The Genesis servo-controlled bass system is a pretty easy one to understand. A little accelerometer is mounted on the voice-coil of the woofer. A circuit on the preamplifier/crossover senses the signal generated by the accelerometer and compares it to the input signal. A differential circuit then generates the difference and this is injected back into the amplification system. In effect, it is a negative feedback loop that goes all the way from the woofer to the input of the amplifier.
There are many debates to say that feedback is bad, but correctly applied, feedback fixes a host of problems. For example, a woofer has weight - and hence inertia and momentum. The servo-system is a "brute force" approach - when the servo-circuit senses that due to inertia the woofer cone is not accelerating as fast as it should be to track the incoming signal, it pushes more power at the woofer. And, if it senses that due to momentum the woofer is overshooting the signal, it pulls the woofer back. The effect is "infinite" damping.
What has all this got to do with the Servo-bass cable?
As the accelerometer is in the woofer, and the amplifier is outboard, the servo-bass cable is inside the feedback loop, and it is the interface for both the woofer driving circuit as well as the accelerometer sensing circuit.
The original Genesis Technologies servo-bass cable used two twisted pairs of 14awg wire for the two different signals. Since the accelerometer signal is very low current, very low voltage (almost like a phono cartridge), and the woofer signal is high current high voltage, magnetic coupling between the two twisted pairs created crosstalk that contaminated the accelerometer signal. Also, the old servo-feedback circuit oscillated when the cable was too short. 10m of 14awg speaker cable to run multiple 12" or 8" woofers was too skinny a cable.
The next version was developed by Audioquest - it was a bit better with two 12awg twisted pairs. However, the magnetic coupling between the two signals was still there, and they still needed 10m of cable to reduce the risk of oscillation in the servo system between the woofer and the amplifier.
Enter Genesis Advanced Technologies. We looked at the servo-bass cable from first principles.
There were two different signals that the cable had to carry - the woofer driving signal from the amplifier to the woofer, and the feedback signal going back to the amplifier. Obviously both signals had to be treated differently.
Since the woofer signal is a high current signal (necessary to drive up to four 8" woofers per channel), we used two 12awg copper conductors for the current. Since the signal would be purely in the bass, and any high frequencies would be noise, we used soft polyurethane as a jacket (soft and high capacitance). The soft polyurethane also help to control any resonance or vibration in the cable.
To carry the low-voltage low-current feedback signal back, we used an 18awg interconnect cable. Again, since the signal is only in the bass, high inductance is a benefit as high frequencies can be filtered by the cable.
To reduce the magnetic coupling between the two signals, we put a shield between the two. But what worked even better to reduce magnetic coupling was to have opposite twists on the inside feedback signal and the outside woofer signal. Geometry is hence important, and we needed spacers to hold everything together.
The result - better bass and shorter cables! No more need for 10m cables to prevent oscillation.