Wired For Sound
Sydney Morning Herald
Monday May 6, 2002
The amplifier is the heart of an entertainment system. Its core function is to receive signals from your source components and amplify them to a level sufficient to drive your speakers - but modern amplifiers do much more. They can manipulate the sound as it passes through, altering its volume and tone, select between source components and often drive multiple pairs of speakers. Some will let you play CDs in one room and a radio program in another.
Home-theatre amplifiers often also allow you to choose sound parameters. They'll imitate a cinema showing action flicks or one showing art-house movies. You can dial up the acoustics of different venues to suit what's playing: a stadium for a live sports broadcast; a supper club for an intimate jazz concert or a cathedral to get some Bach organ music happening. Yamaha has a continuing project measuring the acoustics of famous performance venues around the world and many of these soundfields are found in its amplifiers and receivers.
More practically, home-theatre amplifiers let you choose between Dolby Digital 5.1 surround sound and DTS (digital theatre systems) surround. Early units offered Dolby Pro Logic sound, a far more limited format. Most new units offer Pro Logic II, which will add a surround sound effect to old video tapes and even ordinary stereo recordings, such as CDs.
A 5.1-channel amplifier provides five channels of surround sound - left, right and centre at the front and left and right rear, as well as a channel for the subwoofer, which is the "point one". Some top-order amplifiers now offer six and seven channels of sound in addition to a subwoofer track, the extra channels handling new formats that add a centre rear channel and/or extra channels at either the front (Yamaha) or each side (Onkyo).
You'll also hear the word "receiver" used. A receiver is an amp with a built-in AM/FM tuner, and comes from the old term "radio receiver".
The most important thing to get right is the power output. Your amplifier must have enough power to drive your speakers and to fill the room, while leaving a little in reserve. You won't need as much power in a small room as in a large one, even with exactly the same speakers, but it's almost impossible to have too much power - provided the speakers can handle it.
Extra power gives increased depth and immediacy to the music, mostly because instantaneous peaks of sound, such as the split-second a drumstick hits the rim of a snare drum, are handled better.
The only reliable measurement of power is the RMS watt, ideally measured into speakers of eight-ohms impedance, and this power must be delivered over the complete range of audio frequencies, from 20Hz to 20kHz. When power output figures are suffixed with "dynamic", "peak", or "PMPO" (Peak Music Power Output), the figure quoted is the theoretical maximum power that can be achieved for a split second under ideal conditions. It's always a far higher figure than the RMS output, which is continuous power that can be delivered for hours.
Most hi-fi speakers have an impedance of eight ohms, which is why the figure into eight ohms is the one to look for. When a speaker's impedance drops, an amplifier is able to deliver more power into it, so some manufacturers artificially inflate their power figures by quoting watts RMS into six- or even four-ohm speakers.
For most living rooms, a power output of 35 to 50 watts RMS a channel is sufficient, but if your home is very open plan or you want to drive very demanding speakers, you'll need more.
At the top of the market, amplifiers come as two separate components: a power amp that drives the speakers, and a pre-amp that selects the signal source to be amplified and allows you to make adjustments to volume and tone.
Amplifiers can influence the sounds they process, sometimes adding brightness, warmth or mellowness. The type of speaker that is connected always affects performance. Very few amplifiers will happily drive electrostatic speakers, for example, and many will misbehave if the speaker's impedance drops too low.
If you listen to vinyl records, ensure the amplifier or receiver has a "phono" input.
Many don't, meaning you'll have to buy a separate RIAA phono pre-amplifier to put between your turntable and the amplifier.
Redhot
Home cinema systems attract remote controls galore. Fortunately all of them can be replaced by a single, universal remote that, once programmed for your needs, will handle all major functions of your system. If you have a computer with Internet and some savvy, Marantz's RC5200 remote control is top shelf. The bad news is the price runs to four figures. Simpler programmable remotes start from a few hundred dollars. For more details call 1800 242 426 or visit www.qualifi.com.au
© 2002 Sydney Morning Herald