Fun? Sure. It is indeed fun to play with big speakers.

Direct-radiating bass reproduction is all about displacement, and the area of the piston (cone) is certainly a factor of that. More tends to be... well, more.

And this mysterious speaker (which there seems to be no color photos of, despite the 1981 date) has a radiating area of perhaps about 2 square meters.

That's around the same as qty. 18 of 18" woofers.

It's easy to find collections of way, way more than that. People even charge money to hear them; they're on the ground between the stage and the crowd barrier at any big rock show. :)

The japanese version of the article linked in another comment has a color photo (which appears to be a magazine scan) https://audio-heritage.jp/DIATONE/diatonesp/d-160(1).jpg