Used to be a Tannoy Dealer in the 70's; sold a few of the 15" CoAxials. Very efficient, big SPL ability, and yes, "coherent". A great "Turn It Up" Rock speaker that never came back for repair despite duty that most speaker manufacturers would consider abuse, the Tannoy's considered "Business As Usual".
We sold way more Klipsch LaScalas to that type of customer, and we were JBL Pro dealers (not the consumer range, which is a different line) for sound reinforcement customers, but Sound Quality (SQ) wise the Tannoys had an edge, although we also sold UREI, and their Time Aligned CoAx Studio Monitors were decent sounding units properly installed in a studio.
All of the above sounded better than the Altecs (604 CoAx) by a wide margin. In fact the Altecs were marginal in every respect; not as durable either. We ended up dropping that line after trying it for about 18 months, even though Altec had attractive margins in comparison to most brands, the Sound Quality just wasn't there (beautiful Oak cabinetry, but that was the best feature).
The market has changed, of course, since then, somewhat away from the high SPL ability to a SQ emphasis, but CoAxial is a very sound construction with genuine sonic benefits. In particular they can have advantages in Phase (or "time") alignment.
