Briefly, you've got a pair of speakers that can spin. They are driven
by separate motors. At slow speed they run at about 25-30 rpm, at high
speed they run at about 360-400rpm (around 0.3-0.5Hz and around 6-7Hz
modulation rate). The two motors are unsynced and take different
amounts of time to spin up.
Nice email. There were also a lot of modified cabinets such as a single
spindle as some users did not like the unsynchronised sweeps, they felt
there was more depth with a single rotation so decoupled the horn motor and
linked them up to the bass spindle.
Some preferred alternatively to just remove the bass motor all together as
the thing did tend to be slow starting - with just the horns sweeping there
was generally better response from the cabinet for a degree of lost leslie
quality that was often lost in the mic positioning for live work anyway.
There were also modifications that added a breaking system, at least to the
bass spindle, to get it to slow down at a reasonable rate.
Some Hammond users were also known to put a belt 'break' on the main
tonewheel motor to get pitch bend out of the actual organ although I think
that was generally frowned upon as it was a mains AC synchronised motor that
did not originally autostart - it needed a separate 'starter coil' to make
it spin in the first place.
Bristol emulates all these features, albeit in a cheesy sort of way. They
are all reasonably easy to build into the algorithm once you have the signal
separated into the high and low speaker rotation algorithms.
Nick.
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