The 12 Shivas Dancing is from the above link to other
sonotube links. I have simply no way of building anything
into the floor, but there is an Open Baffle site that shows
a number of these projects.

And in here, you may be able to do a search for
The World's Biggest Speaker... a project made in Italy
where a concrete form as big as a basement makes the basshorn.

Makes you all tingly, doesn't it? ;-)

Here is another sonotube which has been in the TL forum...

• Sonotube subs with Shiva