JBL W12GTI Owners Manual English - Page 4

The Official Brand of Live Music Enclosure Construction Please observe the following suggestions when building an enclosure for GTi Series subwoofers. 1. Choose an enclosure design from the Enclosure Design Sheet included with your subwoofer. 2. Use at least 3/4" (19mm) MDF (medium density fiberboard) or marine birch plywood to build the enclosure. Enclosures for 12" and larger subwoofers and smaller woofers driven by high-power amplifiers should be constructed using 1" (25mm) material. 3. Join pieces of wood with glue and screws; do not use nails. Once the box has been tested, seal all joints inside the box with silicone caulk. 4. Fill the enclosure with damping material (dacron, fiberglass insulation or long-fiber wool) according to the design you have chosen from the Enclosure Design Sheet. "0% fill" indicates that no damping material should be used; "50% fill" indicates that all interior walls except the baffle should be lined with 1" thick damping material, and "100% fill" indicates that the box should be loosely stuffed with damping material. 5. Use PVC or ABS plastic pipe for ports. Keep in mind that the openings at either end of the port must be at least one port diameter away from any obstruction. 6. Use the 10/24" machine screws and T-nuts provided to mount the woofer to the baffle. See Figure 1. Figure 1. Mounting the GTi woofer in its enclosure Dual Coil Versus Differential Drive® (patent pending) Conventional dual-voice-coil woofers use a pair of voice coils "interwound" on the former and centered in the magnetic gap. The two coils may be connected in series or parallel in order to maximize an amplifier's output power. Both coils drive the cone forward and rearward. Xmax (one-way-linear) is determined by the amount of voice coil exposed above and below the top plate. A conventional voice coil is made up of several layers of windings, each transferring heat to the winding next to it until the heat is finally dissipated by the outside layer through the top plate, magnet and backplate. This arrangement is inefficient, and results in low thermal power handling. See Figure 2. 10/24" SCREWS (PROVIDED) T-NUTS 04 (PROVIDED) Figure 2. Conventional dual-voice-coil design BOTH COILS DRIVE CONE FORWARD AND REARWARD CONE SPIDER OVERHANG DETERMINES Xmax TOP PLATE MAGNET POLE PIECE / BACKPLATE JBL GTi Series subwoofers employ Differential Drive, a technology developed by JBL Professional. Differential Drive employs two voice coils positioned at opposite ends of the former, each suspended in a separate magnetic gap. These two coils may be connected in series or parallel, like a conventional DVC woofer, to maximize an amplifier's output power. Both coils MUST be connected to the amplifier in correct polarity! At low power, both voice coils drive the woofer's cone, and any motor nonlinearities are cancelled by the out-of-phase coils and gaps. As power input increases so that one coil rides completely out of its gap, force is still applied to the cone by the other coil. At extremely high power, each coil will enter