Wayne and curegeorg,

Yamaha uses servo control on many (if not all) of its subs.

I've used a Yamaha YST-SW/80 in my dining room in a three piece stereo configuration for years.

Within its design limits, and at all reasonable listening levels, its a great little inexpensive sub - as are others in the current product line.

I don't expect it to compete with my Velodynes or B&W subs, nor should I.

Jeff Mackwood