How to Test a Car Amplifier
How do you test the power output of your car amplifier? It’s simple with the help of a digital voltmeter. Just make sure your amplifier is connected to some speakers and a head unit so you can test the output. The voltmeter tests the amount of voltage that the amplifier is feeding your subwoofers. The voltage can be converted to wattage using standard physics conversions.
First connect the volt meter to the speaker outputs on the amplifier. With the volt meter set to AC voltage, turn up the volume on your head unit and watch as the volt reading rises. The meter is gauging the amount of power that is going to the subwoofers. Wait until the voltage meter stops at the peak power for a few seconds. This is the peak voltage rating.
Once you have the peak voltage rating, enter it into a calculator and multiply the number by itself. For example, if your voltage rating was 30, you would multiply it by 30 to get a total of 900. Now divide this amount by the subwoofer’s ohm load (or impedance). The subwoofer’s impedance rating can usually be found on the subwoofer and is measured in ohms. For example, if you were using a 2 ohm subwoofer, you would divide your total by 2 to get the peak power rating. In our example our total was 900, so dividing this number by 2 would put us at 450 watts of peak power. This means that the amplifier puts out a total maximum power of 450 watts. The RMS is approximately half of this number. So in our example you would divide 450 by 2 to get 225 watts of continuous RMS power. This means your car amplifier can provide your subwoofers with 225 watts on a continual basis. In order to experience optimal performance, you should find subwoofers that can handle around 225 watts of RMS power.
Below are the calculations for your reference:
(AC Voltage x AC Voltage) / Impedance of the Subwoofer = Peak Power produced by the amplifier
Peak Power / 2 = RMS Power produced by amplifier