Don Leslie invented the rotating speaker in 1937. His design is simple and elegant: an internal 40-watt tube amplifier feeds a speaker crossover, which splits the signal.
All frequencies below 800 Hz go to a 15” bass speaker and all frequencies above 800 Hz go to a compression horn driver.
The large bass speaker is bolted to the cabinet and a foam drum directly below the speaker reflects the bass outward.
For the high frequencies, a treble horn with two bells reflects the sound from the compression horn driver located below.
Then, of course, it spins. Separate belts, pulleys and motors drive the upper treble horn and the lower foam drum. Adding to the effect, the upper horn and lower drum spin in opposite directions. Most rotating speakers feature two sets of motors, allowing both slow (“Chorale”) and fast (“Tremolo”) rotation speeds.