I have been thinking about how horn drivers were once available as wide range or approximately full range speakers. Whether it be Western Electric's model 555 with the small aluminum diaphragm, or RCA's model 1428 with it's big 5 inch Bakelite diaphragm. Today we can not buy compression drivers which play bass.

Can someone tell me how a modern driver might be modified to play several octaves lower than it currently does?