I played bass through one of those 30" EVs until the patch job that someone had done to secure the dust cover/dome/voice coil pulled out of the center of the cone. Seems they had used hot glue which the cone wasn't to crazy about. I asked the guy that does my reconing about that speaker and he said it was "squeaky ice chest foam".
It sure was impressive to look at. We always could hear people in the audience say "Look at that speaker!"
The cabinet was huge and a real bugger to move.
That was in about 1970 I think