Amplifier power - watts right for you?
Amplifiers are a funny lot. You can buy anything from an esoteric five-watt valve amp to a kilowatt of over-engineered power amp, all in the name of hi-fi. So how on earth are you to know what's right for you? How many watts you have and for that matter, how many you think you need are largely influenced by how loud you like to play, your environment, and the speakers that you are using. So before putting your puffed-out integrated on ebay for a current-hungry powerhouse, let's explode a few myths and take a guided tour through the high fidelity corridors of power.
The role of the amplifier
Amplifiers have three key duties - they must be adequate for the room in which they operate, control or drive the speakers they partner, and provide an acceptable loudness level for the way you play music.
Room size is key because the sound we hear is a result of both direct and reflected waves - a large room absorbs more power and requires greater pressure; therefore amp power must correlate with room volume. While you might find a 30 watt budget amp will drive a small box room, the Jones's hi-fi in their converted barn is likely to require a giant haystack's worth.
A crucial factor in determining how many watts you need is loudspeaker sensitivity, also described as efficiency. This figure, expressed in decibels (dB), describes the sound pressure level (or loudness) generated by the speaker from one given watt of power. Sensitivity figures give an indication of how easy the speaker is to drive a high sensitivity (95dB) for example, would produce significantly more loudness compared to a relatively low figure of 86dB, given the same power input. So if you're cursed with inefficient speakers you'll require lots of power to achieve higher listening levels(remember to check this figure when buying new boxes).
How loud you like your music will also determine your power requirements. If you're frequently upping the volume pot to 11 o'clock and more, then it's time to audition more power. What's more, to achieve a perceptible doubling in loudness, you'll actually need ten times more power. This is because power behaves logrhythmically - to play twice as loud as your 20watt amp, you're going to need 200 watts. The good news is that for Joe Average, with an average room, speaker sensitivity and appetite for loudness, 30 watts of good quality power is often plenty - this should provide a suitable level for domestic listening with varied source material.
So if you're content with the volume of your music, what can be gained from adding more power? The buzzwords are dynamics and control. Dynamics, the difference between the quietest and loudest peaks in a musical programme, require a certain degree of amplifier reserves. For most amps, a manufacturer will specify a 'continuous power' and 'peak power' figure. Continuous, as the name suggests, describes the available power for a prolonged period, and is the most reliable indicator of performance. Peak power however, describes the ability to provide maximum power output for fraction of a time (for example a kettle drum in an orchestra). So use peak ratings to gauge dynamic potential, and continuous to get a more reliable sense of power.
AVI Lab series integrated S21 MI
Control is frequently used to describe the way in which an amplifier uses its power reserves to manipulate the driver in a loudspeaker. With good levels of power on tap, an amp can 'grip' a large bass driver, making transient sounds (stop/start notes) appear rapid, punchy and agile. This desirable sonic situation gives music an increased sense of timing - fundamentally an essential ingredient of high fidelity sound.
So if you still feel the need to get more power into your system, think carefully about what it is you're trying to achieve. Big increases in volume will require big power, but dynamics, control and speed can all be bettered by adding those extra watts.
THREE OF THE BEST
Marantz PM7200 £330
The darling of the budget amplifier world, Marantz has done it again with another market leading, low-cost amplifier. For quality (especially in Class A mode), not quantity, look no further than this feature-bound workhorse from an excellent pedigree. www.marantz.co.uk
Rotel RA-1062 £595
A great-sounding powerhouse from a reputable stable, the RA-1062 pumps out a healthy 95 watts of rhythmic and transparent power. It's the pick of the bunch at its price point. www.rotel.co.uk
AVI Lab series integrated S21 MI £1,500
The amplifier everyone's talking about, the S21 is power, resolution and control all in the one box. This is the finest product to leave AVI's Gloscestershire factory for a good few years. www.avihifi.co.uk