The things we do to extend our playing time or achieve stereo!
the Gaumont auxetophone requires a large room and has entertained audiences of 4000 when used with 110v supply but was clearly a DD model
'Surprisingly, it's important. Very important, in its specialised field. We probably wouldn't have got to the moon without it. Compressed air modulated by valves is used to generate enormous sound levels in test chambers'
Im not sure where the sweet spot was though
Sadly and here is the sting in the tail I found this whilst assisting Ken C in the sale of his Atco so the details of this magnificent item will require a quick visit to his thread ...... sigh