier, Loudspeaker and Performer (1968). Here three, four or more microphones at a time are hung from their cords in an arrangement above a loudspeaker. The amplifiers are set so that in the rest position, a feedback results, which is silenced when the microphone is moved away from the arranged loudspeakers. The performer does this by performing. They guide the microphones and cables as if they were pendula and let them begin to swing all at once. So begins a sequence of feedback noises until the microphones finally come to rest over the loudspeakeres and the amplifier is disconnected.
The verbal score of Pendulum Music includes another technical statement, which does not describe further the desired musical result of the composer. As in a physical experiment, only the experiment construction and the beginning parameters are given, which no doubt lets a given progression be expected, but is not described in detail. Each performance is only there once and is not reproduceable. Differently than in Piano Phase and the Toneband Pieces, the change of the phase relationship is not composed. This results from the lengths of the pendula and the characteristics of the suspension and is not to be further influenced by the performer after the conclusion of the construction. Having placed and released the microphones, there remains no influence from him on the proceedings and it will show to listeners: "When the trial is erected and released, it is driven by itself." (7) Completely similar to what John Cage wrote: Reich in this time wrote not pieces in order to fix a sound or musical idea, but to hear the process inverted, as to represent the creative process in the conversion of sound.
The process is also mentioned in this paper on the major minimalists.
Biographical information and selected discography
A fairly complete-looking discography
Biographical information and works list
Information on some other works
Review of a Tenney disc, including an interpretation of this piece
on Maciunas' musical and non-musical life
Slonimsky is more famous in the jazz world because John Coltrane adopted his Thesaurus of Scales and Melodic Patterns as a study source. He was also an earlier experimenter with electronic instruments, having received Leon Theremin's second "Rhythmicon", a keyboard instrument built on principles similar to those of the Theremin.
Some information on Cardew extracted from the Eno list. Among other things, he wrote a book, Scratch Music, of brief instructions quite similar to Eno's own Oblique Strategies.
biographical information from a UK site