Technology has democratized the music industry in many obvious ways -- notice how every band, regardless of stature, has a MySpace page? But one of technology's more subtle effects has been to make our sound systems smaller, lighter and greener.
The special sauce: Class D amplifiers, the first real advance in speaker design in decades. These amps were once thought to be appropriate only for low-end audio devices like cellphones. But with continuing refinements they have started showing up in everything from flat panel televisions and computers to high-end sound systems.
“Imagine a light bulb in your house," said NHT audio engineer Gordon Chang. “If you turn it on all the way, it's too bright, and if you turn it off, it's too dim. Now if you turn it on and off really quickly, you can get the light to look like it's halfway between on and off." Traditional amplifiers achieve the same effect using electrical resistance, similar to a dimmer switch that controls the light. Those resistors turn valuable electricity into unwanted heat, which necessitates bulkier design. Ever wonder why your ultra-thin panel television sounds so great despite having so little real estate dedicated to audio? The Class D amplifier, which is having a massive, albeit largely unacknowledged effect on consumer audio devices, is responsible.
“The big advantage with Class D amplifiers is that they're much more efficient from an energy usage point of view than conventional Class AB amplifiers, which are what you've seen in most audio equipment up until now," said John Widder, market development manager at STMIcroelectronics, a semiconductor manufacturer. He said Class AB amps typically run at between 15 and 40 percent efficiency when playing back music, while Class D amps run at between 40 and 85 percent. And that's only part of the picture.
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