Hammond Sk PRO, Справочное руководство

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ORGAN Voice Section
156
t What Are “Horn” and “Bass?”
The basic Leslie Speaker design, as represented by the 122 and 147 families of cabinets, divides the sound
between “treble” (above 800Hz) and “bass” (below 800Hz). The treble frequencies are routed to a treble speaker
or “driver,” while the bass tones sound through a bass speaker (typically 15"). In the classic design, the speakers
themselves do not move - a baffle is rotated in front of each speaker to produce animation. The shape of the
baffle for the high frequencies is similar to the bell of a horn, hence the popular designation “horn.” The figure
below illustrates this.
The Leslie cabinet type shown above connects to the organ console by means of a special connector kit which
allows proper routing of both the audio signal and the electrical voltage necessary to operate the rotors.
The first Leslie speakers used two motors to rotate the baffles at a speed suitable for recreating theatre-organ-type
tremulant which were controlled by a toggle switch on the side of the speaker cabinet. In the mid-60's an
additional motor was added to both Horn and Bass which spun the rotors much more slowly to suggest the
sound of a “celeste,” or a compound organ stop with two or more ranks slightly detuned. Also added were
switches which could be mounted to the front of an organ console to allow the organist to control the rotor
speeds, and therefore the sound, while playing- “Chorale” described the effect produced by the Slow motors,
while “Tremolo” was the designation used when the Fast motors were engaged. The picture below shows a
typical Leslie switch of this kind.
In more recent years there have been two important additions to the classic Leslie design:
1. The introduction of an 11-pin interface to allow a Leslie Speaker to handle more than one audio
channel, as well as to isolate line voltage from the audio signal path.
2. The replacement of separate Fast and Slow motors with variable speed motors for both Horn and
Bass. The newer motor design reduces the total number of motors from four to two, and also
allows for “Brake” mode, or the ability to shut the rotors completely off (previously a special “brake
kit” had to be added to the cabinet to permit this feature).
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SK PRO Reference Guide