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Old 03-07-2009, 12:04 PM   #19 (permalink)
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Originally Posted by NiHaoMike View Post
Why couldn't they use TI's hybrid digital technology to improve efficiency? I have done it for home audio:
Amanda Harris: the Prius of home audio - EcoRenovator

Except in hybrid and electric cars that have high voltage electrical systems. No chip amplifier will handle 200+v (discretes can be designed for it - much to the joy of those who build loud car stereos!) so a DC/DC converter will be used to reduce it. Then the design is more like that of a home audio system. In fact, most universal input power supplies for home electronics will run from the high voltage system in a hybrid or electric car without any modifications.

I remember a friend of mine in high school who turned up the (aftermarket) stereo so loud that the lights were dimming... and then complained that gas is too expensive!
Panasonic had a few models when they were still serious about making automotive head units, which used Tripath class D amplifiers, that can be typically 90% efficient or better (compared to ~60-75% efficiency typical from A/B or darlington pair outputs) - then built an inverter type DC-DC supply into the head unit which gave the device rails at +12v and -12v (regulated, regardless of alternator voltage) - tremendously powerful as DIN head units go and would avoid the weight penalty of necessitating outboard amplifiers for truly loud sound.

In any case... there's still really nothing to chase with a regular car stereo. Before anything else I'd suggest the added weight of a big subwoofer is the most significant enemy of fuel efficiency in a car stereo because it is rare for anyone with a serious system to just drive around everywhere with it turned up. When they're not turned up loud, they don't draw much current because of the previously mentioned relationship between deciBels and wattage. If you have a "regular" stereo and are a casual efficiency hobbyist, stop worrying about the stereo right now, it's not the droid you're looking for. If you are extreme about efficiency, rip the whole thing out and wear an ipod because the weight of the parts is affecting your efficiency even when it's turned off.
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