The Frame
The frame is simply 1 to 1–1/2 inch tubular steel- either
round or rectangular-shaped in a rectangle and welded together at
the (preferably mitered) corners. Simple angle iron could be used,
if absolutely necessary.
The frame should be reinforced by three transverse beams (Figure
2). Near both sides of each of the four corners (eight all together),
weld flat pieces or slats of steel, which may be channeled for extra
strength.
Figure 4. With the plate carefully positioned
on the frame, both the frame and the plate may be marked so the
holes will be properly aligned with the hooks.
*[Joe Errico and I enhanced the design by adding 2
extra tensioning slats in the center of the long dimension of the
frame, to assist in the tuning of the plate]*
These should extend 1-1/2 to 2 inches beyond the frame, and
be about 1 to 2 inches from the corners (Figure 3). Holes will also
be drilled in the center of each of the slats. To determine the
exact placement of the holes in the slats and in the plate, as well
as the exact measurement of the length of the tubular steel for
the frame, you must make sure the plate and the frame line up together.
Make the inside measurement of the frame 1 to 1-1/2 inches larger
than the dimensions of the plate. Then lay the plate on top of the
frame. On the plate, mark the eight spots where the holes will be
drilled. Then mark the frame where the eight slats will be welded.
Next, mark the slats where the holes will be drilled (Figure 4).
When all the holes are drilled and the slats welded in place, paint
the frame to stop rust and corrosion.
The next step is to suspend the plate in the frame. EMT used spring
clips that held the plate in place and were also used to determine
tensioning. These are weak, and often snap. One of the improvements
made by most plate manufacturers was to use stronger, heavier clips
or hooks. Ecoplate used clips similar to those that secure fiber
straps used on packages. We will use simple, tempered, hardened-steel
hooks, threaded on their shafts.*[Joe and I now utilize
fiberglass clevis yokes with machine shop quality allen bolts to
better control the tensioning and Plate/Frame isolation] *
If the hook is plastic-coated, and hard-rubber and metal washers
are used, the plate and the frame can be totally isolated as far
as direct metal-to-metal contact goes.
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Figure 5. Detail showing correct
positioning of suspension hook. (left) and the high quality
yoke offered in the kit.
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To suspend the plate,
you will probably need help getting the hooks through the
holes in the plate. Slip the shaft of each hook through the
holes in the slat; thread the washers and a nut of the correct
size on the hook shafts, and hand-tighten all nuts (Figure
.5). The plate can now be suspended from the frame.
Now comes the subjective and fun part of the
project-mounting the driver and pickups, and tuning the plate. |
The Driver
EMT, Ecoplate, and Lawson all used similar drivers. A bullet-shaped
metal moving-coil "slug" is screwed into the plate. Two
wires carrying the signal go to the coil and it is suspended in
a large, heavy, circular magnet (Figure 6). It is important to be
sure the moving coil assembly does not rub or touch against the
sides of the magnet. The coil and magnet are aligned using a plastic
alignment disk. The procedure is delicate, and transporting the
unit sometimes misaligns the driver/magnet assembly.
Figure 6. Driver detail, as used on several
commercially-available plate systems.
Stocktronics and Audi-ence both used a wire rod attached to the
plate on one end, and to the voice coil of a speaker on the other.
It can be moved with no realignment, since there is plenty of "play"
in the movement of the rod, and this is restricted to within limits
by a rubber guide.
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Figure 7. The specially designed
driver
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The system we will
use is similar to both, but unique unto itself. It is also
one of the main reasons that this plate can be built so reasonably.
This design uses a specially designed driver-similar to what
used to be offered as a "coneless speaker" several
years ago. Whatever the driver is attached to becomes the
"sounding board" and vibrates enough to reproduce
sound. Therefore, if screwed into a door, that door would
become a "speaker." The specially designed driver
(see Figure 7) is an improved version of the coneless speaker.
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To install the driver, simply drill a small hole, the size for
the screw on the driver, in the center of the plate 2-1/2 inches
off to one side of the center of the beam of the frame. Screw the
driver in the side of the plate, with the frame reinforcements toward
you, about half way until tight. Attach a speaker cable to the two
terminals on the driver. Be neat and run the cable down the reinforcement
with "ty-raps" or tape. Now the fun begins. Move the plate
into your studio. Make sure the plate is standing upright. Connect
the other end of the speaker cable attached to the driver to the
output of your cue (headphone), or dedicated tube, class A, MOSFET,
etc., amp. Put on a tape with a steady snare-drum track or a constant
vocal track. Send only the selected track to your cue and, voila,
the signal will be heard on the plate. Assuming it is the snare
track, what you should hear is a thunderous snare sound similar
to "Bridge Over Troubled Water" or "The Boxer"
by Simon and Garfunkel (although I think they used an elevator shaft
for their reverb chamber). But, anyway, congratulations! You have
a working plate reverb! Now comes the real fun part-using your opinions,
taste, and ego to get it to sound just the way you want. This will
require your choice of pickups as well as tuning and equalization.
Talk Plate Reverb with Bob
Buontempo in his PSW Rec Pit forum.
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