The Gyrophonic Projector is a rotating speaker system whose design is different to that of the widely popular Leslie speaker. The unit produces organic sounding tremolo effect useful as a creative tool on many different sources.
While a Leslie speaker had a fixed speaker cone and a baffle that spun in front of it, the Allen system placed a set of speakers on a large wooden disk which was rotated. You can tell if your organ still has the original gyrophonic system if you stand next to the speakers. You will hear a clicking sound which comes from commutator brushes that route the signals onto the rotating disk.
The Gear Rack