The bottom line is that it comes down to "balance". Everything is relative, and often comes down to compromises in the room, the equipment, the seating possition(s), and possible setup options. To say that you need to put your speakers in one location, because someone believes that "one particular" mixing studio has their system setup with the speakers at "waist high", or whatever, is assuming alot, and not really practical mostly. (I mean, you go to a large movie theater, where you know that the speaker system is going to be WAY WAY WAY UP HIGH, in relation to the seating audience, and you gotta know it's not usually going to end up that way in someone's home setup often! And, even then it's a compromise between the height you might want to listen music at, which may or may not be lower. Also, where's the screen height?--etc, etc.
Again, it always comes down to BALANCE!
I've heard people here on the forums say they think speakers
should be placed this far apart, and that high off the ground, or next to your side, 6ft up, or in the corners, or just behind your head for the side/rears, or having on directly behind your head for a rear speaker, or even having
multiple subs placed 1/2 way between the wall lengths, for bass mode cancelation. Then some say subs in corners, or just upfront, or just behind your chair, or dipoles vs. monopoles,...yada, yada, yada!!
My many many years of experience with all of this is this--It gets down to balance, and it's all a compromise! There is no perfect solution--just choices, options, and better solutions, given certain variables.
I will say however that there are certain guidelines to adhere to that will consistently yeild better results, IMO. But again, it depends. For instance, matching speakers across the front, at the very very least! Yes, ideally I want speakers arrayed the same, at same height. And usually I want speakers up higher for movie applications, as it produces a soundstage that gives more presence, and grandure to the scale! Kinda "larger than life" experience. But it depends. Same with speaker spacing and width of placement, in relation to the seating possition(s). How far apart? Well it depends on varaibles such as screen width/perspective, a balance of solidity of immaging you want, with 3 speakers playing up front, vs. two for stereo music, plus how much envelopement for multi-channel sound for how big of an audience, etc.
My main concern, first is however, is that the speakers all need to couple well in the room, in relation to the seating possition(s) for FLAT RESPONSE, and solid dynamic range. (also, critical coupling at the crossover to sub). This is THE SINGLE MOST IGNORED AREA of consideration when people place speakers!!! They put the speakers where THEY THINK they should go, irregardless of how well the speaker actually sounds in any particualar location, by itself!!!!!
I mean, what good is it to put a speaker, or center speaker, or whatever, where it's going to sound crapy? It's just going to pull the overall integrity of the system down, if it doesn't sound good where it is to begin with!
As for two center channel speakers, I'd say most would need to know all the variables, and to know what they're doing. You can easily cause more problems than you solve, by using two speakers in the center, if you're not aware of the variants in the room, seating, speaker design, comb-filtering, level matching, phase issues, etc, etc. For most I'd say stick with one well placed center speaker, that's balanced well for good response (yes, try to keep them on the same relative plane as L/R speakers, and arranged the same way, if you can), and anchored to the screen. But you do need to know what you're doing. And that takes experience, based on all the variables. Which you likely don't know.
Ah yes, there's no replacement for experience. If you want something done right, you go to the professionals! Otherwise, you get what you pay for (or don't pay for).
Nothing in "life's lessons" has changed in the last few thousand years. That goes with knowing how to set up an audio system for performance, either. good luck
