Construction of the Unit

As mentioned in the introduction, the design of this unit will incorporate your mixer and cue (headphone) system as all the electronics that are required. We will mostly concentrate on the construction of the mechanical system and the transducers-the frame, plate, driver, and pickups.

Figure 2. The tubular steel frame is reinforced with three transverse support beams.

This is probably the most critical of all the steps involved in the process, so be careful. The plate is actually "the instrument" used for the reverb, so it should be chosen as if it were a fine acoustic instrument. EMT used a one meter by two meter cold rolled steel plate approximately 1/64-inch thick. Lawson, who manufactured "The Plate" (LP1 and LP2), used basically the same size plate, but it's a little thinner. On the other hand, some manufacturers used stainless steel. The Ecoplate by Studio Technologies used approximately the same gauge in stainless, as did Audi-ence, while DB Cassette of Sweden, who manufactured the Stocktronics Plate, used a stretched, hardened piece of cold-rolled stainless approximately 0.03 inches thick. The question of what kind of steel to use is totally subjective. Reasons claimed for using stainless steel include consistency, high density, and the fact that it's tarnish proof, while regular steel users claim smooth, more natural sounding reverb and a less "metallic" decay. Only you can decide what sound you prefer.

Befriend your local steel warehouse owner, bring two associates, and prepare to listen. Most steel sheets come in 3-foot wide sheets; this is close enough to one meter for our purposes. The length, however, is usually eight feet long and cutting charges to make it six feet might be added to the price of the steel. Some places also have minimum orders, so try to buy your plate and frame materials from the same source to save added expense. If the owner of the shop will allow-and it's worth a healthy tip to have him help you out-have your two friends hold the sheet of steel horizontally as tight and still as possible, such that it doesn't "thunder." Tap it in the center with a key and listen for a "sizzle" and long decay in the high frequency, as opposed to a "clangy" sound. The delicacy and length of the high frequency decay are what you are really after, since the bottom and mids can be dealt with more successfully by tensioning. Try several pieces of different types until you find what you want. Be selective and take as much time as possible, because this is the heart of your system and you must be happy with it.

Figure 3. Corner detail, showing triangular reinforcement plate welded in place. (Reinforcement is the same thickness as the plate)

Including the cutting, the steel sheet should run between $50 and $100, depending on the type you choose. Reinforcing the corners by spot welding a triangular piece of steel on each one is the recommended procedure. For corner-cutting by the cost conscious, however, it's not totally necessary, since it could run $25 to $50 additionally. But, it really should be done if at all possible, because the plate will be put under heavy tension, and holes will be drilled in those corners later in the plate-preparation procedure. The holes should be drilled after the frame is completed, so a more "custom" fit may be made.

Including the cutting, the steel sheet should run between $50 and $100, depending on the type you choose. Reinforcing the corners by spot welding a triangular piece of steel on each one is the recommended procedure. For corner-cutting by the cost conscious, however, it's not totally necessary, since it could run $25 to $50 additionally. But, it really should be done if at all possible, because the plate will be put under heavy tension, and holes will be drilled in those corners later in the plate-preparation procedure. The holes should be drilled after the frame is completed, so a more "custom" fit may be made.

Talk Plate Reverb with Bob Buontempo in his PSW Rec Pit forum.