In the case of most surround sound TVs, the left and right speakers are built into the TV cabinet.  Otherwise the following principles should apply.  The speakers should be placed at equal distances from the TV screen, each unit ideally no more than 1.5m from the set.  Remember that in the cinema the left and right channels are behind the screen, so if your left & right speakers are placed too far away from the TV, the sounds you hear will not relate to the on-screen action.  If you need to position your speakers closer to the set, you must make sure they are magnetically shielded so as not to distort the TV picture. 

The centre channel is probably the most important in the system.  Although the ideal is to use a speaker identical to the left and right pair, for cosmetic reasons most manufacturers produce horizontally mounted speakers for centre channel use with similar tonal characteristics.  This should always be mounted directly above or below the TV set so that any sounds related to mid-screen action (most of the dialogue, etc.) will seem to come from that point no matter where you sit in the room.  Centre speakers are always magnetically shielded with this purpose in mind.  If you have to mount the centre speaker on top of the TV cabinet, secure it there with a few blobs of Blu-Tack.  This sounds primitive, but the substance is very good for isolating vibrations from the TV cabinet.  It also makes it much more difficult to accidentally knock the speaker off the top of the set, which is worth considering if you have inquisitive young children.  If you have space, a separate shelf (or wall bracket) provides a much better support.

On just about every Dolby Pro-Logic/Dolby Digital amp there will be a CENTRE MODE control, typically with three options: WIDE, NORMAL and PHANTOM.  Why is this necessary?  Well, contrary to a common misconception, the centre channel in Dolby Pro-Logic and Dolby Digital does not just convey dialogue information.  It carries a great proportion of sound effects and music score also.  The CENTRE MODE control allows you to optimise the output of the centre channel to suit your speaker setup:

WIDE (a.k.a. WIDEBAND) mode sends the full frequency range of signals to the centre speaker, including some deep bass.  Ideally this should be selected where the centre speaker is of substantial size and - better still - identical to the main left and right speakers.  If you select WIDE mode for a smaller speaker the dialogue will generally sound congested and the effects will be bass-light.

NORMAL mode, as its name implies, is the option that the majority of system owners will use.  It applies to smaller centre speaker designs with similar tonal characteristics to the main pair.  Once selected, the centre speaker handles dialogue, music and sound effects convincingly, unburdened by the demands of the lower mid-range and bass which are diverted to the main speakers and / or subwoofer. 

Select the PHANTOM mode (a.k.a. NONE) if your room environment (or budget) cannot accommodate a centre speaker.  This mode simply mixes the centre channel information into the left and right front speakers.  If you can manage to sit directly between the stereo pair, a convincing centre "image" will appear. The downside of this option is that anyone sitting off-axis will find that the on-screen dialogue seems to come from whichever speaker they are sitting closest to.

In a real cinema system, an array of speakers at the sides and rear of the auditorium convey the surround information, which is monaural in Pro-Logic and stereo in Dolby Digital and DTS.  They are positioned quite high up to diffuse the sound so that the audience is generally not conscious of where the surround information originates.  Of course, it is generally neither desirable nor practical to have a dozen or so speakers in your front room.  To achieve the proper effect in the home with just one pair of surround speakers requires some forethought.

In a "long" room set-up, with the seating located in the middle of the room, it is best to mount the surround speakers on side walls parallel to the main seating position.  If they were mounted on the rear wall in this room configuration there may be a pronounced "hole" in the sound stage, with sounds "jumping" from front to rear rather than there being a smooth transition.

In a "short" room setup with seating on the rear wall you might get away with speakers being mounted on the rear wall.

In any case, surround speakers work best mounted at least 6 feet above floor level, wherever possible, to give the impression that the surround information comes from around the room in general rather than from specific points.  If you cannot mount the speakers on the wall, invest in some tall (1 metre plus) stands, available from such brands as Target, Atacama and Alphason.

Once all your speakers are in position, you need to make some essential adjustments.

Every surround sound component or system will have a "pink noise" test tone generator.  This signal moves from speaker to speaker to help you equalize the output of each channel.  From your favourite seat, adjust the volume on each channel until they sound about the same.  For more accurate channel-matching (or if you feel you can't fully trust your ears), buy or borrow a sound pressure level (SPL) meter to measure the output electronically.  Another adjustment is for digital delay, the amount of which will vary depending on how far apart your surround speakers are from the front channels.  The instruction manual will tell you what setting this should be for your system layout.  Those things done, you are now able to enjoy the Surround Sound experience.

You will find that while you are watching Dolby Pro-Logic or Dolby Digital material, the sound from the effects speakers may not be as loud as that from the front speakers.  This is perfectly normal.  Try to resist the temptation to increase the rear speaker level during performance as doing so tends to distract you from, rather than enhance, your viewing.

Once you have found a suitable location for your subwoofer (preferably away from a corner - see below for reasons why) and connected it to the dedicated SUBWOOFER OUT socket on your amp, you need to adjust its HIGH FREQUENCY CUT-OFF and VOLUME controls while the amplifier is running with some surround sound material.  Basically, the subwoofer should be adjusted so as to integrate seamlessly into the presentation of the rest of your system. 

The HF CUT-OFF determines the range in which the subwoofer works.  More often than not this is a rotary knob, allowing you to fine-adjust its output so that the sub takes over bass duties just where your main speakers start to let go. 

The VOLUME control determines the proportional output of the sub in relation to the main speakers.  In other words, when you raise the volume on your amp the bass level on the sub will rise proportionally.  You may have to take a little time to experiment with the settings, but the rewards will be worth the effort. 

If you follow all of the above advice, a lot of work can be undone if the room's acoustics are not taken into consideration.  If the room is square or has one dimension exactly divisible by another, resonances can be a problem.  Too many bare surfaces in a room (unadorned walls, large windows, wooden floors, etc.) can often make the sound harsh or tiring.

Fortunately, there are some ways of getting around these problems without resorting to pasting cardboard egg trays everywhere.  Substantial sofas, curtains and carpets are excellent for breaking up reflections and resonance effects, as are well-stocked bookcases and wall-hung rugs.  It is also best to keep speakers (especially subwoofers) away from corners as such locations have a tendency to exaggerate low frequencies, producing a boomy, muddy sound. 

It is often worth taking time to experiment with positioning of speakers to determine the best effect.  This will no doubt seem like a pain in the neck but you will thank yourself for your patience when you know you are getting the best out of your system.