How do amplifiers work?

Here's how I look at it: electricity is generated by converting one form of stored energy into another. Moving water, wind, or steam made from fuel spin turbines which are like big reverse electric motors. In your home there are wall outlets. The power company regulates the energy available from them at a set standard. Using standards makes it possible to reliably run devices connected to the system.

Until you connect something that uses electricity (a load) to the outlet, nothing happens, no energy flows. Audio gear operates with its own set of standards. This allows different brands to work together. By itself, the amplifier is both a energy converter and a storage device. The amplifier has a missing part which is completed when you connect your speakers. The speakers motor electrical energy into moving air. How much air? That all depends on what qualities you want your music to have.

A CD player converts a set of digital instructions into a regulated energy flow. Likewise, a phonograph converts a set of molded plastic instructions into an energy flow. The preamplifier converts the flow into a form that the power amplifier can use. The power amplifier converts the flow into a form the speakers can use.

How well all these conversions take place is a matter of choice. The choices designers make result in performance limits. The limits of performance are conveyed to you as specifications. For example, when the conversion is out of whack (distortion) by 1% over a certain range of instructions an amplifier is said to have the capability to steadily produce so much power. Increase the distortion you're willing to accept and the amplifier can have a higher power rating. Limit the range of instructions sent to it and again the rating looks better. Don't be fooled. The important thing to remember about the power rating is that it is a description of the amp's capability, not a description of its moment to moment operating condition. An amp rated for 100 watts continuous may indeed momentarily output one or 300 watts.

An amp's capability derives from how well it converts, stores and regulates energy, how it controls heat, how well it converts its instructions, and the length of time it can be expected to do these things before it fails. Bigger is not always better. If you want to amplify music so 50,000 people in a stadium can hear it or if you want to blast your stereo at home you'll need different amplifiers to suit each application. Regardless of its specs, how subjectively well the amp fits your application is a matter of perception.

Wet, for some insight into how it all works, we'll have to talk about another rating, the efficiency of the speakers. The standard efficiency rating is expressed as a certain sound pressure level measured one meter away that is produced using one watt. Loudness is measured in decibels (dB). Say your speaker is rated at 87 dB. For every 3 dB increase in loudness the watts have to double. So at one meter, in this example a pressure of 90 dB takes 2 watts, 93 takes 4, 96 takes 8, 99 takes 16, 102 takes 32, 105 takes 64 and so on. However the efficiency ratings assigned to speakers are often overly optimistic, so as with everything audio take them with a grain of salt. The other interesting thing about the dB scale of loudness is that it takes an increase of 10 dB to make something twice as loud. To get a handle on how loud is loud search the net for a chart of typical sounds. Don't quote me but an idling car might be 50 dB, going 70 mph might produce 80 dB inside the car, a jet airplane at 5000 feet 95 dB and standing beside a jackhammer 120 dB.

Some speaker makers provide the maximum sound pressure they believe their units can reliably reproduce. 115 dB would be a pretty good rating as that's terrifyingly loud. In our example, figure out for yourself how much power that's going to take.

One of the wild cards in the loudness scenario is how the speakers use power at different frequencies. Heavy bass notes indeed take more juice than brushing cymbals. Some speakers are able to extract more potency from the amp at lower frequencies. Which ones? Read reviews or listen to them. Amps and speakers loafing along under heavy load can get louder and do it sounding cleanly. Straining combos have nothing left to give but more distortion.

One thing to look for is physical weight. If one amp has a rating of 100 watts per channel and weighs 50 lbs. and another a rating of 150 watts but weighs 25 lbs. there's a high liklihood the heavier one will supply more peak punch than the lighter one. Power supplies are heavy! Put another way, one thing to ask yourself while shopping is: "How much of a boat anchor am I willing to live with?"

Sorry but there's no simple way to answer the question: "How potent is my amp?" Numbers only tell a part of the story. Don't expect them to replace your own judgement and sensibility. The specs help but when it's all said and done YOU are the ultimate measuring device. Find your own comfort level. Once you can say this amp works for me and I'm happy with it, you're there. If it hurts when Johnny down the block says his amp does 1000 watt peaks, you're not there.