Environmental sound sculpture devised in 1973 by the American pianist and composer David Tudor. It was based on the concept of the ‘instrumental loudspeaker’, which Tudor developed in 1966 and used in all four works in the Rainforest series, starting in 1968. The first instrumental loudspeakers consisted of containers into one end of which electronic or other sounds were fed through small loudspeakers. The sounds were picked up by microphones at the other end and passed to a conventional sound system. The containers in these early examples were metal boxes into which various materials were introduced to filter the signals acoustically as they passed between loudspeaker and microphone. In Rainforest IV the boxes are replaced by a great variety of objects, many of them in everyday use or scrap materials, to which loudspeaker-like transducers are attached; together these create an elaborate sound environment, which is operated by members of the group Composers Inside Electronics (founded by Tudor)....