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Published on October 31, 2007

In most cases, we cannot base our buying decisions on specifications, which do not give an accurate picture of the equipment's true capabilities. Specs are necessary, but they are just a guideline.

 A great many amplifiers or head units fail to meet consumers' needs, even though they have perfect specifications. This is simply because good specifications do not mean good sound. And you cannot put any hope in those that come with bad specification, either. At one time, sound designers used to say, "My aim is to design what is best for the amp. But good or bad, I do not know as it is up to the consumers."

 Amplifier power ratings are important but not necessary in determining whether an amp will satisfy your system needs. Head-unit power ratings are notorious for being misleading. Having enough power is what most people look for in an amp for great sound. Nevertheless, power ratings do not always tell you whether an amp will offer the performance you desire.

This is because the more watts an amp can produce, the greater distortion, noise and rise in internal temperature. To cope with these distortions, manufacturers need to incorporate advanced design circuits, which, of course, come at a higher cost. As a consequence, other factors such as current capability, damping and, most importantly, design philosophy cause great sound to come into play.

 Loudspeaker efficiency is typically defined as the ratio of useful power output of a system to the power input, measuring one metre away from the speaker or one watt of power to the speaker. The lower the efficiency to the speaker, the more amp power that is applied to it.

For instance, it would take double amp watts to drive a speaker with a sensitivity of 85 decibels than it would one with 88dB. In theory, you have to double the amp watts to get a 3dB increase in volume. However, the amount of current will also increase.

When going from an 8-ohm to a 4-ohm speaker, the current will double. If the amp cannot handle that, it will overheat and short circuit. That is why the amp watts always relate to the loudspeaker when it comes to buying an amp or a pair of loudspeakers.

THD stands for total harmonic distortion, telling you something about the distortion the amp is producing at this power level. It is usually specified as a percentage: THD = 0.005 per cent means all harmonics and noise added together make up 0.005 per cent.

Therefore, amplifiers try to show the lowest THD as possible. Some amplifiers even show THD at 0.003 per cent. Again, THD is not an indicator showing how good the amplifier is. In fact, most amps have an intrinsic distortion that occurs at a near constant level for most of its power range - and then, when the amp starts to get overdriven, the distortion rises quickly.

Although total harmonic distortion is one way of measuring distortion, it can also be in forms of timing jitter and overheating of the amplifier.

 On a final note, technical specifications for audio equipment are important, but do not guarantee that the sound will satisfy your desire. Certainly, some specs are scientifically measurable, but can be sometimes misleading. In fact, sound largely involves mysterious factors, which sound engineers and designers have always tried to unlock so as to make audio products more satisfying to their customers.

By Wijit Boonchoo

The Nation

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