And the Intersonics use rotary motors rather than linear voice coils to move fairly conventional cones with their suspension limited travel. However this can be scaled to any ridiculous distance nowadays. There are plenty drivers that produce over +- 2cm excursion esp in the US

I agree with your dad, a compressor + pump, and a +ve and -ve reservoir tank and some fast valve would produce bass down to DC.

This one will always be a good but daft idea since it has a DC offset [ie a breeze..] and fan noise - which would get worse if you put a safety guard on it.

I like:

'They calculated that it would take ten 18" subwoofers to produce this level of sound'

or just 1 Intersonics Contrabass, Aura 18" or Adire Tumult, or loads of other OTT drivers..

Pretty small though, for what it achieves.