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Surround-sound

 

SIMPLE AND PURE

 

 

Keep It Simple Stupid – or KISS. This applies ot Surround Sound too, says Noel Keywood.

 

 

 

surround-diag-web

 

For music, four loudspeakers are enough.

 

 

To most people, having four loudspeakers behind the settee and three in front is conspicuous madness, and AV (Audio Visual) is the standard bearer. This 7.1 arrangement is for Home Cinema though; AV can also handle all forms of surround-sound audio well – and you don't need seven loudspeakers to enjoy it. In this Knowledge article I will look briefly at the loudspeaker issues, and why you don’t necessarily need a 5.1 system to enjoy music from Rock to Classical, on LP through to Blu-ray. In truth, you are better off using fewer loudspeakers, of higher quality than is common in Home Cinema, to get really magnificent surround sound.

And here’s a little thought. Highest quality digital audio (24/192, meaning 24bit resolution at 192kHz sample rate) is available on Blu-ray disc in surround-sound (see the 2L disc catalogue) and music concerts are often 24/96, better quality than CD. If you want to be able to enjoy this quality, you must have a true high fidelity surround-sound set up; an AV Home Cinema system isn’t good enough.

Home Cinema was conceived to support Hollywood movies sold on DVD and, now, Blu-ray. It uses cinema practice of a centre audio channel for dialogue, left and right loudspeakers for frontal sound effects including music, and rears for rear sounds, plus subwoofers to handle the rumbling sounds of earthquakes, explosions etc. That makes 5.1 channels in all (the 0.1 is the subwoofer).


loudspeakers-5.1-converted


A 5.1 surround-sound system in ideal layout.



Clearly, industry minds have thought, there aren't enough loudspeakers here; a large gap exists at the rear. Nature abhors a vacuum, and the Consumer Electronics business abhors unoccupied floor space even more, so 6.1 was born, shown below. Here a single rear loudspeaker sums the left and right surround channels to produce a solid sounding centre rear image. Fertile minds quickly saw opportunity and 6.1 soon became 7.1.




loudspeakers-position-6


A 6.1 system has one extra Rear loudspeaker.



A specs. war was behind the push to 7.1, the extra two channels feeding Back loudspeakers. The signal to them is synthesised from the Surround (rear) loudspeakers, because 7.1 recordings don't commonly exist, nor are they likely to. The Backs just fill in the rear sound field, but they still demand extra power amplifiers and cables of course. The same comments apply to 10.1 and the frontal height channels of Dolby ProLogic IIz.



loudspeakers-position-7


A 7.1 system uses two Rear loudspeakers for a more even rear sound field.



Seven loudspeakers and a subwoofer for explosions are unnecessary for music, as well as domestically unacceptable to most people. Manufacturers are aware of this so receivers can be reconfigured in their set-up menus to alternative arrangements. The most common is to reallocate the Back channels to second room use, or to bi-amp front Left and Right loudspeakers. This can only be done with bi-wirable  loudspeakers though, where it brings about a small improvement in quality by cleaning up and tidying the sound through a small reduction in muddle (see our Amplifier section).




bi-amp-2


In many receivers spare Rear channel amps can be re-configured to Bi-amp the front loudspeakers, improving quality.



In most homes, the only position for the Centre loudspeaker is below the TV – but this is a bad position for high quality music reproduction, channelling lead singers, drums and centrally placed instruments through a small loudspeaker close to the floor. It may be OK for cinema dialogue, but it’s unrealistic for music, constructing a sound stage that arcs downward to floor level at centre, unlike a normal stereo stage that arcs slightly upward between the loudspeakers, a perception created by the ceiling reflection.




front-diag-web


Centre loudspeakers are poorly positioned for vocals, and even movie dialogue. .

Worse, a Centre loudspeaker commonly produces centre channel dominance, or Mono - an unfortunate contradiction of what surround-sound is meant to be!  And finally, although it carries much of the music, a Centre loudspeaker is limited in size and quality compared to Left and Right fronts.

The simple, convenient solution to this is not to use a Centre loudspeaker, switching off the Centre channel in the receiver set up menu. This directs the Centre signal to Left and Right channels equally, resulting in normal stereo with its phantom centre image, an action that reduces centre channel dominance and restores quality by utilising the high quality, matched Left and Right speakers.

Eliminating Back and Centre loudspeakers, and making the rear Surrounds small full range hi-fi types results in a surround-sound system that is little more intrusive or costly than a stereo system. Cabling can be the biggest headache, as a door may be in the way to one of the rear 'speakers, forcing a longer run around the other side of the room. All the same, a ‘quadraphonic’ system like this handles movie sound tracks well and is as unintrusive as is possible.

In a system using full range hi-fi loudspeakers, for music a subwoofer becomes unnecessary. Specifying the Front and Surround loudspeakers as Full Range in the receiver's set-up menu, and subwoofer as Off eliminates bass management, putting all frequencies, including lows, through the four loudspeakers. You will lose deep subsonics from film soundtracks, so dinosaurs will develop a lighter step, but does this matter? There is usually little of consequence in the LFE channel of music discs; what to put there is an artistic decision made by the surround-sound mixing engineer and LFE is often ignored.


LOUDSPEAKERS TO CHOOSE

The usual advice is to use Surround rear loudspeakers that have similar properties to the Fronts so they are equally voiced – and that is fine. Most manufacturers produce a range that covers this requirement, with floor standers suitable for Front use and smaller stand and shelf mounters for use as rear Surrounds.


Live concerts on DVD and Blu-ray usually put audience noise and ambient information through the rears, so they have little to do. However, some discs, those from 2L for example, place the listener at the centre of the performance and here the Surrounds need to be of good quality. A large stand mount model is generally adequate though.

 

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