A Short Discourse on (Home Theater) Surround Sound

Here are home theater setup suggestions and a mini-history from the original THX to "now", and towards the future. If you're thinking about going from stereo to surround, or from 5 channel surround to 6 or 7 channel surround, read on...

Since everyone in HOME situations don't always build or install rooms using an acoustics consultant (or even a protractor) the results will vary and nothing is cast in stone. There are always personal preferences, decor objectives, etc. which override everything else. And while this is all my opinion gleaned from 55+ years in audio, your mileage may vary.

Everyone is entitled to operate their sound system as they see fit. If you enjoy it and it's right for you; great. But I like to assist people by getting all the wrong things out of the way first (speakers in the ceiling is always good for starters) so that you don't wind up with a room full of equipment which annoys you and you feel you're not getting the bang for the buck you feel you deserve.

I can't tell you whether to prefer red wine or white wine - that's up to you - but the careful convergence of setup ideas for the room acoustics, speakers, electronics, AC power, and wire hookup all play a part in the sum total of your overall enjoyment.

Whatever you do, enjoy experimenting. You could discover something great!

And don't forget that a sound (and video) system is definitely a weakest-link phenomena. ONE loose and crackling wire, in an otherwise pristine system, will cause the owner of the system to remark that the whole thing sounds like junk, or worse. I would suggest that the utmost care and attention be paid to what you might initially think is the smallest detail - such as contact cleaning and enhancing chemicals... and even labelling wires! You'll thank yourself later.

SOME PSYCHOACOUSTICS

Perhaps because of genetic, physical, or chemical attributes, some people are "Bass Freaks" or "Treble Freaks", etc. Some people will listen to a song and not even notice the bass is present, while some won't pay any attention to the singer but know every bass line. The point is people are different. You may like something completely different than what any artist, record producer, or engineer ever intended! There is, therefore a very wide range of what you might personally consider "loud enough" or "enough bass" or "too loud", etc. Fortunately the engineers at THX studied this very carefully and came up with a technical set of parameters designed to minimize the confusion.

The whole concept of surround sound is a complex psychoacoustic phenomena which if set up well is convincing, and if set up poorly is annoying at best, and becomes frightening to some, because people are not used to, nor prepared for, sounds coming from behind them without turning around to see what the sound is; and in the case of a movie this becomes a momentary distraction instead of an emotional concentration toward the screen.

Many people put surrounds too high or behind them -and then turn them up too loud and the result is not pleasant. Placing the surround speakers at the most desirable angles and getting the most desirable room coverage / splay will do wonders to smooth out the desired immersiveness of the experience.

My suggestion is to START with everything set at a calibrated, neutral position (and that includes the correct geometric placement of the speakers as I will explain) and then work outward from there, continually fine tuning your system mechanically and electrically until you feel it sounds right to you. This is not a trivial issue. Expect to spend a few weeks at this.

There are methods of setup which are DESIGNED and SUGGESTED if you want to experience the seat-of-your-pants, this-is-how-they-hear-it-in-Hollywood type of setup. There are suggested setups for those who might like classical music and like the feeling of being, for example, in the 5th or 15th row center. This also brings up a whole series of questions such as, "How was the piece mixed? From whose vantage point? From the guitar player's perspective? From the conductor's perspective? From the 5th row center concert seat? Nowadays, DVD's with movies on them intended for home release are specifically mixed with the intent of being played back in a home setup, where the speakers are essentially near to mid-field, at perhaps 4 to 15 feet from the listeners' ears. The soundtracks for the Theatrical release of the same film is usually different: it is intended for playback in a much larger space, with the speakers much further away to begin with, and therefore the spatial characteristics that are an integral part of the mix are different between these two different releases.

One way to approach this entire setup phenomena is to get the stereo image correct first, before concentrating on the overall home theater experience (meaning 'surround sound' ) as a whole. Some people concentrate only on the picture and the visual phenomena, and then stick some speakers up wherever they can. That result is often disappointing. If, after the system is completely set up, you find yourself "leaning in" to the sound, subconsciously trying to get "closer" or "more immersed" in it then I would suggest repositioning your seating so you are somewhat closer to the picture, then reorganize the speakers. Sometimes a good way to determine speaker placement is to set up ladders with boards between them and keep moving things around until you are convinced things are the way you like them. Another method might be to hire an acoustics consultant/studio designer to get it right the first time!

BRINGING THE MOVIE THEATER HOME

Besides the simple psychoacoustic effect of the stereo image, there is an even larger psychological effect when the sound is coupled to picture. The HIGHER and WIDER the placement of the L and R speakers are the more "Hollywood" the effect. The closer together and lower the L and R are (to a certain extent) the more "intimate" the effect.

The Center Channel is mostly for dialog, and the L and R are mostly for M&E (Music and Effects). Historically, music engineers/mixers have only had a stereo pair to work with, and all the LR placement and panning heard by you the listener was based on the psychoacoustic phenomena of the phantom center channel.

But movie engineers and mixers have had a REAL center channel to work with, and so operationally we now have the following sub categories:

Music mixed in stereo
Music mixed in surround (5 channels)
Film mixed in surround for the theatrical release.
Film mixed in surround for the home DVD release.

Different film mixers and rock n roll mixers have rather varying operational philosophies about all of this. Do not expect to play a movie DVD and then switch to a rock n roll CD and then switch to a classical CD and not expect to have to adjust things. This brings up a serious point: Just because you think your system is calibrated, there is such a wide range of program material differences that you essentially MUST adjust each and every disc -- perhaps each and every song, if you want to lean towards being an audio perfectionist.

For the movie, the real C channel is essentially for dialog, and therefore should be placed as close to the spot on the screen where the actors mouths are! Unfortunately this means right in front of the picture, which of course we typically cannot do... so in the case of a projection screen, it MAY be advantageous to place the speaker behind a perforated screen; in the case of a tube, Plasma, or LCD picture it should be placed below the picture if possible. The L and R can go somewhere near the centerline of the picture, or a little higher. The L, C and R tweeters do NOT necessarily have to be lined up as long as they are not too far (many feet) away from being in a line. In other words, if the C is below the picture, the LR might be on a line 2 or 3 feet above where the C is. When figuring out these angles and setups, it is a good idea to make the subtended angle of the L and R speakers 60 to 75 degrees, with 60 degrees being the preferred number. More about this will be shown in the diagrams below.

Placing all 3 front speakers too high up such as in a row above the picture near the ceiling is generally not a good idea and is to be avoided whenever possible. Among other acoustic anomalies, this often causes the audience to "lean in" to the sound, tightening the occipital muscles as opposed to relaxing them, and the result is an experience which leaves the viewers tense, not relaxed.

However there is an interesting phenomena with a moderate room and the subwoofer in the front somewhere: when the younger 'kids' are sitting on the floor as they often do, they love the bass. So they are sitting nearer the sub and the higher frequencies are splaying sort of over their heads. The more mature and elderly, who usually do not like bass so much, are more in the direct field of the higher frequency drivers, and also get somewhat less bass. So now, rather than attempt to get the sound "the same" everywhere in the room, (the concept of making the room "flat") we have used the natural acoustic phenomena and anomalies of the room to accomodate the auditory desires (real or imagined) of the listening audience. Do not underestimate this phenomena! I would suggest getting the sound "right" for your main "sweet spot" seating area, and allowing the natural sound patterns in the room to then be used to their full advantage --- even to the point of intentionally UN-balancing the room somewhat. Use the anomalies of the room to your advantage! Have a mother-in-law who hates bass? put her in the null. Now everyone is happy.

Once the speakers and the sound system is adjusted properly, it should essentially disappear into a continuum of surround sound, where the localization appears real and smooth; which is to say if some dialog appears as if its coming from over your head then it isn't set up correctly!

THE STUDIO vs THE HOME

In a studio, the front speakers are usually placed in an arc because we're really dealing with panned mono signals, and the easiest way to help to ensure that all the levels are the same, and in true electrical phase with each other, is to place the speakers the same distance from your head, in an arc. But at home, many people simply put the speakers on a straight line and adjust the levels [to be the same] accordingly.

The EARLY DAYS of HOME THEATER - ENTER THX

Once we get past the phenomena of stereo, we arrive at the next historical stop: the suggested THX setup with DIPOLES placed at 90 degrees. The listener is sitting in the null of the out-of-polarity (often somewhat incorrectly stated as 'phase' - they are actually "180 degrees out of phase") surround dipoles, and the dipoles are splaying the Ls Rs outward along the walls of the room. This decorrelated [side] splay gives the listener the sense they are in a large(r) theater.

Fig (1) - one of the original THX SETUPS

Notice in the above diagram there's NOTHING behind you. (Of course many people place the surrounds "anywhere" because that's the only place they'll 'fit' or 'go'.) Some people put the "surrounds" in the back, or incorrectly stated, in the "rear". This is psychoacoustically and psychologically wrong. Tom Holman (and others, including myself) found, after much experimentation, that sounds from directly behind frighten the young and the elderly, and in fact detract from the theatrical experience, and cause people to turn their attention away from the screen toward the offending sound.

The THX phenomena did and continues to do a lot for the industry by not only specifying minimums, and by continually exceeding these minimums and raising the bar so that manufacturers are always striving to build a better product. If you were to do nothing else than buy all THX approved products, and blindly hook them up, and set the switches to the THX position, you would at least be assured of a minimum theatrical experience which is quite respectable and satisfying, even if you were not an audio, nor video, nor home theater expert. Often, this is the best and certainly easiest choice.This makes the entire setup painless and almost plug-and-play!

Even following the THX guidelines, you can expand and extrapolate on their good foundation by making things "bigger"; specifying for instance a higher powered version of all the equipment so that the overall experience is maintained at a high level but there's MORE of it still.

Of course all the great equipment of the world cannot sound good if it is hooked up wrong, adjusted wrong, or set up in a space which is an acoustic nightmare. You would not want to listen to the best speaker in the world if it were placed in a glass shower stall with continuous reverberation which builds up to complete distortion. Therefore there has to be at least some attention paid to the room acoustics and its acoustic surroundings, which become part of the overall audio (and theatrical) experience.

There were some speakers intended for "surround use" which were dipoles, as originally suggested by the THX setup, and as shown in FIG. 1. There were also some speakers which were just like the speakers at the front of the room, i.e. "front-firing", (out of the front of the cabinet) and these were placed at the Ls Rs surround positions.

Then Ken Kreisel at M&K invented the Tripole, people in studios put the Ls Rs at 110 degrees of arc from the "C", the ITU and the AES published their suggestions, and that gives us the world "standard" 5 channel surround sound setup. This is typically how things are set up, monitored, and mixed in studios.

Fig (2) - Typical 5.1 suggested setup.
This is the STANDARD SUGGESTION for "SURROUND SOUND".

This diagram does not presuppose you put speakers in a circle - although that would be best. The supposition is you extend the angular lines outward until they intersect a wall and you put the speakers on that wall. IF front-firing speakers are used, (at the Ls Rs positions) you aim them as shown. If TRIPOLES are used, you place them flat on the wall, so that the correct ratios come out of the [sides of the] box and splay on the walls.

6.1, 7.1 and MORE

Many receivers have a combination of proprietary "surround " modes which support a 6th or a 7th additional speaker. To make a very long issue short these surround modes are usually digitally synthesized and additionally processed and reverberated from the original 5 channels. I suggest to most people that the better path is to set up a "better" 5.1 system (which is how things are mixed) than a more diluted 6 or 7.1 system. Merely adding sound sources to a room does NOT enhance intelligibility in any way --- to the contrary, often you are adding 2 more sources but have not changed the relative levels of the rest of the speakers therefore the relative level of the all-important Center dialog channel is now lower!

The setup below shows a typical setup using a moderate to high-end home theater receiver or control center such as a Denon, Marantz, Pioneer, Harman, some Yamahas, etc. They typically have a pair of Lb Rb outputs which for the most part ARE NOT DISCRETE! They are resynthesized from the 5 channels that already exist, and the signal(s) sent to the back contain either a simple delay and/or artificial reverb and digital processing to MAKE THEM SOUND AS IF THEY WOULD IF THERE WERE REAL CHANNELS BACK THERE. Certain decoding methods, such as DTS have one (6.1) or more (7.1) channels and those 'extra' back channels are synthesized and then encoded AT THE TIME OF ENCODING, therefore they are already on the disc.

Certain other companies, such as Yamaha and Lexicon, have their own proprietary surround resynthesis schemes which sometimes suggest that speakers be placed in locations that can only be described as "unconventional". Even so, some of the schemes, although considered odd by the engineers and producers who set up and mix the original music, are nonetheless very interesting, proving that the art of audiophile experimentation is not dead!

To take this even one step further, Tom Holman has demonstrated a 10.1 channel sound system, (and more...) and as the software upgrades for the various receivers and decoders matures, we may expect to see all sorts of unusual and proprietary processing tricks emerge.

In some rooms which have a ratio of very long to wide; or are acoustically 'dead' or dampened, the addition of these channels 6 and 7 MAY be somewhat beneficiary. The overall suggestion is to not go to a 7.1 setup if it is going to compromise the "correct" 5.1 setup in ANY way.

FIG (3) - 7.1 Channel setup for the home theater

If you feel you MUST set up 7 channels, do it this way. The angles of the Lb Rb speakers becomes part of a psychoacoustic balance: if you think there's sound that DOESN'T BELONG behind you, it will be frightening. If it properly blends into the scenario of the film and the rest of the acoustic phenomena happening in the room, it will feel "correct". It would seem that firing a speaker right into the back of your head cannot be correct. My suggestion is to make the back pair about half the subtended angle of the front pair, therefore about 30 degrees a part. See below for some other alternative surround setups (either 5.1 or 7.1).

But here's a catch: we don't actually need Lb Rb; (the back channel resynthesis) we can make this 2nd pair of surrounds ALSO be Ls Rs, just like in a movie theater, where there are almost always multiple sets of Ls Rs. In fact we can have multiple rows of listeners, and multiple rows of Ls Rs; all we need are (usually) dedicated channels of amplification to drive each "pair, like this below:

Fig (4) - Multiple Surrounds, such as in a larger home theater presentation room,
with multiple rows of seating.

You will notice that the surrounds are placed so that each row of listeners gets hit by a surround pair at about 110 degrees of arc from the C spaker. So Surround sets 1 and 2 can be Ls Rs, and surround set 3 can be EITHER Ls Rs -OR- Lb Rb, depending upon if the receiver in question supports it. There is absolutely nothing wrong with using multiple sets of surrounds. Some receivers have the option to adjust the delay timing to these multiple sets, so that the additional few milliseconds of delay to these "rows" makes the room seem larger.

In some instances, notably if the room is reflective, close to square, or the entire listening area is quite small, the addition of a Lb Rb pair may muddy up the whole thing and may detract from the intelligibility of the C channel dialog, because you're adding 2 more uncorrelated sources, with different delay timing into the equation, and this muddys up the entire soundfield. This may cause the C dialog channel to be less intelligible because now the Center dialog channel represents LESS of the overall averaged sound level.

In a room which is very rectangular, (and it depends where you are sitting in this room) very dead (plush carpets, wall hangings, soft furniture, acoustic trapping) the Lb Rb surrounds may be VERY beneficial.

A "REAL" CENTER CHANNEL vs A "PHANTOM" CENTER

What's the future? The industry, now that real multiple panning output plug-ins are available for DAW's, may be moving in the direction of "Panning Pairs" that is, where every pair of adjacent speakers has ITS OWN PHANTOM CENTER IMAGE, just like a stereo L R has its own phantom center.

The film industry has ALWAYS had a center channel speaker for dialog, and places M&E (Music & Effects) in the L and R.

The MUSIC industry, (i.e. rock n roll, classical) has NEVER had a discrete Center channel; they have always used a PHANTOM center image formed between the L R. This has formed a remarkable dichotomy in the world of mixing which is continually unresolved. "Where do we put the voice? In the C only, with a little reverb in the LR?" (that's the film mixer talking) vs "Where do we put the voice, in the LR with some in the Center to make it "feel " correct? and if we have the voice in all three, then what happens when it's downmixed to stereo? We're not used to this available Center channel --- help!!!" (that's the music mixing engineer speaking...) There are always issues and workarounds.

So now if we put every pair of speakers 60 degrees apart, that gives us this: (6 x 60 degrees = 360 degrees; while the 7th speaker [the Center] is ALWAYS separate and distinct). That setup then looks like this:

Fig (5) - 60 degree splay setup - part of what the future may hold...

Now there's a phantom center image between each pair, (between L and R; between L and Ls; between Ls and Lb and so on, around the room) and yet the speakers are "placed" in the room in such a fashion as to be approved by spouses (of any gender) and interior "designers" and "decorators". The setup becomes "easy".

This gives fabulous spatial localization even with systems which have less than ideal phase linearity (important) or frequency linearity (somewhat less important); or where, say, one set of speakers on one side of the room is higher than on the opposite side of the room, because that's the only place you could "stick" them.

But guess what? !!!!! The Ls Rs are at 90 degrees to the 'main' listener again, just like in the original THX setup, except that the original THX setup called for DIPOLES at the sides and these later diagrams call for front-firing speakers all around.

One very desirable solution is to set everything up so you can, in fact, hear everything how the producers, directors and engineers intended, and this holds true for both the visual, the audible, and the sum total of the theatrical emotional experience.

Once you understand that entire philosophy, then you are able to modify it, if you so choose, to fit in with your lifestyle, room decor, budget, and technical adjustibility, so that the end result is most pleasing to you.

MONITOR or PLAYBACK?

You could also strive to make your room seem like a pro studio, setting up the room with the speakers not necessarily against the walls, but in a much tighter circle as shown in the diagrams, perhaps, say, in an 8 or 9 foot diameter circle. What that does is tend to focus you in this tight sound [near]field, where you hear every nuance of what is in the mix, and LESS from the room; kind of the opposite of the philosophy of widely splaying tripoles (or dipoles). You are in the nearfield, and you do NOT really hear the first order reflections, because you are so tight in the circle. By the time the sound hits the walls and comes back to the inside of the circle, the Haas or precedence effect has long since taken over, and the room splay now becomes a much smaller percentage of the overall sound.

For an even added tightness, and the MOST up close and personal mix possible, treat the room acoustically to help make it flat, neutral, and have little or no first reflection and THEN sit inside the 'small' circle. The widely splaying effect is great for relatives, friends, neighbors, lookers-on, and so on, but there is nothing so personal as being in your own self-contained, focused, field of the mix; sort of flying in the cockpit as it were as opposed to "looking out the side windows" as an uninvolved passenger...

One last word about this 'small circle' setup: this becomes the most effective way in a smaller apartment where you would want to bother the neighbors the "least" --- since you are sitting 6 to 10 dB CLOSER to all the speakers than might otherwise be the case, you have all the added benefits of the initmacy and a wider dynamic range, because you're "starting" with the speakers turned down 6 dB. Therefore you just gained a "free" 6 dB additional headroom and dynamic range.

If you have the time, patience, and room, experiment with this circle starting as small as possible and then extending the so-called circle out to the room's boundaries. You just may find the magic combination FOR THAT ROOM where the direct, nearfield sound properly balances out the room's own refelectivity, and this then makes the entire system disappear, and the surround field, even with a 5 channel system, seem quite seamless.

For some interesting reading on room acoustics and how to preserve the acoustic balance and purity in a Home Theater room check out Art Noxon's articles at the ASC / Tube Trap site:
http://www.asc-home-theater.com/ht-articles.htm
Click on the Volume I, II, III etc links, not the PDF versions. The link to each of their next page is WAY, WAY down at the bottom of each page.

For a very interesting and somewhat differing view on subwoofer placement, read Floyd Toole's article here:
http://www.harman.com/wp/pdf/multsubs.pdf   PDF file, 815k