Wow, all that sarcasm over the addition of just 2 surround speakers? Does going from 5 speakers to 7 really offend your sensibilities that much? I can’t speak for others, but there were three reasons I went beyond a 5.1-speaker set-up: more precise localization, better envelopment, and greater stability in the surround field. Follow:

Using four surround speakers allows you to have sounds clearly localized at your sides or behind you (or both). You don’t get this sort of distinct imaging when using only two surrounds; the best you can hope for is a good compromise between side and rear sound placement. Also, processing like PLIIx isn’t necessary to notice this difference; simple EX decoding and a good soundtrack will let you hear surround imaging to your left side, to your right side, behind you, and everywhere in between.

Why would you want rear vs side imaging in the surround field? Because some surround content (e.g., spatial, ambient effects) usually sound better coming from your sides while other surround effects (e.g., front to back flyovers) sound more realistic when they end up behind you. This sort of localization is not difficult to achieve when you have speakers at your sides and speakers behind you. So why compromise?

Along with the improvement in imaging comes better envelopment in the surround field. Four speakers can, literally, surround you better than two speakers. This allows for a much nicer sense of ambience without any holes in the surround field. Also, four speakers firing simultaneously are capable of creating excellent diffusion in the surround field without having to resort to diffuse speaker designs (like dipoles). It’s nice to have precise imaging and enveloping diffusion simultaneously.

Finally, the best part about a 7.1-speaker set-up is the greater stability you get in the surround field. For example: no matter where you sit on you couch, sounds intended to come from behind you will always appear to come from there; not some side-ish, rear-ish direction. No magic involved, just a pair of speakers physically placed behind you (makes it hard for those sounds to come from any other direction). Again, this is difficult (if not impossible) to do with only two surround speakers, where you’re relying much more on phantom imaging.

BTW, 7.1 isn’t some new concept. If you look at companies who have a history of specializing in leading edge surround processing (Fosgate, Meridian, Lexicon) you’ll notice one thing in common: they’ve all built their technologies around a 7 speaker configuration. That’s some coincidence. All that’s happening now is that the rest of the industry is finally catching up.

Best,
Sanjay