Disgression 1: 5.2 Channels

 

The Main 5.2 Channels

The main speakers, LS, LF, RF, and RS, are equidistant from the listener and positioned at 60 degree separations. LFand RF are bisected by C, which can be a slightly smaller speaker from thesame family of speakers, since the bass frequencies are often routed tothe bigger speakers. But that point becomes moot when you have subwoofers.In this case I made a trade off for two smaller subwoofers instead of onelarger one. With careful A/B comparisons I learned that the bass wasnearly the same when the two smaller units were working together as a teamas with the single larger unit. But there was, contrary to what I hadread, a small amount of additional directionality present with the twosubwoofs compared to one. Yes, on steady tones and those with slowerattacks you heard little difference. But on transient waves, hard attacks, dynamically changing signals, you began to perceive a small amount ofstereo effect with the two, SWL and SWR, asshown above. I went with that arrangement, you may prefer the other choice, while the cost is similar.

Modified Front Speaker Placement-- 5.2 Channels

I've seen setups more like the one above. What's differentfrom the view just above is that the LF and RF speakers have been rotated not to be so toe-in as before, and the centerspeaker has been brought slightly closer in, more as many three channel monitors are located in mixing theaters and even small home theaters. It'snot a big change, and is one we'll pick up again below. If the listeningroom is not as deep as it is wide, these mild repositionings will beappreciated. The sound will not be greatly affected at all, unless you cancompare the two setups one immediately after the other. Then you may heara slight reduction of the in between imaging. But it won't be any worsethan when you listen to two-channel stereo from slightly off the exactcenter spot. It's not going to destroy the surround sound field, but I bring it up as it has become somewhat common.

Maximum Side/Rear Separation Setup-- 5.2 Channels

Here you see a fairly common variation that many studios are happy with. The front speakers are as they appeared in the previouslayout, less toe-in, center speaker more inline with the LF and RFspeakers. I've also shown the room with stereo subwoofers, as my room hasthem, in the original views. But here we've made a slightly larger trade off. The two side speakers, LS and RS, have been moved rearwards. Inthis case we've not gone very far, they are both a mere 5 degreesrearwards of the position above. If you try this for yourselves I thinkyou'll discover not much change. The side channels still sound reasonablyto the sides (you're losing a little of the ability to position sounds tothe exact sides -- a compromise). But you'll find that the effects thatyou want to locate rearwards remain rearwards a little better if you shiftyour head about while working. Once you stop moving either setup is fine,but when you move your chair back from the console in this new setup theside/rear sounds will stay more rearward than before, at the price ofextreme side positionings.

 We're splitting hairs here,I admit it. Still, you don't want to go too far with this variation. Morethan 10-12 degrees rearward bias on LS and RS, and you create the same oldproblems, losing more than you gain, don't fool yourself. Try it out inseveral rooms using different program material with lots of side and rearactivity. There are convincingarguments to be made that this might be a pretty decent compromise to makein many studios, and in many theaters and homes. You can be fooled by thevisual impression, thinking that the first variation has only front andside loci, the second adding a little rear. Um, sorry not true. The firstsetup can create a completely convincing wrap-around effect, which willonly vanish if someone is moving greatly, or decides to sit at a steepangle to the room, sidesaddle. Then the sound will remain confined to theone hemisphere. People sit sideways all the time with the foolish fourcorner positionings described above. Watch them squirm and twist about, trying to figure out: "speaker, speaker, who's got the sound?" With an arcof sound they don't do that nearly as much. And you won't want to, either.

5.1Surround Sound for Music

Now this is the monitoring arrangement I hope each of you has or will have, to check out your surround mixes. Note that this time we have a single subwoofer (position not critical), as most setups are arranged that way. You lose only alittle compared with stereo subwoofs, since most low bass is omnidirectional (but not all -- hard attack bass sounds do establish small directional clues...). This is a variation of our initial plan. The LF andRF speakers have been rotated slightly for less "toe-in." That's becauseyou'll probably want to allow several people in the room to hear what'sgoing on, and many listeners don't like to have their stereo speakers too angled in these cases. There are good arguments that suggest that moretoe-in has notable benefits, but this is a topic for another discussion.Similarly, the center speaker is moved slightly closer to the listener, as it will be so in most movie theaters, home theaters, and professionalstudios. There is equipment that can correct forsuch differing distances by adding a 1-4 ms. delay to the too-close speaker(s). Your preference still ought be for as close to equidistant from the listener (for all channels) as you can manage. But even without delay circuits the modest change you see above will not have a major damaging effect. Since it is also quite popular, we present here it foryour consideration, along with the caveats. Next let's look at a more equivocal modification…

Symmetrical Surround Plan -- 5.2 Channels

On the other hand, there is also good reason for making the opposite modification of the front channels, like the symmetric plan. The 180 degree surround arc of sound has been nearly divided intofour equal angles, five discrete channels of sound, plus stereosubwoofers. My personal experience suggests that instead of going with themathematically exact division, yielding all angles of 45 degrees, thisversion is slightly better perceptually, with 40 and 50 degree anglepairs. It's probably splitting hairs, but try both and see if you don'tagree. We have a slightly more acute perception of angular displacement ofsound positions when both ears are nearly balanced, facing a central soundsource in front.

The above plan positions the LF and RF channels somewhatcloser together, nearer to C, favoring that mostsensitive area. This setup obviously requires a good, active centerchannel. Here I've shown the same smaller C speaker as before. Thesubwoofers take care of all the bass frequencies you could stand, sothat's not much of a compromise. Notice that for monitoring just fourchannels of "quadraphonic" material, the missing C channel would leave animpossible "hole in the middle" between LF and RF, if theabove configuration were chosen (40 + 40 = 80 degrees apart -- yikes!). Ifyou have to check on a lot of 4 channel material you'd be better off withthe first or second layout above. But for 5.2 channels of music, thisone's unbeatable

The Worst Surround Setup – 5 Channels

This is the worst possible use of five channels. Nowone of the black holes in the middle is filled in, leaving just three ofthem. The sounds up front are fine, wide and very decently positioned.There are no sound to the sides of those speakers, though. Everythingcomes mainly from within this right angle of two 45 degree sectors. Whatabout the rear channels? Well, they will be heard, of course, but thestereo will be poor compared with that in front. Not only is there nocentral rear speaker, but the back positions are, like before when youtried this yourself, not definitely locatable. Any poor stereo effect isnarrowed when it's completely behind us. Those two channels are beingwasted, just as they were with most quad sound in the 70's. Little wonderan honest public might be less than impressed, when confronted with thetruth of their own two ears.

5.1 Surround Sound for Films

Right, for music we want awider front image, as the 30 degree separation between LF and C and RFproduces. For film work that's usually not the ideal way to go. It's justa small modification, though, to move in the LF and RF channels as shownhere. This is a 25 degree version. Some theaters with smaller screensmight require only 20 degrees or less. Whatever value represents the mostlikely way your particular audience will hear your results ought determinethe way you'll want to setup your monitoring space. Right here we have anexcellent compromise for both music and film mixing and monitoring, butone that favors the film soundtrack to purely musical use. It will also bepractical in larger home installations, where the rear wall behind theviewing chair or sofa prevents any rear speakers anyway.

 The oneweakness here is the two angles of 70 degrees, LS to LF, and RS to RF.Those are about the maximum separation between any two speakers if youexpect imagery from in between each pair to "fuse", and not create "holes"in the soundfield (90 degrees is certainly too wide). That's one of ther easons to prefer about 60 degrees between each channel, except thefronts, where it probably ought be somewhat smaller (remember, our most acute directional hearing is up front). It's surprising you never hearsuggestions to divide the whole semicircle by five channels equally, placing the LF and RF even further apart, or about 40 to 50 degreesbetween each channel (no "holes" at all) as was described earlier.It would certainly work for music, whereas you'd need a 90 degree widescreen (curved?) to cover that LF-C-RF distribution! For home theaters thesingle subwoof version shown next may be an ideal startingplace.

 It need not be pointed out that we're not following any engraved set of "rules" here. You won't break any laws of any country or religion if you prefer to mix your music tracks using a narrowed frontsoundfield, or monitor your film mix with a front field so wide no screenthis side of Cinerama and Omnimax will be capable of covering it. Some engineers have reported that they find they can hear with more accuracywhen the speakers are wider than the screen, more like the suggestion above. Panned dialog and effects might not match exactly, but as thesenuances have been forgotten about (dammit) for over two decades, you canignore it, too. When mixing for films it's not often you'll encounter twosubwoofer channels. The so-called "Baby-Boom" of six track (70 mm) roadshow prints of only a very few major films since the late 70's haveused a pair of subwoofers. These were the former midway screen channels, LC and RC that mixers had stopped using when Dolby Stereo became the majorsoundtrack method. Since 70 mm had the extra tracks these often werechosen for low frequencies, only. Or the extra two channels would be usedfor Surround Left and Surround Right, and were then called "Split Surrounds". Most theaters, though went with the next plan.