So many designs shine with proper implementation. As you know, Eric, for a D'Appolito, optimizing the MTM vertical off-axis response and achieving the best mid-mid comb filtering response are givens. Here's why I like MTM - in theory: I prefer cone midrange drivers over cone midbass drivers, but I also want as much midrange cone surface area as I can reasonably get for "scale" (for lack of a better descriptor). Nice 6-8 inch dedicated midrange drivers exist, but beaming at crossover frequency and breakup at top end come into play much more than with most 4-5 inch mids. My "one of" MTMWW loudspeakers use a pair of 4 inch mids, with a 200 cm2 total surface area. I use an older "non cell" 1.2 inch Accuton tweeter between them, in part for the very short 82mm per side square face plate (sound nice, too). The larger diameter tweeter lets me cross at 2kHz, well below both midrange driver beaming and significant combing frequencies. The 1.2 inch may have a bit less sparkle at the very top compared to its 3/4 inch brother, but my aging ears probably couldn't tell. This particular MTM has the qualities you listed, and the midrange "presence" with the smaller cones makes a difference I believe. I haven't heard a WMTMW, but smaller woofers should generally sound better in upper bass/low midrange and still move as much air as a somewhat larger single driver. My previous speakers had a 15 inch woofer, and I prefer the 9 inch bottom WW woofers I now have.
Unsound: Your comments absolutely apply. Driver synergy, crossover design, enclosure materials/construction are as/more important.
Unsound: Your comments absolutely apply. Driver synergy, crossover design, enclosure materials/construction are as/more important.