With Mike Oldfield’s seminal Tubular Bells now available as a stunning 24-bit FLAC 5.1 surround sound mix, we asked Andy Kerr how one should go about setting up a speaker system properly to get the best results.
Let’s start with the basics of a surround speaker set-up first.
Multichannel soundtracks are digitally encoded into multiple ‘channels’ of audio, each dedicated to specific tasks within the surround ‘soundfield’. In most instances, you’ll find audio channels dedicated to front, centre (dialogue) and surround signals, designed for replay through five speakers: two front, one centre and two rear.
These five channels are bolstered by a sixth dedicated solely to bass signals, called the Low Frequency Effect channel, or LFE. This channel contains approximately 10% of the audio information found on other channels within the surround soundfield – giving rise to the expression ‘5.1 surround sound’. In some soundtracks, additional surround channels of audio content have been encoded into the mix to add spaciousness to the sound: these are described as 6.1 or 7.1 soundtracks.
The perfect-world scenario
So that’s the content: how do you make the most of it? Let’s discuss the ideal world scenario first. The best surround sound experience comes from carefully matched, properly configured speaker systems able to accurately relay the full dynamic range of even the most demanding recordings. In an ideal world, you should use identical speakers in every location in your surround sound set-up, because that’s the only way to ensure consistency of both frequency response and tonality throughout your system. Said speakers should be positioned at specific points within your room, and at the same relative distance to your listening position, as stipulated in the standards set down by the ITU (International Telecommunications Union). This is a precisely defined layout for consistent multichannel recording and playback, often employed by studio engineers when mixing surround audio for both movie and music use.
Practical solutions to the problem
So that’s the purist approach: the real-world practice tends to be rather different, influenced in large part by the limitations of most listeners’ living rooms. For example, let’s say you want to use floorstanding speakers for your front left and right (stereo) listening, as many buyers do: what then? It’s not easy cramming five, six or seven full-sized floorstanders into the average front room. Even if you were prepared to put up with the aesthetic compromises involved, you’d need a very large room to hear the system at its best: large speakers don’t react well to nearby boundaries (walls!), so if you can’t give them the room they need to ‘breathe’, you could find they sound disappointing. Of course, a floorstanding centre speaker imposes its own, additional problem if you want to find space for a TV too…
So what are the practical solutions? First, wherever possible, buy speakers from the same manufacturer for every channel in your system. Even if they’re of differing sizes, using tonally consistent speakers is a fundamental part of proper speaker-to-speaker integration. Your surround receiver’s calibration system will be able to take care of the rest, compensating for any variations in speaker size and relative distance to your listening position – plus, if necessary, applying acoustic re-equalisation to the speakers themselves to compensate for any subtle variations in their performance.
All the same, doing your best to position your speakers correctly in your room is a worthwhile exercise. First, focus your system’s soundfield by positioning your centre speaker correctly. If you imagine a shallow, curved arc that runs through the plane of your main left and right speakers, the centre speaker needs to be placed at its apex, so that it sits right at the heart of the stereo image generated by your main speakers, and slightly behind them. It should also be placed equidistant between the two speakers, or as close as is practicably possible.
Next, try to align your centre speaker’s tweeter with that of the front left and right speakers. The easiest way to do that is to mount the speaker on a tall stand or fix it to the wall at the correct height. However, if you have to use a floor-mounted stand instead, borrow or buy a laser pointer and use it to help you align the speaker’s angle of tilt, either by raising up its front lip or adjusting the tilt on the speaker’s stand. Place the pointer near your speaker’s tweeter (carefully!) and then adjust the speaker’s tilt until the beam of light focuses on to the same position on your seat as similar beams aimed from your other speakers. This simple tweak can be extremely effective: in many cases, centre speakers are positioned to send sound to the listener’s kneecaps, not their ears, which doesn’t help clarity at all.
Finally, avoid bipole or dipole-type rear speakers (which spread sounds in multiple directions) for multichannel music listening. Their distinctive spread of sound offers key advantages for listening to film soundtracks, in that they better replicate the multiple-speaker acoustics of a cinema, but rear-speaker effects tend to be more precisely focused in multichannel music mixes. The specific dispersion characteristic of a conventional stereo speaker is a better solution. However, do ensure that your rear speakers are situated as far away from your listening position as your room allows: even if your receiver can electronically compensate for your rear speakers’ position, some physical distance between their drive units and your ears will help your sound no end.
How about my subwoofer?
The subwoofer is a vital element in a multichannel system. Every audio channel in a 5.1 multichannel mix is a ‘full-bandwidth’ signal (save for the bass, or .1, channel, as mentioned earlier). This means it offers the potential for deep bass from each speaker, offering extension down as low as 20Hz – far lower than the bass reproduction performance of almost every available speaker, save for the very largest designs. To ensure you don’t miss out on every available drop of sound quality from your multichannel music mix, and also to guarantee proper protection for your speakers when placed under severe sonic load, your surround receiver can apply a series of electronic protection filters, called ‘bass management’, which remove low bass from as many speaker channels as is necessary, before directing it onwards to your subwoofer. In most cases, this is an automated process, taken care of when you first calibrate your receiver.
All the same, you can help your subwoofer to sound better by positioning it correctly. A common school of thought holds that subwoofers can be positioned anywhere in your room, as bass is ‘non-directional’, but a spot of fine-tuning can notably improve your system’s speed and integration.
You can do that by putting your subwoofer next to where you would normally sit. Disconnect your speakers (at the receiver end), but leave the subwoofer connected, and plugged in. Play a loud piece of music, with a consistent bass beat. Walk around the room, listening to the bass as you walk. You’ll find it sounds louder in perhaps two or three places in the room (often, these are corners). Put the subwoofer in one of these positions, which are referred to as ‘nodes’. If this turns out to be behind you rather than in front of you, you may need to reverse the sub’s phase, using a simple switch fitted to its amplifier control panel.
Aside from the obvious dynamic benefits it can impart, a good subwoofer can also open up midrange details, contribute to musical bass lines and even match low frequencies into your room’s acoustic properties more effectively. However, a bad subwoofer will do more harm than good, by slowing your balance down, softening out your system’s attack, and generally make a ham-fisted sonic nuisance of itself. You’re better off having no subwoofer at all than opting for a compromised performer.
That’s it. Follow all these set-up tips and you’ll have a multichannel speaker system able to make the very most of the latest 5.1 music mixes, such as Tubular Bells – and in 24-bit FLAC quality, the end result will be a surround sound experience better than any you’ve heard before.