To my understanding Dahlquist was the first with that type of speaker design. I owned them many moons ago!
Dahlquist DQ‑10
One should always be wary of pronouncing “firsts,” but, appearing in the early seventies, Jon Dahlquist’s DQ‑10 was to my knowledge the first dynamic speaker to employ multiple drivers in an open-baffle configuration (except the acoustic‑suspension woofer, which was enclosed) staggered for proper time‑alignment and phase coherence, in an attempt to realize the openness and freedom from boxiness that Dahlquist prized in his beloved Quad ESL-57s—with the added advantages of deeper bass and dynamic extension well beyond the Quad. (The physical resemblance to the Quad was both mandated by the design and an intentional homage.) Far from flawless (including conceptually), the DQ-10 was nevertheless a ground-breaking design that preceded dozens of subsequent speakers (perhaps most prominent among them models from KEF, B&W, Spica, Thiel, Vandersteen, and Wilson) continuing up to the present day. Few large, full-range dynamic speakers before or for some time afterward equaled its openness. Paul Seydor
