Some active subwoofers are also servo controlled, using a feedback mechanism which generates a signal based on the movement of the cone. The signal is used to correct for any deviations from the motion intended. Several manufacturers make servo subwoofer systems, usually accelerometer-based. The advantage of servo subwoofers is reduced distortion. The primary disadvantages are cost and complexity. A successfully implemented servo system addresses the limitations of conventional subwoofers:
- mechanical non-linearities
- thermal non-linearities
- magnetic non-linearities