Servo controlled speakers and subwoofers

A servo involves a sensor on the controlled device (in our case a small accelerometer on the woofer cone) which measures movement of the cone. With a non-servo system the power amp puts out a voltage according to the input signal. The voltage is applied to the driver, but how the cone moves depends on the driver characteristics, and no driver is perfect. With a servo system, if the driver fails to move exactly in accordance with the input signal the error is measured, and the power amp output is modified to correct it.

Beemer is exactly correct, and thus unfortunatley has to reveal he's over 60? if he remembers the IRD Beta problems. I even remember the Infinity Servo-Static! which had similar problems, but was a 'killer' product in its time!

Today, the long control cord problem has been solved by simply including a dedicated SS amp within the sub. Personally, I wouldn't buy a sub without a servo (accelerometer) it solves so many problems, though not a substitute for cheap construction/drivers.

...thanks for your explanations Eldartford and Beemer.

Why are the amplifiers that come with the 4 chassis systems so small in comparison to other amps that have to drive big speakers? The Genesis 201 bass columns have eight 8" woofers per column and both are run by one amp that doesn't seem all that big. Does the accelerometer lessen the power requirements of an amplifier?

Nsgarch, what are those colums with 5 woofers per side in your system? Do you use a servo to drive those giants?

Mitch, actually, I don't use those SW-800s (Kinergetics) anymore. I use a single Martin Logan Depth and it's great (it does use a servo, BTW) Sorry about the outdated pic. That's one of my spring projects.

Most on-board sub amps are I believe Class D "switching" amps. They're designed to only drive the lowest couple of octaves. I'm not clear on why, but they don't require big power supply transformers or storage capacitors.

You still need a "regular" Class A or A-B amp for the mid/highs, although there are now some alternates to those as well.