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Digital surround sound is made possible by the recording of multiple, discrete, sound channels onto the soundtrack of, for example a DVD (“Digital Versatile Disk”) or HD (“High Definition”) television broadcast. Each channel is decoded, amplified, and reproduced on its own dedicated loudspeaker positioned to the front, rear, or side, of the listener, to produce an envelope or bubble of sound that “surrounds” the listening position. The sound emanates from a full 360° as it does in the “real” world, so the end result is an immersive, lifelike, listening experience. The choice of surround sound equipment, and its suitability to a particular listening space, the size, and placement, of loudspeakers, for example can make all the difference between achieving this effect successively or not.
Surround Sound Systems & Configurations
The common types of digital surround sound system are known as 5.1, 6.1 and 7.1 channel systems, referring to the total number of main loudspeakers plus a specialised “subwoofer”, which reproduces low frequency, bass effects (the “.1” in the notation) in the configuration. Dolby Digital, a 5.1 channel format, is the industry standard for DVD, and cable and satellite television broadcasting, with the result that the vast majority of surround sound systems used for home entertainment are correspondingly, 5.1 channel systems, featuring a front centre, front left, and front right speaker, together with left and right rear speakers, and a subwoofer. Extended formats, delivering 6.1 channels DTS-ES, for example or 7.1 channels, Dolby TrueHD or DTS-HD, for example do also exist, although they are not standard formats, and require one, or two, additional surround speakers to be experienced to full effect. Content recorded in 5.1 channel format can, nevertheless, also be played back on a 6.1, or 7.1, speaker configuration.
When it comes to putting together a digital surround system in your home, there are basically two choices; you can follow the HTIB, or “Home Theatre in a Box” route, by choosing a complete, integrated solution from a single manufacturer or the “separates” route, by choosing individual components; A/V receiver, loudspeakers, etc. from different manufacturers, yourself.
Even HTIB solutions vary in complexity, from manufacturer to manufacturer, but are typically straightforward and affordable with a simple A/V receiver, five matched surround speakers, and possibly a DVD player. Speakers do tend to be rather small, especially in entry-level systems, but if your budget is limited or space is at a premium, a HTIB solution can be practical and still produce surround sound of reasonable quality. A HTIB is an integrated system by design, so there are unlikely to be any connectivity issues, and because the supplied speakers are matched for tone, or “timbre” by the manufacturer, they may provide a more cohesive sound than speakers chosen individually.
Choosing individual components from different manufacturers may be more attractive, purely from the point of view of personal preference, and indeed, may ultimately provide sound of higher quality, if done carefully. A typical, entry-level A/V receiver, for example, is likely to perform all of the basic operations required; decoding Dolby Digital, and possibly other formats, amplification, etc. reasonably well, and offer a power output of between 50 and 100 watts per channel, which should be adequate for all but the largest listening space. Connectivity may be more of an issue, but connectivity options are usually adequate for most systems with the possible exception of HDMI (“High Definition Multimedia Interface”), which tends to be a feature of A/V receivers further up the price range – and the matching of speakers, for tone, and level, is a necessity.
The quality of an A/V receiver, and its correct configuration, is at least as important a factor as any other in determining the success of your surround sound experience. An A/V receiver needs to be configured from its own setup menu, such that it provides optimum performance for your particular number, and size of loudspeakers. Typically, speakers can be designated “large”(usually speakers with drivers of 6”, or more, in diameter) or “small”, and their distance from the listening position (or the corresponding time taken for sound to travel that distance, in milliseconds (ms)) can be specified. One of the fundamental principles of surround sound is that the tone, and level of the sound should not change as it moves from one loudspeaker to another. If it does, the source of the sound becomes identifiable, spoiling the effect. An A/V receiver can typically send a tone to each of the loudspeakers, in turn, so that its level can be measured by ear, or by using a sound level meter, and adjusted accordingly.
The centre speaker is probably the most important speaker in any surround sound configuration, as it is required to accurately reproduce voices, and dialogue. The front speakers, that is, the centre speaker, and the left and right front speakers, should be positioned equidistantly from the viewing, or listening, position, with the left and right speakers angled at 45° to that position, for watching films on DVD, or HDTV, and at a steeper angle, of 60°, for listening to music. It is important that the front speaker is not positioned closer to the viewing position than the left, or the right, front speaker. The three front speakers should also be positioned with their tweeters at the same height, roughly at ear height to a seated listener. It is often convenient to position a centre speaker directly on top of a television set, and if this is the case, it may be necessary to raise the front left and right speakers to a corresponding height, using adjustable floor stands, or fixed wall brackets.
Surround, or “satellite”, speakers typically, smaller speakers, which are positioned to the side, and to the rear, of the listening position should not be positioned directly behind the listener, as the sound emanating from them will be identifiable directionally, and will not integrate with the “soundstage” as a whole. Similarly, surround speakers should be positioned above ear height and directed across the listening space, rather than directly down towards the listener.
The other important component, of course, is a subwoofer, which reproduces the LFE (“Low Frequency Effects”) sub-channel in all digital surround sound formats, and is responsible for the vibration, rumbling and reverberation that brings realism to a film soundtrack. Subwoofers are usually, by their very nature, large pieces of equipment, and are not always easy to accommodate in the average living room, or other listening space. Ideally, a subwoofer should be positioned at the front of a listening space, a corner of a room is a popular location, in the same plane as the three front speakers. If this is not possible, for practical purposes, a subwoofer with “phase control” can be adjusted so that it reproduces pleasing bass effects wherever it is positioned in a room.
If your listening space is small, or unusual in shape, you may be considering wireless surround sound speakers. These certainly remove the need for speaker wires running from the front of a room to the back, but if you are envisaging a completely wire free solution, you should be aware that wireless communication via RF (“Radio Frequency”), or infrared, transmissions, is typically limited to rear surround speakers, and that mains power and therefore a wire to supply it, is still a necessity even for those speakers. Battery operated surround speakers are available, but generally lack the output power to deal adequately, with the demands of surround sound in the home entertainment context.
Above and beyond the technical capabilities of surround sound equipment and its positioning, the surround sound experience is also affected to quite a large degree, by the acoustic characteristics of the room, or space in which the equipment is situated. Rooms that are exactly square, or exactly twice as long as they are wide, for example, are notorious for creating resonance, and reverberation which can distort, or overpower the desired signal. Rectangular rooms create the least distortion of all but, once again the key is the correct, proportional, positioning of loudspeakers, so that the signals mix into a cohesive whole. In addition, bare floors, walls, and ceilings may cause reflection of sound waves, with adverse effects, although any such problems can be rectified fairly easily by adding a carpet, or curtains. The placement of a loudspeaker at the intersection of walls, that is, in a corner, or wall and ceiling, or wall and floor, is likely to increase its apparent bass output, and while this may be desirable for a subwoofer, it may not, in all cases. If your listening space is a particularly unusual shape, or constructed from unusual materials, which present severe acoustic problems, it may be worth your while to contact a professional home entertainment specialist, who will be able to advise the best possible solution(s) in your own case.