Articles and whitepapers

Loudspeakers for High-End Home Cinema (1/3/2004)

By Richard G Elen

Home cinema, or 'home theatre' as it is known more commonly in North America, developed largely as a result of the availability of high-resolution - particularly digital - sources of movies and music, notably the DVD (Digital Versatile Disc).

Thanks largely to Dolby Laboratories, and latterly Digital Theater Systems (DTS), home theatre has also heralded the introduction of surround sound into home listening environments for the first time since the demise of 'quad,' some thirty years ago.

In most cases, the same audio system will be used to replay both music and movie soundtracks - the former traditionally in stereo, although today, with the advent of media such as DVD-Audio (the audiophile-quality extension of the DVD format), surround music listening is becoming more common. Loudspeaker size - and budget - also has implications when it comes to how the system handles low frequencies, and all these considerations can make the choice of home theatre loudspeakers, and the systems that drive them, particularly confusing. This article will attempt to unravel some of the challenges and provide some suggestions to be borne in mind when considering suitable loudspeaker systems for home theatre applications.

Surround sound

The standard loudspeaker configuration for a surround home theatre system is so-called '5.1', the '5' describing to the five main channels, Left Front, Centre, and Right Front, and Left and Right Surrounds, the '.1' referring to what was originally a bandwidth-limited channel specially designed, in the cinema, for low frequency effects, referred to as the 'LFE'. Today you will also find more complex systems that include side speakers (7.1) and even height, but we will cover 5.1 in this article as a starting point.

The difference between the subwoofer and the LFE

A major source of confusion in the minds of most people when considering systems for home theatre, is that mysterious LFE. It started life as a special analogue cinema sound channel for sub-bass effects, such as asteroids falling to Earth and Tyrannosaurus Rex footfalls - these sounds were given their own channel because they might otherwise overload and distort the other analogue channels. Now that we have full-bandwidth digital channels in distribution media such as DVD, there is less need for such a channel (and no need for it at all in music, where there are no asteroids), but there it is.

the Meridian D2500 subwoofer

The easy mistake to make is to equate the LFE with the 'sub-woofer' (or sub) - one or more loudspeakers designed to handle bass in your home system. The LFE is not the 'sub-woofer channel' and you will get into trouble if you think it is. When the channels from the disc enter your surround processor, the processor's bass management system filters the low frequencies out of the feeds to speakers that cannot handle them and feeds them to loudspeakers that can - either large, full-range speakers, or the sub, or both. And the processor, not the player, is where bass management should be, incidentally.

Speaker performance

You can have one of several different loudspeaker configurations in a home theatre system. Ideally, all of your loudspeakers, except the sub, should be identical, and all should have full-range response, i.e. they will handle the entire human audio range. However, if you have difficulty in placing large speakers such as this in the room, the important thing to do is to ensure that at least the front speakers are full-range, if at all possible.

Meridian G Series full-range speakers in a home theatre setup

When building your speaker system, do not forget the importance of the Centre Front (CF) loudspeaker. You will find that it is often unused in surround music (and, of course, stereo) where many recording engineers feel, with some justification, that it is unnecessary; but in the case of movie soundtracks, this is where much of the dialogue will originate. There are also systems such as Trifield, which use the centre front speaker to build a more accurate, smooth and integrated stereo image, and in this case too, a speaker that sonically matches your left and right front speakers is ideal. Some manufacturers offer a special version of their main speakers for use as a CF speaker, that is designed to mount horizontally below or behind the screen.

If you can use full-range speakers all round, then you may not need a subwoofer if your primary diet is music. If you watch a lot of action movies, however, or if you have some speakers which are less effective in the bass, then a subwoofer is a valuable component in your system. Be sure to set up the bass management system correctly in your surround receiver or processor by telling it which speakers are 'large' (can handle bass) and which are 'small' (and cannot). Bass that cannot be handled by a given speaker will be fed to the sub, along with any sub-bass from the LFE channel on the source material.

If you are building a special listening room, and especially if pushed for space, you might consider in-wall loudspeakers for the surrounds. These can sound excellent, although they do need extra planning and effort in installation.

Active and passive speakers

There are two basic types of loudspeaker: active and passive. The conventional passive loudspeaker is fed by a separate power amplifier, via what can be difficult-to-hide cabling. There can be quite significant losses of quality as a result of the passive crossover in such speakers, used to separate high, medium and low frequencies.

Active loudspeakers, made by companies such as Genelec, take line-level signals from your processor and have the amplifier actually inside the loudspeaker cabinet. This means smaller, easier-to-manage cables going to the loudspeaker and, most important of all, because the amplifiers and loudspeaker drivers are directly connected to each other, the sound can be much more effectively controlled, and a relatively small cabinet can sound like a much bigger one. The downside is that you have to plug them into power sockets.

The Genelec HT210B two way active speaker designed for high quality home theatre systems

The DSP loudspeaker

The ultimate in this kind of approach is the DSP loudspeaker, such as those made by Meridian, in which digital signals are fed to the loudspeakers, and the crossover is implemented with digital signal processing (DSP), for superior signal handling, before feeding it to specialised digital-to-analogue converters and amplifiers, and thus to the drivers. A system of this type, in which the signal essentially remains in the digital domain from the studio to the speakers, can offer the ultimate in home theatre enjoyment - although this approach is not inexpensive.

Speaker configuration

When it comes to arranging your loudspeakers, bear in mind that for good stereo music listening you will need your left and right front speakers to have an angle of 60 degrees between them when you are sitting in your favourite listening position, i.e. the 'sweet spot.' The centre front speaker should be placed in the centre - below, behind or possibly above the screen. The official standard for movie sound suggests that front left and front right speakers should be further apart than 60 degrees (in a cinema, they might be either side of the screen), but if you try this, you will find that the stereo image will have a hole in the middle when you listen to regular CDs and other stereo material (unless you are using Trifield) - so resist the temptation.

The surround speakers should be behind you, the same distance away, with an angle of around 120 degrees or a little more between them (this is not ideal, but it is the standard that has emerged). They can also be placed on either side of you. The diagrams in your surround processor or receiver's manual or on-screen set-up system will help, and you should also arm yourself with a surround set-up disc, such as that offered by Chesky Records. Be sure to specify the speaker distances from the listening position in the processor's set-up, as well as defining their sizes and telling it whether or not you have a sub.

the Chesky CHDVD221 Ultimate DVD Surround Sampler & 5.1 Set-Up Disc

Well-chosen and, especially, correctly set up, a good surround speaker system will open the door to truly stunning movie and music experiences. You will be glad you did it properly!

Richard G Elen is the Creative Services Director of Meridian Audio Ltd.

www.meridian-audio.com