Technical Glossary

BBD Modulator –
BBD stands for “Bucket Brigade”, it is an analog chip that provides an amount of time delay based on the number of stages in it. BBD’s have been, and still are, used to create various analog effects such as chorus, flanging, phasing, and analog delay. In some Leslies this technology is used to create a simulated rotary effect for the low frequencies to save weight and mechanical parts.
Compression Driver –
High frequency speaker which produces sound via a diaphragm. By it’s self it is not able to project sound very well, it is therefore always attached to some sort of horn shaped resonator to project sound. In normal stationary speakers, such as PA speakers, the horn is mounted in a fixed position. In a Leslie cabinet this resonator is the upper rotor, referred to as the horn. See Horn.
Drum –
A rotating circular deflector which spins on the output side of a traditional speaker.
Horn –
A rotating horn shaped projector which is placed over the output side of a Compression Driver. (AKA Treble Rotor)
Merc-O-Tac –
A mercury filled rotary contact, see “Rotosonic Drum”.
Multi Rank Effect –
A simulation of the natural fullness of tone found in a pipe organ when 2 or more stops are played at once. In a pipe organ this is caused by slight inequities in tuning between 2 or more pipes. See Space Generator.
OEM Leslie –
A small single rotor Leslie made for installation inside an organ. Manufacturers would purchase these units from Leslie and then install them in their organs. They came in many styles; Horizontal Mount, Vertical Mount, 2 speed, 1 speed, Wood Rotor, Foam Rotor, Rotosonic Drum (w/ 6″ x 9″) and a range of speaker sizes from 8″ to 12″ all depending on the purchasers specifications.
Rotor –
Either a rotating Drum or Horn. See Drum and Horn.
Rotosonic Drum –
A rotating drum which has the speaker mounted *inside* it. The speaker is traditionally a 6″x9″ however 5″x7″ drivers were also used on occasion. These drum speakers are connected to the amplifier via a “Merc-O-Tac”.
Space Generator –
A versatile system using a scanner not unlike a Hammond Vibrato Scanner. It utilizes only 4 sets of plates in it’s rotation, with each set connected to a different delay circuit. The result is a vibrato-like effect when the scanner is rotated at a constant fast speed. Some units generate a Celeste or chorus effect by turning slowly, while some simulate random motion by being turned by an eccentric wheel.