A common misconception is that the rated power of loudspeakers is a measurement of how loud they are and an amplifier has to have the same power output as the rated power of the loudspeakers it is used with. This is a very brief summary which dispels this misconception

 

To put this into some kind of useful information. I have driven loudspeakers rated at 300 watts with valve amplifiers that have an output of 20 watts per channel. The amplifiers drove the loudspeakers with consummate ease. The loudspeakers were what is called 'efficient' and the amplifier did not struggle. Similarly I have driven loudspeakers of which the rated power closely matched that of the amplifiers input and the amplifier struggled, these loudspeakers were what is classed as inefficient.

 

'Efficiency' is determined by sound output for a given input and is usually measured in decibels at one metre for an input of one watt. A good efficiency is usually about 90 dB, highly efficient loudspeakers may go as high as 102 dB and the lower scale efficiency might be 82 dB.

So, the lower the efficiency of the speaker the higher the power of the amplifier would need to be to drive it well.

 

One very important point to note is that a low power amplifier driving low efficiency speakers is not a good idea. It is often distortion caused by having the amplifier turned up too high which damages loudspeakers and this happens far more often than damage cause by too powerful an amplifier. If you find you are using the amplifier in excess of two thirds volume, or you often hear distortion, then the amplifier is probably not powerful enough for your speakers. (or you are deaf!)

 

The best thing to do is to try to match the amplifier with the speakers such that most of your listening is carried out with the amplifier at half volume. This ensures it is delivering enough power to hear the full frequency range clearly with a bit of power left for transient or fast notes and enough oomph left for good bass response.

 

This is all a bit of a science on it's own and my best advice is, if you really need to know more, to search Google for websites dedicated to loudspeakers, loudspeaker design and loudspeaker efficiency.

 

If the seller of the loudspeakers, or amplifier, appears to be a regular HiFi seller you should be able to get some useful information from them but don't except them to know all about your amplifier or speakers so if you want some good information you will have to give the specifications of the items you intend to partner.

 

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