Back a few decades, I remember a slickly published 'song-and-dance' about a loudspeaker driver that had two additional DC coils (electromagnets) placed either side of the voice coil. The idea was that as the cone extended, the 'electromagnetic' force of the additional electromagnets would increase/assist the travel of the cone, to counter the air compression in the cabinet (sealed).
At the time, I thought that this was revolutionary (and wished that I'd though of that idea - such a simple, elegant idea).
The claim was that they would make a small, sealed, loudspeaker significantly more efficient at the lower frequencies. However, the 'company' disappeared as quickly as they appeared.
Does anyone remember this? Did they actually ever work? My feeling is that they probably failed - badly - in practice - hence, it's never been seen or mentioned since...
