With speakers exerting the most influence on sound quality, how do you choose the right ones for your movie room? By Simon Campbell.

The job of a speaker is to reproduce the sound embedded in a DVD or CD ? or any other audio source ? so that it sounds exactly the way it did when originally recorded. In truth, though, none achieve this. Other equipment in the audio chain plays a part, but factors of design, size, shape, materials, electronics and technologies combine to impact on a speaker?s ability to accurately reproduce the original sound.

So, theoretically, you won?t find the perfect set of home theatre speakers, but our tips will help you recognise those which are technically better than others, as well as how to audition a system that is perfect for you. First, though, a lesson in sound.

A speaker comprises a cabinet and a driver assembly, elements of which include a magnet, cone, crossover circuit, voice coil and basket. Upon receiving sound as an electrical signal from the AV receiver, these elements work together to push the cone in and out. As it moves, it vibrates the surrounding air molecules causing ripples known as sound waves. These in turn vibrate our ear drums and are perceived by the brain as sound.

The frequency of the waves, or how many times they vibrate each second, determines the pitch of the sound: long, slow waves are a low pitch (bass notes and short, fast waves are a high pitch (high notes). Frequency is measured in hertz, with the slowest, lowest sound a human can hear being around 20 hertz (Hz) and the fastest, highest sound approximately 20 000 Hz (or 20 kHz). Sound goes much higher than 20 000Hz, but this is the accepted limit of adult human hearing and, indeed, the upper operating limit of most speakers. Sound waves have height too, with tall waves perceived as loud to our ears and short waves as quiet.

  The cables between your speakers and your receiver must be connected in the correct polarity – that is, with the red (or +) terminal on the receiver going to the red (or +) terminal on the corresponding speaker, and the same with the black (or -) connections (speaker cables are usually colour-coded or have a ridge or markings on one side to make the match up easy). If you don;t match the polarity at both ends your speakers are said to be out of phase, and bass response an imaging will suffer.