Hammond Model A, Руководство пользователя, Страница: 136 / 298

REVERBERATION CONTROL
Reverberation control is an important feature of any Hammond Organ installation.
This device is enjoying wide acceptance because it produces reverberation in
variable degrees so the Hammond Organ. when installed in an acoustically dead
enclosure, sounds very much like an organ played in a large acoustically live
church or auditorium where organ music. enhanced by considerable reverberation
sounds at its best.
Reverberation is the prolongation of sound by repeated reflections or echoes, and is
measured by the time required for a sound to become inaudible after the source of
sound has been stopped. It is present in some degrees in all enclosures, and music
is more pleasing to the ear when accompanied by some amount of reverberation. This
is particularly true of organ music.
Reverberation results from the fact that the longer path traveled by reflected
sound causes a delay in hearing the reflected sound waves. This is easily realized
in the case of sharp staccato sounds and a fairly distant reflecting surface, as the
delayed sound is then heard separately from the direct sound and is recognized as an
echo. When music is played in a large room however, the sound echoes and re-echoes
repeatedly until absorbed by the surroundings. The Hammond reverberation control is
an electro-mechanical device which introduces multiple echoes by means of
reflections within a network of coil springs and thereby provides adequate
reverberation in locations where the natural reverberation is not sufficient.
OPERATION OF FLUID TYPE
The fluid type reverberation unit (see figure 1), about 4 x 5 inches in cross
section and about 4 feet high, is connected to a reverberation preamplifier built
into the power amplifier. (In some models of tone cabinets the reverberation
preamplifier is a separate unit connected to the power amplifier by cables.) The
entire equipment is attached to the organ tone cabinet.
Reverberation is applied to the organ music after it leaves the console. Part of
the console signal goes directly to the power amplifier and part goes into the
reverberation channel, after suitable amplification.
The electrical signal fed into the reverberation unit is converted into mechanical
energy by a moving coil driver unit, similar to a dynamic speaker without a cone.
The mechanical waves are transmitted through coil springs, which have the
property of conducting sound vibrations much more slowly then the speed of sound
waves in air. In this way a spring of convenient length can introduce a delay
equivalent to that obtained in a large hall.
The driver unit, at the top of figure 2, introduces up-and-down vibrations into
the stirrup directly under it. The two enclosed springs under the stirrup hold
it in position but permit it to move freely up and down, and the spring at the far
left balances the pull of the others. These three springs are almost entirely
immersed in damping fluid, as they act largely as dampers to stabilize the response
of the driver and prevent undesired reflections.
1