One of the hallmarks of THIEL loudspeakers has been the incorporation of unique technology in our all THIEL-designed drive units (drive units are the individual woofers, midranges, and tweeters that make up a complete loudspeaker system).

There are many aspects of driver design that Jim Thiel has addressed over the years to optimize performance, but perhaps none as fundamental or important to the final sound as the incorporation of short-coil/long gap technology.

The driver’s voice coil, which is attached to the diaphragm, is positioned inside a magnetic airspace (called a gap) created by the fixed structure of the driver’s motor system. This fixed structure, comprised of a magnet, steel top and back plates, and a center pole piece, creates a magnetic field around the voice coil. When power from an amplifier is applied to the voice coil, motion of the diaphragm/voice coil assembly is generated due to the interaction of the voice coil’s electrical current with the magnetic field. This motion of the driver’s moving system is what creates the sound we hear.

A typical driver will have a magnetic airspace for the coil that is somewhat shorter than the voice coil itself (a short gap). By allowing a longer voice coil to overhang a magnetic airspace that is shorter than the voice coil, the voice coil can move a given distance and still have some portion of itself inside the magnetic airspace. This avoids excessive distortion while the coil is moving; however the results are not fully satisfactory because magnetic leakage exists both in front of and behind the magnetic airspace. Depending upon the position of the coil within the air space as it moves, interaction with this leakage magnetic field produces significant distortion (usually up to about 20% before the coil leaves the air space).

Jim Thiel’s solution has been to develop the short coil/long gap technology. In this system, the thick, multi-layered voice coil is as short as it can possibly be in length. The magnetic air space of the gap is made much longer than the coil. When demanding high power conditions are applied to the voice coil, it is able to move very far in either direction without any of the coil ever leaving the full strength of the magnetic air space or interacting with the magnetic leakage.

This approach requires magnets and magnet-system parts that are several times as large and expensive as those found in conventional driver systems, but the startling results are a ten times (order of magnitude) reduction in driver distortion, even under the most demanding of conditions. Thiel’s short coil/long gap driver technology is heard by the listener as cleaner, clearer sound reproduction that does not disappoint for ease, naturalness and effortlessness.