40 years ago I had I. M. Fried Model M (derivatives of the famous "coffin" Model H) 6 cubic foot passive woofer cabinets that were capable of 114 dB at 17 Hz. More powerful than any room I'd ever afford, but with 20 wpc sounded magnificent in a 20,000 cubic foot chapel. They used a tri-folded transmission line design that Fried was a genius at developing. Not only powerful but dynamic and musical.