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Old 01-27-2007, 10:31 AM   #8
JackG
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Join Date: Mar 2005
Location: South Carolina
Posts: 530
Quote:
Originally Posted by MNBoxster
Hi,

The issue about matching impedence is really one of preventing overheating, or local hotspots, in the Amplifier. This was especially true with Tube driven ones. But, modern solid state IC amplifiers do not use matched impedances at all, contrary to myth.

The driver amplifier has a low output impedance such as < 0.1 Ω and the loudspeaker usually has an input impedance of 4, 8, or 16 Ω - many times larger.

Happy Motoring!... Jim'99
The problem with the new amps is not so much impedance matching (as it was in older tube amps), but the specs of the final output devices (or ICs).

It's basic ohms law. Current is voltage divided by resistance (I=E/R). Power is voltage times current (P=ExI). An audio amp will attempt to send the same voltage out to the speaker regardless of the impedance (resistance) of the speaker attached. If you cut the impedance in half, at the same voltage, you double the current flow. Since P=ExI, you've doubled the power. That's why most amps that are rated to drive 2 ohms show they deliver nearly double the power at 2 ohms than at 4 ohms.

The problem is that if the amp is not rated to drive 2 ohms, the final output stages of the amplifier will not be able to deliver that much current. It's internal power supply can also be a current limiting factor.

The results are overloaded electronic devices in the amp, which results in heat and device failure. Also, while the amp is still working, it will be clipping (as it runs into it's own capability ceiling) and that's the worst thing you can do to a speaker. You will damage a speaker much quicker by clipping the amplifier than by overpowering the speaker with clean power. Speaker voice coils *hate* DC current, and that's what a clipped signal is. Clean audio power is essentially AC current that is changing continously to match the vibrations of the sound of the music it represents.

Whew! Enough of that crap. I'm going to drive the Box.
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