Detailed Information:

The W7 voice coils are huge and by far the largest JL Audio has ever made (in diameter and winding height). The massive surface area of these coils is excellent for heat dissipation, while the huge winding height provides the necessary motivational force to achieve the huge excursion of the W7 designs.

Considering their size, the W7 voice coils are extremely light in weight. We use aluminum-alloy wire (instead of conventional copper) and a specific winding method to achieve the electrical properties that we deemed necessary to achieve our design goals. The light weight of the coils helps keep the overall moving mass down at manageable levels, which is extremely important for efficiency and sound quality reasons.

The 8W7 uses a 2.25-inch diameter coil (2.0-inch winding height), the 10W7 uses a 2.75-inch diameter coil (2.3-inch winding height), the 12W7 employs a 3-inch unit (2.8-inch winding height) and the 13W7 enters battle with a 3.55-inch diameter voice coil (3.0-inch winding height). You may have noticed that, for three of the W7's, we chose non-standard coil diameters. Because of the complete design freedom afforded us by the fact that we were willing and able to tool everything for these speakers, we were able to precisely specify the diameters that would produce optimum performance for each model.

Since the W7 is an extreme excursion speaker with a detachable surround, voice coil former resilience is a key parameter. If the surround is roughly handled, the coil former could be damaged by contact to the pole piece. Kapton� is a high temperature polyimide film that snaps back from moderate deformation without harm. Aluminum, however, will bend readily and stay that way. If an aluminum bobbin is deformed badly enough, it can lead to speaker failure (coil shorting or mechanically wedging in the magnetic gap.) Aluminum formers also create eddy-currents which lower the mechanical Q (Qms) and create additional heat, neither of which is a trait we were looking for in the W7 design. The modest power-handling advantage of an aluminum former pales in comparison to its practical incompatibility with the W7 design.

 

When a speaker is asked to handle the kind of power that a W7 is capable of handling, removing heat from the voice coil and motor parts becomes a big challenge, but one that has to be addressed in order to ensure reliability and sound quality. The vast majority of the power entering a woofer is converted directly to heat. The reason for this is that the speaker is a highly inefficient device. You may have heard that a typical amplifier is 50% efficient at rated power (this means that half of the power entering the amp is converted to heat). A typical, small-box woofer's efficiency (W7 included) runs at well under 1%, meaning that over 99% of the power you put into it becomes heat very quickly.