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The Leslie Cabinet
Don Leslie developed his rotor cabinets in 1937, and began marketing them in 1940.
Laurens Hammond wasn’t keen on the concept of rotating speakers at all.
Leslie’s approach was to simulate a variety of locations in the pipes (as in pipe organs),
resulting in a new spatial perception for every note. The rotor speaker cabinets could
simulate this effect, and the sense of space that they impart is incomparable, when placed
side-by-side with any fixed speaker. The periodic undulations in sound and volume, and
the vibrato caused by the Doppler effect (see below) aren’t all there is to the Leslie
sound—it’s the spatial effect, too.
The “classic” Leslie speaker design features two drivers—a treble driver with horns (only
one works, and the other simply acts as a counter-weight) and a bass driver. The horns
of the treble driver and the sound baffle of the bass driver are physically rotated by electric
motors.
As the speakers rotate towards the front of the cabinet (the listening position), then
towards the back of the cabinet, you will hear a “Doppler effect”—where sounds become
louder and brighter as their position changes. To give you an idea of this effect, it is much
like the sound of a train going past if you were standing on the platform. On approach,
the sound is muffled; but then it becomes both louder and brighter as the train passes,
and finally it becomes more muffled as it moves away from you.
The rotating driver/sound baffle can be switched between two speeds—fast/tremolo or
slow/chorale (or stopped completely with a mechanical brake). The transition between
the two speeds, or the use of a fixed speed, produces the characteristic “Leslie” vibrato,
tremolo, and chorus effects.
The first Leslie, the model 30, had no chorale—just tremolo and stop. The chorale idea
(which came much later) was born of a desire to add a vibrato to the organ. Chorale,
which offers far more than a simple vibrato, was first introduced to the market with the
122/147 models. At this time, Leslie also added the “Voice of the pipe organ” label to his
cabinets.
It wasn’t until 1980 that the two companies and brand names came together, six years
after the last tonewheel organ was built. Mechanical Leslie rotor cabinets are still being
built today, by the Hammond-Suzuki company.
182 Chapter 7 EVB3