This thread reminds me of one of the first high-end speakers I ever heard, the Von Schweikert UniField Model Three. They were described as an augmented one-way speaker. It used a Fostex FX 120 to cover 100Hz to 8kHz. It had a Fountek ribbon tweeter covering up to a claimed 50kHz and used a 7" SEAS magnesium woofer in a transmission line to cover the bottom end. It was a sweet sounding speaker.
Martin