Double Coil Speaker

I skimmed this, expecting it to be another useless re-invention, but it actually contains an idea I haven't seen before: When a speaker is driven hard enough that part of the voice coil leaves the magnetic gap, that part of the coil ceases to contribute force, so it doesn't need to be energized. This means you can get away with a smaller magnet for a given amount of linear excursion. I don't think this would be practical in reality though, since surely the extra expense of a second amplifier will outweight the saving of a smaller magnet.