More than one way

January 26, 2020
 by Paul McGowan

While I am not into skinning cats, there's always more than one way to get where you need to go. Take woofers as an example.

Years ago, Arnie Nudell, Bascom King and I relied upon an active feedback system to lower woofer distortion, equalize performance within the box, and improve bass response in the speakers we made for Genesis Technologies. The technique of active feedback around a woofer is called a servo system, a name coined in the 70s when Arnie first launched the Infinity Servo Statik 1.

Servo technology is great, but it is not without limitations. Nothing we engineer is. The problem we ran into was a reduction in the apparent slam factor. Servo control on and distortion got lower, but the slam factor seemed weaker. At the time, the benefits of lower distortion and flatter frequency response in a given box outweighed the reduction of slam.

Move forward to today and we find ourselves experimenting with another path: designing a woofer that already outperforms the best we achieved with a servo. In other words, eliminating the need for the fix-it in the first place—like designing a zero feedback audio circuit.

Getting there is far more difficult than implementing a servo system. In order to outperform an active feedback arrangement, our speaker designer, Chris Brunhaver had to pull out all the stops.

In order to make the woofer more dynamic, he went to what's known as a split gap woofer design for linear BL versus excursion (increased slam factor). Traditionally, the motor force drops with excursion in either direction, something you don’t want and something the split gap woofer design solves. Next, Chris optimized the compliance (ability to move) versus excursion (the distance the cone travels) using a custom tooled surround, suspension, and double mirror-imaged spider assembly (the spider is what holds the rear of the cone in place). Lastly, inductance (versus excursion and current) is linearized through the use of a Faraday ring in the split inside the magnetic gap, and symmetrical shorting rings. This both lowers inductance (increasing apparent speed and bandwidth), reduces AC harmonic distortion, DC offset, and magnetic rectification.

Lots of engineering talk, but bottom line, it's likely going to be better. Stay tuned.

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