Technology & Engineering

Extended Linear Motion Voice Coil

Quick anatomy lesson: A voice coil is a piston inside the motor of your speaker. It sits in an electromagnetic field generated by the signal your speaker receives from your source (your receiver). As the magnetic field fluctuates, the voice coil reacts by moving back and forth in a pre-determined space, suspended within and controlled by, the magnetic field. The driver, attached to the voice coil, vibrates in accordance and reproduces sound.

The faster the voice coil moves, the fewer impediments to its movement, and the farther its overall length of movement is, all determine how quickly and energy-efficiently your speaker reproduces the sound of the signal.

The Polk Extended Linear Motion Voice Coil is based on a design that efficiently increases a voice coil’s freedom of movement (even with a shorter coil length) and boosts its transient response over a wider bandwidth. As if that’s not enough, this ELM design is shown to reduce midrange distortion by almost 30%.

The secret of the design is tricking a short voice coil into thinking it’s a longer, larger voice coil. Notches cut into the motor structure change the structure of the space in which the voice coil moves. As the shorter, lighter coil moves over the notches, the energy is distributed in a far more efficient way. The coil moves faster in a shorter space, yet produces nearly the same performance specs as a longer voice coil in a larger space. 

Using this incredibly efficient design, Polk engineers have been able to cram the bold, dynamic performance characteristics of full-size loudspeakers into enclosures with severe size limitations. You’ll find ELM Voice Coils in the shallow-depth Vanishing Series of built-in speakers, and in the compact high performance RM and Blackstone loudspeakers.

With the ELM Voice Coils, these speakers don’t sacrifice audiophile efficiency and high performance standards for the conveniences of built-in style or compact size.

This article was last modified on Jul 10, 2012

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