-=Measuring Amplifier Outputs Proprely=-

[87Accord 10+ year member]

I am trying to measure the output of my amps and and getting very very low watts output. I read the way to do it was to meter the speaker outputs to get your volts AC and multiplay that by 10 then divide by your impedance. So... I get a maximum of 8 volts AC from the leads x 10 = 80volts / 4ohms = 20watts and that's divided by 2 i take it since it's going to left and right speakers. Shouldn't I be getting a considerable amount more (at 14.4dc volts since the car is running during tests) considering I am using an alpine 4 chan amp when bridged should do 100rms per channel? am I doing something wrong here?

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[keep_hope_alive Premium Member]

you have the equation wrong.

P = V^2 / R

measure your AC Volts, square that number, then divide by impedance.

how are you metering the output? note that when the amp is bridged, there is a signal on both wires (one is out of phase with the other). bridging doubles voltage at the speaker, based on the equation above, doubling voltage is quadrupling power.

i suspect your meter is having a problem measuring the bridged signal. instead, place the black lead on ground and measure AC voltage on each wire separately. they should be near equal. then add those voltages together and use that in the equation.

who told you to multiply by 10???

 

[grandam888 10+ year member]

Well first off, your not measuring rms wattage. What you will have to do is use an oscilloscope to get the gain setting where it needs to be without clipping the signal. Then you remove the oscope, and hook the dmm up to the amp. See anything above rms is useless, because of clipping, and The only way to truthfully see if your clipping is an scope.

Also, it would be a gopod idea to learn ohms law, which is were the formulas we use in car audio derive. Just google ohms law, its probably one of the most helpful tools in any situation involving electricity.