Nah, you can't easily dynamically downmix surround sound audio to stereo. In the main mix, the dialog mostly comes through the center channel, and the left and right surround sound speakers are used for sound effects. If you simply split the center channel to left and right without massively boosting the volume of the center channel first, you're going to have stupidly loud sound effects (from the L/R surround sound speakers) and the dialogue will sound like whispers. If you're playing the movie from a PC, you can boost the center channel audio with software, but sometimes (e.g. when a character is off-screen) dialogue will come from the left or right channels and you won't be able to clearly hear them.
If you've got a stereo speaker setup, there's no good solution unless you can get your hands on the actual official stereo mix (some streaming services let you select this), but even the official stereo mix is an afterthought cobbled together by some overworked and underpaid audio engineer: the primary mix is absolutely the theatrical mix with all the surround sound channels, then everything is downmixed progressively from there.
I've had no problems with downmixed surround on stereo speakers. Never had a problem with dialogue, not once. And I've watched basically every notable English-language film that's come out in my lifetime.
I didn't say anything about a centre speaker, though. A centre speaker is useful when you have a large screen and people will be sitting outside of the sweet spot. You don't have to be far outside the sweet spot before you lose the ghost centre channel. But you can still get really far without a centre channel and it's much easier because the ideal position is behind the screen which is hard to achieve (requires an acoustically transparent projector screen). The ghost centre channel is always behind the screen, though. Some AVRs even include an option to "lift" the centre channel by mixing it into the L/R to account for the common suboptimal below-screen positioning of the centre speaker. I've never tried it, though.
Nobody has ever heard my stereo set ups and commented on lack of surround speakers. And when I did have surround speakers nobody ever commented on them. Nobody ever couldn't hear the dialogue. They were always impressed with the bass and dynamic range.
For me, the diminishing returns are something like this (specifically for film soundtracks):
- 60%: Good stereo speakers (preferably full-range, down to 60Hz),
- 80%: Quiet environment and ability to listen with full dynamic range at close to reference SPLs (ie. no kids, no neighbours annoying you or you annoying them),
- 90%: Good subwoofer to add the actual sub-bass material (down to 20Hz),
- 99%: Good LCR set up (ie. centre matched to the L/R speakers),
Leaving 1% for anything extra like surrounds etc. It's just really silly to add surrounds before getting the huge gains above.
> Leaving 1% for anything extra like surrounds etc. It's just really silly to add surrounds before getting the huge gains above.
This advice would save so much headache for so many nerds. The juice is simply not worth the squeeze unless that whole checklist is already satisfied and you are still not blown away.
