The Servo-Controlled Advantage
In order to convey the bass frequencies accurately, a woofer has to move extremely forcefully in the air load of the room. This necessitates a large, strong (and therefore heavy) woofer cone.
When you have a high-impact, low-bass signal that starts and stops suddenly (for example a tympani), the inertia of the woofer cone makes it slow to start moving, and then after it is moving, its momentum makes it continue to move after the signal has stopped. Most loudspeakers rely on the amplifier to supply sufficient power to make the woofer cone start moving, and relies on the amplifiers damping factor to stop the cone after the signal stops. However, this can not totally fix the problem. The sonic result is overhang, bloat, lack of tautness and definition, and a blurring of dynamic impact.
The solution for this is the Genesis Servo-Controlled Bass System. The concept is an easy one to understand. An accelerometer mounted to the woofer voice-coil is used to continuously monitor the motion of the woofer cone. A comparison circuit instantly compares the motion to the input signal, identifies any deviation, and instantaneously applies a corrective signal to compensate for any deviation between the input and the woofer - correcting for both the inertia and the inherent non-linearity of the woofer.
With the servo system, the circuit senses that the woofer is not moving as fast as it should, and it applies more current to make it move faster. When the signal stops, it detects that the woofer continues to move when it shouldn't be and applies a counter-signal to stop the woofer faster and more effectively than an open loop woofer could possibly respond.
Thus, the servo-drive reduces distortion and improves transient response by making the woofer appear to be massless. Typical non-servo woofer systems have distortion levels that exceed 10% at even moderate levels. The Genesis servo bass system reduces this distortion to below one percent at almost any output level. The system also drives the woofer to constant acceleration, which makes the frequency response of the woofer anechoically flat to the lowest frequencies.
Very few loudspeakers use servo drives, either because most designers think that it is too difficult to design, too expensive, or because of the extraordinary demands a servo system makes on the amplifier and the transducer. It demands an extremely powerful and current-capable amplifier, and a tremendously strong transducer.
The system in totality is also not easy to design. Arnie Nudell and John Ulrick first introduced it in the legendary Infinity Servo Statik One in 1968. The technology has been constantly refined by Genesis, resulting in a reliable system that delivers "floorshakingly-musical bass".