The SpectraTone II is an effect that was on some Wurlitzer Organs, similar to a Leslie rotating speaker on Hammond organs.

I removed the SpectraTone speakers from an old Wurlitzer and am attempting to build a Guitar speaker cabinet out of it.

In the photo, you can see a pair of 4″ speakers mounted opposite each other in a can connected to a counter-balanced arm.  The assembly spins at two different speeds, because the SpectraTone has two different motors!  This was on a crossover with two 12″ speakers, so only the higher frequencies were spun up.  It’s pretty cool.