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...and early 70s...I just read an interview with ATC's engineers and they said when the co. was founded ('74), they tried to blend the high dynamic-range of U.S speakers with the 'better fidelity' of the U.K. Even saying the U.S. "often used horns".
I know about Klipsch and Altec, but I thought ESLs held the day -Quad, Janzen, KLH, and by the late 60s, Infinity. It appears Acoustat, Beveridge and Dayton-Wright came out in the 70s.
Maybe ESLs took longer than I thought, even in perfectionist circles !
Edits: 06/15/17Follow Ups: