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Typically measured as a percentage, THD refers to what fraction of the output is not exactly like a larger mirror image of the original. For example, 1% THD would suggest that 1 part out of every 100 contained amplification errors. Obviously, a larger amount of errors would raise the THD and the unlistenability of the sound signal.

For most listeners, 3% THD is the threshold whereby distortion becomes noticable with most types of music. At the 10% level hard clipping, which manifests itself with audible cracks and screeches usually provokes the hand to fly up and turn the knob down to something less offensive. Barely audible even with test tones, (and who listens to test tones) is distortion in the 0.05-0.20% range.

Amplifier Classifications

This is a toughie. There are two primary modes or types of audio amplification--class A and class AB. While I would love nothing better than to talk dB about these two types for the next twenty years, the gist is that class A amps are expensive, sound great, very inefficient, and impractical. And I love to design and build them. Class AB amps are inexpensive, good sounding, moderately efficient, and practical. Probably 99.9999% of all amps sold today are based on a class AB design. We shall not make mention of the dreaded economy class B amps. They cost pennies to make, sound rather nauseating and have no business in audio reproduction.

Quantity vs. Quality

Hop in a brand spankin' new Ford Mustang Cobra. Feel the raw V8 power. Feel the pressure in the small of your back when tromping on the accelerator. Fly around the curves with all four tires screaming in protest as they approach their wipeout limits. Raw, unrefined power, and a lot of it. Now, slip into a BMW M5 sedan. Enjoy the solidity and confidence at 150 mph as only a BMW can deliver. Gracefully swoosh around turns without spilling your latte. Roll down your window and snobbishly ask for Grey Poupon.

Class A amps deplete your wallet like the M5 but once the sheer quality invades the senses, anything less is suddenly slumming it. Class AB is by no means low rent. Properly executed these designs can be very musical without breaking the bank. However, all this drivel about amps does us no good if they aren't connected to anything. Since the human ear can't hear the electrons in amplifiers, hooking some wire from them to a device capable of moving air molecules seems like the best course of action.


The final or "back end" of a sound system is the actual reproducer itself. Something must move air for the human ear to perceive and interpret sound. Existing in two primary forms are driver elements, active (electrostatic) and passive. Someday, a direct connection to the brain via a neural interface might just be possible, but none are available as of yet.

The electrostatic element is usually found in large, costly speakers such as Quad or Martin-Logan. These are speakers that require high voltage charge, courtesy of your 120V wall outlet, to operate. No, they do not have internal power amplifiers within their boxes, think of it like a charge on a capacitor. The passive element is the most common and prolific element. It consists of a driver that needs no external power other than the amplifier signal. Passive sub-woofer drivers, such as those found in Vandersteens are not covered in this article.

Power Input

Speakers have limits as to how much juice can be put to their inductive coils before they physically bang against their end stops. A loud crack is heard when this happens and it's not recommended that anyone try this to any speaker you plan to listen to in the near future. Rest assured that when I spy "30W" stamped on the back of a driver, that is an absolute limit (within certain tolerances of course).

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