I don't think a cyclone would be much use for a horn box due to the fact it is essentially a modified fan. The pressures generated by this would not be sufficient to drive the horn - the extra resistance would effectively cause the air just to stay put. Cone style transducers are most suited to horns.
I think the servo motor ideas still have mileage in them, the main problem holding us back on SPL is the linear motor design. There are ways of course of making a hell of alot more SPL for the same size box by abandoning the linear motor. However at the moment, it has the upper hand because of relatively low cost and low distortion.
