When the signal leaves the mixing desk, it is still at a very low voltage - far too low to drive loudspeakers. Its the job of the amplifier to deliver the power required, and manage the resistance or impedance between itself and the speakers connected to it.
Professional sound specialists often use amplifiers with switch-mode power supplies sometimes known as digital amps. This makes the amplifiers themselves much lighter - essential if you are using several in a rack.
However, for a small auditorium, or an up-and-coming gigging band, a good, powerful amplifier with a Class A design is usually enough. But just how powerful should it be?
Amplifier output is best measured in Watts RMS - for more details of what this actually means, see our Power Amplifier Online Advisor. The same measure is also applied to loudspeakers - they are rated according to the number of Watts RMS they can accommodate without sustaining damage. As a rule of thumb, the power output of the amplifier should exceed the capacity of the speakers by about 30%, and you should budget for about 50% more power overall than you will actually need. This will allow you to get a big, rich, warm sound, without distortion, even at high volumes. Here's a rough guide to room sizes and likely power requirements:
|Spoken word |
|50100 people |
room approximately 80-100sqm
(eg, entrance hall, gallery, small lecture theatre)
|2x 100 Watt|
|100250 people |
room approximately 200-400sqm
(eg, pub, club, small hall)
|2x 300 500 Watt|
|250500 people |
room approximately 800-1,000sqm
(eg, larger hall, marquee)
|2x 1000 - 2000 Watt|
Remember, these figures are only a rough guide. Ultimately, its down to your own judgement and taste to determine how much power you will need - but remember, it's not just about sheer volume. Clarity is more important that anything if you are going to impress your audience with your sound.