Quote from Tom from a Q&A on Audio Express:
Sonically, Synergy horn’s success is simple but one has to hear it. It is a way to combine more than one driver in more than one frequency range into a single, constant directivity horn with the appropriate crossover. The outcome literally appears to be, measures like, and sounds like a single crossover-less driver.
That sounds simple, but it is surprisingly hard to do. An example of its effect is that you can walk up to the speaker, move around, literally even put your head deep into the horn mouth of a three-way Synergy horn, and never hear any clue there is more than one driver. Many of them can even reproduce a square wave over a broad band, even with a passive crossover. In large-scale sound, this sounds dramatically different than the concert-style arrays.