Hammond Model A, Руководство пользователя, Страница: 142 / 298

OPERATION OF DRY TYPE
A later reverberation device. Figure 3. is an improved unit which employs a dry
damping means instead of the liquid previously used. It has improved
driver and pickup elements and has three transmission springs instead of the
one formerly used.
The device is about fourteen inches high. thirteen inches wide and two inches in
depth. It is incorporated in the new PR-20. PR-40 and QR-40 tone cabinets.
In operation. an electrical signal from an amplifier is applied to the driver
unit in the reverberation device which then converts the electrical signal into
mechanical energy which is fed into the three springs of different lengths. The
signal takes 1/22 second to traverse the shortest spring to the pickup, which
reconverts part of the energy to an electrical signal and reflects most of the
energy back along the spring to the driver, where again most of the signal is
reflected back along the spring to the pickup. This transaction continues until the
signal energy at the pickup is reduced to one millionth of its original value. This
period is about two seconds in duration. The other two springs operate in a similar
fashion. but their reflections occur at longer time intervals, 1/17 and 1/15 second
respectively. The amount of damping for each of the three springs is so proportioned
that they have a uniform decay rate.
OPERATION IN PR AND QR SERIES TONE CABINETS
The dry type reverberation device mounted in the PR and OR series tone cabinet
functions as follows. Part of the console signal is applied to the reverberation
driver and the resultant reverberated signal at the pickup is separated into two
frequency bands, one occupying the spectrum from thirty-two to two hundred cycles,
and the other from two hundred cycles to six thousand cycles. The low frequency
reverberated signals are mixed with the direct console signals. amplified and fed to
the low frequency speakers. The high frequency or treble reverberated signals are
amplified and fed to a separate speaker system, while the treble signals from the
console are also amplified and fed into another speaker system. In other words, the
low frequency direct and reverberated signals are electrically mixed and the
high frequency direct and reverberated signals are acoustically mixed.
Two selector switches are mounted on the side of the PR and OR series tone cabinets
to provide a variation in the amount of reverberation produced. The bass
reverberation switch provides increased direct output as the amount of reverberated
signal is reduced. This is accomplished by introducing more or less direct signal
into the bass channel as the amount of reverberation is decreased or increased. The
treble reverberation switch controls the gain of the treble reverberation amplifier
channel, but if the switch is turned to the Reverberation Off position, the direct
console treble signal is fed into this channel to provide full treble acoustic
output from the cabinets.
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