I am fascinated by Uncle Eric and Nic Rhodes advocacy of 'servo' sub-woofers. Various strategies were tried several years ago both in professional monitor speakers and hi-fi designs. Phillips were particularly keen on the idea, if I remember correctly. In fact the last ones I saw remaindered a couple of years ago were Marantz. After the initial enthusiasm all these designs were ultimately seen as flawed by the majority of critics which is presumably why they fell out of favour. So my questions are these: Is there some new development which has suddenly made this technology truly viable? Or is it simply that the restricted frequency range of a sub makes the problem less intractable? If the former, it would be interesting to hear about it and the likelyhood of seeing new full range designs on the market. As a result of Uncle Eric's enthusiasm, I shall make sure I hear some examples of the subs soon.