More speaker physics :-)


Silver Member
Username: Skies

Courtenay, British Colu... Canada

Post Number: 509
Registered: Aug-05
Okay, some more fun :P
In car audio, everything is more or less 12-14.4V, and increasing the current results in more watts. Basically, the more watts, the more current your getting. Right?

But, I was thinking... When you put a DMM to your Speaker +/- you get more than 12V. Sometimes 30-50V. Now, with a higher voltage you would need a lower current to reach same wattage. Would that not create a less effective power, so to speak? Because its the CURRENT that makes the speaker move, not the voltage?

Also, same topic, when hooking up a car subwoofer(or even home, for that matter) in the house you get 120V don't you, so again you wouldn't need very much current at all? So again, you get less current..

There was another thing I wanted to ask, but it has slipped my mind :-(

Anyways, thanks in advance!

Gold Member
Username: Nd4spd18

Southeast PA

Post Number: 1289
Registered: Jul-06
Ok, here we go:

Do you know the difference between AC and DC current? Read this:

AC is what you get on the speaker terminals of your amp, and out of your wall outlet. DC is what you get from your car battery/alternator.

Current is the rate of electron flow, and it is measured in amps. Volts are what "pushes" amps. Amps are what is available to be pushed. Watts are a measure of voltage and amperage combined. Go to and read the first few pages, it will explain this better.

Speakers work on AC current, the reversal of polarity at a variable rate is what makes the speaker cone move in and out. For a better explanation of that, read this:

And some people think car audio is simple

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11798
Registered: Dec-03
cars are goofy things.
the alternator produces AC voltage. the voltage regulator converts that to 12VDC and stablizes it for the electrical devices in the car.
you can only draw as much current with these devices, including the stereo system, as the alternator can produce. It's the heart of your charging system.

Now your stereo amplifier has a multi-rail PWM power supply. It takes 12VDC input, and converts that to several voltages for the amplifier. 5VDC for the electronics, 24V rails for the output stage, etc.. the power supply is actually capable of producing up to 3 or more times the power output of the amp's RMS output rating, inorder to handle transient demands.
The output stage of the amplifier though, is high voltage, low current AC, because it has to reverse directions with every sine wave sent to the speaker, with voltage representing amplitude, and time representing frequency.

In short, your understanding was a bit off target, and very oversimplified. has a lot of valuable information on these topics though.

for home audio, you're usually dealing with 115 or 230VAC and usually about a 30A circuit, and while this does make for a lot of potential power, the amplifier's power supply is still the same.. it converts the power to AC and DC as needed, in amplitudes it can use more efficiently.

Platinum Member
Username: Glasswolf

Wisteria, Lane USA

Post Number: 11799
Registered: Dec-03
on a side note, this gets into why the power supply of an amplifier is so vital to it's quality and overall performance
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