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.

Figure 5. Detail showing correct positioning of suspension hook. (left) and the high quality yoke offered in the kit.

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.

Figure 7. The specially designed driver

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.

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.