The term Polyphone can mean, in translation from the Greek, ‘many sounds’, and in practice is applied to musical instruments (or compositions) which produce more than one sound at the same time. This was a particular issue for the developers of early synthesisers, when available computing power was far more limited than today. The term is used also in the development of early music, and for cellphone ring tone technology. 

Organ builders use the term more specifically to refer to organ pipes which can produce more than one note. though not simultaneously. Bass pipes are resource hungry, in terms of materials, cost and space. Adjacent pipes are, almost, never played at the same time, so a means of making one pipe serve the function of two (or even more) is very attractive in enlarging the resources of an instrument at minimum expense. 

Probably the most widespread user of the polyphonic principle was John Compton, in the 16′ Tibia octave on many of his cinema organs. Instead of the usual 12 pipes, there were 6 pipes each equipped with a small pallet in the side of the pipe and leading to a very short tuning pipe emerging from the front of the main pipe. Thus equipped, the pipe could play two adjacent notes. With the valve closed, the pipe would play its fundamental. With the valve open, the pipe would play a slightly higher note, tunable by means of a tuning slide on the short pipe. These particular examples were very successful, due partly to the lack of harmonics from the wide scale pipes. 

Other notable examples were John Compton’s 32′ Cubes and Polyphone pipes. The Wurlitzer company – not normally noted for this sort of innovation – also tried similar ideas on three sets of 32′ Diaphone pipes. In this case massive trap-doors, operated by a herculean system of ropes, levers and giant power pneumatics, were deployed to change the tuning of pipes so that 6 pipes did the work of 12. Somehow, when considering such cunning devices, one is left feeling that on this occasion the house of Wurlitzer came second to the wizards of Acton.