Sound advice for home theatre audio

, posted: 12-Mar-2004 22:42

Audio is as important for a great home theatre experience as vision, yet it tends to be overlooked in the hunt for big-screen dazzle. As with screens, there is a bewildering array of audio gear to choose from, with prices ranging from $1000 all-in-one packages to electronic marvels worth tens of thousands. What do you need to consider for a sound home theatre solution?

AV receiver features
The heart of mid-range home theatre audio is the audio visual (AV) receiver. This amplifies the sound from TVs, DVDs and CDs, and works as the control centre of your home theatre set-up.

A receiver contains a radio, and sometimes a TV tuner. You can also get pure amplifiers that do not, as well as costly high-end gear where the components come in their own enclosures. You can pick up good units for $1500 to $3000.

The AV receiver needs to be well connected. Ideally, it should have component video inputs as well as optical ones for sound from the DVD player. You may also want inputs for a CD player, VCR and other equipment. Front-accessible inputs are a bonus for digital camera owners.

For surround-sound, 5.1 output (five normal speakers plus subwoofer for low frequency sounds) is the norm.
As well, 6.1, 7.1 and 8.1 receivers available for greater surround sound realism, as they give a true 360-degree sound stage.

To produce the surround sound, Dolby Digital and DTS handle the majority of 5.1 encoded DVDs, and Dolby Pro-Logic covers VHS tapes with surround sound, and some TV transmissions. These are a must.

High-quality digital-analogue converters (DACs) are also important; look for 24- or 32-bit DACs with 96kH or better sampling frequency.

Clean, honest power
Reproducing sounds faithfully is the name of the game. The power needed depends on the size of your room and the sensitivity or efficiency of the speakers. As a rule of thumb, for small rooms 30W to 50W is good. For bigger areas, aim for 100W or more.

Unfortunately, manufacturers use differing methods for measuring amplifier output. Many are questionable, like single total figures for the output - 500W or 750W for example.

"Peak output" figures (sometimes abbreviated PMPO - peak music power output) can also look impressively high. But neither method tells the truth. Instead, use RMS (root-mean-square) or, better, DIN (Deutsche Industrie Norme, the German industry standard).

When the amplifier isn't working, you want it to be completely quiet: no humm, no hiss or any other distracting noises.

Speakers corner
Unless you have lots of space and a big budget, home theatre speakers are going to be something of a compromise compared to those for normal stereo hi-fi. It's hard to accommodate five, six or even seven large speakers for surround sound so most home theatre set-ups use smaller so-called satellite ones.

The satellite speakers take care of mid frequencies and high frequencies, which are directional. Therefore, correct placement is crucial for the satellites: they need to be at the right height as well as place. Think carefully about how all this is going to fit in your room.

Low-frequency sounds are not directional (you can't tell where a sound under 200H comes from), so the subwoofer (low-frequency speaker) can be placed just about anywhere in the room. It's a good idea not to put it too close to the DVD/CD player or screen as the vibrations and magnetic field from the speaker element can cause interference.

Separate amplification for the subwoofer (built into the speaker cabinet, for instance) helps if the AV receiver
isn't the most powerful. Bass speakers shift a lot of air, and need a good amount of grunt to drive them.
With both satellite and subwoofers, solid construction is a good thing. You don't want the speaker casing to vibrate and colour the sound. Speaker costs vary greatly, but for a quality set from Europe or the US, expect to pay $2000 and more.

Listen carefully
Shop assistants often crank up the volume to levels that would have the noise abatement officers arrive if you did it at home. This can mask defects that you would otherwise pick up at normal sound levels.

If you are going to spend good money, take control of the volume and take some time listening to DVDs with good sound effects and well-recorded music somewhere quiet and reasonably similar to the room in which the gear will be set up.

Voice clarity is important for home theatre audio, so pay extra attention there. If you like music, expect to pay more for better receivers and speakers.

The package deal with everything in it may be a convenient buy, but does it sound as good as you want? If not, ask the shop if it can upgrade, for instance, the speakers to better units or do a similar deal with other components more to your liking.

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