Leslie speaker
A Leslie speaker is an organ cabinet that introduced the Rotary effect which was invented by Don Leslie, who wanted to replicate the sound of a pipe organ. It is often associated with a Hammond Organ, but it has also been used as an effect for other instruments. 1
The Leslie cabinet contained two parts: a rotating deflective drum for low frequencies and a dual horn assembly for the high frequencies. Leslie speakers get their distinctive sound from reflective surfaces and the Doppler effect that it creates. 1