Just finished building the "double" ART Array I post about a few weeks ago. Tweeter spacing is 4", but they sound awesome. The guy I built them for listens to 80's hits and techno music, and there is not any noticable problems with the double tweeter. Before I cut the baffles, we tested the tweeters just holding them up in front. In his room with the speakers placed as they are, there really did not seem to be a problem with tweeter spacing until they are about 8" apart. These are being driven by a Carver TFM-55 (380 x 2 RMS) and the sub is a Mach5Audio IXL-18 in 13 ft^3 tuned to 18 Hz with the Dayton 1000 watt chassis mount sub amp. This guy wanted LOUD, and we definitely achieved his goal. . .