Don’t Be Fooled By The Power “Ranting” On Music Systems

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

13 November 2005

When a music system has a label that reads, say, 200W; is that the maximum power OUTPUT of the amplifier or is it the power HANDLING capacity of the speakers? If a hi-fi labelled 100W is fitted with 200W speakers, will it sound louder? Further, is a 1,000W machine twice as loud as a 500W one?

To answer these questions, we need to understand the relationship between power and music loudness. But first, let us clear the air regarding the labels on music systems. Most machines (so called boom-boxes) in the market today quote something known as “Peak Music Power Output”, or PMPO. The figures quoted are usually many hundreds (or even thousands) of watts.

PMPO is a completely meaningless quantity that is determined by multiplying the real power by a factor K. The value of K depends on various other quantities; the most important being the height of the marketing director and the size of paper the figure will be printed on!

Think about it: If the boom-box is going to produce, say, 2,500watts, then every time you switch it on, the lights in your house would dim momentarily. And even if it the system was 100 percent efficient in utilising power, your monthly electricity bill would be higher than the price of the hi-fi! 2,500W is equal to the consumption of a water heater and an iron box combined!

The truth is that, in acoustic engineering, there is no quantity known as PMPO. It is a creation of marketing gurus to make their products look louder (!) than they actually are. Do you see the contradiction? “Look” is to eyes, and “louder” is to ears. Indeed, some engineers insist that PMPO is a power ranting – not a rating!

So, can one then tell if a 2,000W system will sound louder than a 1,000W one? NO. And does 2,000W sound “better” than 1,000W? Not necessarily – if it does sound better the reason will have nothing to with the power ranting.

The true power is determined by multiplying the average voltage at the speaker terminals by the average current when the amplifier is at maximum level. This is sometimes called the continuous power or RMS power. RMS stands for Root Means Square. It is simply an average quantity.

Some of the loudest music systems available (such those used in out-door concerts and religious crusades) can produce a few hundred watts. If you doubt this, visit any shop that sells professional sound equipment and see for your self.

There is another complication: is the power written on the system the output from the amplifier or is it the maximum handling capacity of the speakers? Which of the two quantities determines how loud the sound is going to be? That is a story for another day.

For now, if you want to know the true power output a boom-box, check the power consumption written at the back of the machine. Then divide that figure by five. For example, if consumes 100W from the socket, it is unlikely to give out more than 20W. And always remember, no machine (musical or otherwise) can produce more power than it consumes. That is a simple fact of life.