CD, DVD, and SACD transport mechanisms use motional feedback systems called servos to keep their laser beams focused properly. Without the benefit of this technology, optical disc readers wouldn’t be possible.
Another type of motional feedback system is used to control woofers. In this setup, feedback traces the woofer’s travel and compares it with the incoming signal because the two are never the same. A balancing circuit uses the correction information to straighten things out and the results can be amazing. Distortion is lowered by an easy magnitude. And overhang, the propensity of the heavy driver to exceed its positional charter, is nearly eliminated. Servo control of woofers also improves transient response, so formerly sluggish woofers match the speed of even the quickest electrostatic or planar speakers.
In fact, there’s every reason to engage servo technology with any internally amplified low-frequency driver—which makes it curious that there are so few to choose from.
I wonder why that is? Too technically difficult? A lack of interest?
If you’d like to learn more about servo controlled drivers…
I’ve put together a short video on the subject of servo controlled drivers. You can view the video here.