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Does listening to heavy metal music require more battery or electrical power than other types of music, for example solo acoustic artists?

鈥� The quick answer is yes.

When an amplifier exceeds its operating capacity, a type of waveform distortion called occurs. Let鈥檚 assume that the volume is turned up to the point just before clipping kicks in 鈥� where the amplifier is pushing out its maximum voltage without distortion. This clipping point fixes the maximum output peak voltage.

An instrument with a pure tone will have a nearly sinusoidal single-frequency waveform. So the peak-to-average voltage will be 1 divided by the square root of 2, which makes 0.707. For complex music that has lots of different frequencies 鈥� particularly heavy metal 鈥� the output spends much more time at the peak voltage level, so the peak-to-average approaches 1.

Battery life is determined by the average power level, which is voltage squared. So heavy metal (and similar complex waveforms) could drain the battery nearly twice as fast as a pure tone for the same volume level.

Paul Riley, Ilkeston, Derbyshire, UK

鈥� As any heavy metal devotee will tell you, heavy metal should be listened to with the amplifier turned up to 11鈥� But that isn鈥檛 the only reason why it could use more electrical power than listening to other types of music.

Amplifiers are rated by the average power output, which is derived from the root mean square (RMS) of the alternating current voltage waveform. Because music normally has a wide dynamic range 鈥� the difference between loud and quiet sounds 鈥� the actual power consumption is likely to be much less than the quoted RMS, even when listening at full volume.

However, in recent years there has been a drive to make CDs sound louder by compressing the dynamic range, which is an idea taken from AM radio; this is the so-called 鈥渓oudness war鈥�. Allegedly the 鈥渓oudest鈥� CD created is , which would therefore use more power than a CD with a greater dynamic range.

鈥淎llegedly the 鈥榣oudest鈥� CD created was 惭别迟补濒濒颈肠补鈥檚 Death Magnetic, which would use more power鈥�

One side effect of making CDs louder in this way is that it can fatigue the auditory system. I am a long-time Metallica fan and love that album, but I can rarely listen to it all the way through. It took a while for me to work out why that is.

Richard Hind, York, UK

鈥� Heavy metal music typically involves higher and more sustained sound levels than other types. Whether this requires greater electrical power depends largely on the design of the amplifiers driving the speakers.

Class A amplifiers draw constant power from their supplies irrespective of the signal level, with any power not delivered to the speakers dissipated as heat within the equipment.

This makes them very inefficient, but they are capable of outstandingly low levels of non-linearity and distortion, and so are much loved by audiophiles.

Class B amplifiers are much more efficient because their power consumption correlates strongly with that delivered to the speakers. However, they suffer from , which results in a zero-voltage 鈥渇lat spot鈥� in the waveform and is most apparent at low signal levels. Good design can limit this to an acceptable level, but cannot eliminate it completely. Nevertheless, most high-powered audio amplifiers are of this type.

Class D amplifiers operate in a digital or switching mode, delivering power to the speakers in the form of pulses at a frequency well above the audible range. The power delivered is adjusted by varying the pulse width to produce the desired audio output and this correlates strongly with that drawn from the supply.

Efficiency is very high, and they are highly compatible with digital circuitry, so they are now the preferred type for battery-powered equipment such as cellphones and MP3 players.

So, for a class A amplifier the answer to the original question is no, but for class B or D amplifiers the answer is a qualified yes.

Tony Ellis, Porirua, New Zealand

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