Hi jkohn and all,
Just a few thoughts and facts here: The final sound mix for a Dolby Digital or Dolby Surround movie is done in a mixing theater--an almost full-size movie theater with a big screen, lines of surround speakers down each side wall (plus a couple at the rear) and a big mixing console smack in the middle of the theater. I've been present for a final mix in the Alfred Hitchcock theater in L.A. at Universal. The point is that the movie sound is mixed for envelopment, as well as for directional effects. Like you say, direct radiators work well in big domestic rooms and in movie theaters, but in smaller rooms and typical living rooms, multipolar radiators are usually more effective at creating envelopment, are less fussy to position to achieve the latter effects, and, in my experience, give up nothing in terms of precise directional cues when needed.
Certainly direct radiators are the only choice for home theater main speakers, but bipolars have their place for stereo music reproduction. The stereo illusion is intrinsically flawed because in stereo music reproduction, the direct sounds AND the ambient sounds are thrown at you from the front, which is not the way it happens in real life. That's why bipolars can be highly effective (in stereo) for recreating a more realistic mix of direct and ambient information, albeit at the expense of precise imaging.
What I have discovered using multipolar radiators at the sides for DVD-A and Dolby Digital/dts music is that the "sweet spot" is remarkably generous compared to using direct radiators as surrounds. In demos of DVD-A and SACD, as well as other experiments in which I participated using full-range direct radiating speakers, the sweet spot was incredibly critical. Moving the listening chair even a foot or so made the illusion collapse to the speaker nearest the listening position.
I'd be interested to hear about others' experience with multichannel music and bipole/dipole/quadpole surrounds vs. direct radiating surrounds.
Regards,
