Ohm’s Law Question
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=18635
Printed Date: September 15, 2025 at 5:24 AM
Topic: Ohm’s Law Question
Posted By: Lebult
Subject: Ohm’s Law Question
Date Posted: September 07, 2003 at 9:42 PM
Hey,
I'm a little confused with the Ohm's Law stuff. What formula would I use to find the Wattage of my Amp? I know it pumps 1000 watts @ 4 ohms using 14.4volts, but I need to find out how many Watts it'll pump at 2 Ohms using 12 volts.
An answer wouls be great, but the formula itself woulds better. I'd like to try to figure it out myself : )
Replies:
Posted By: aggie altima
Date Posted: September 08, 2003 at 2:18 AM
Anybody can correct me if I'm wrong, but I believe that you can't use ohm's law using the input voltage to find power (watts).
Using the fact that the amp pumps 1000 watts @ 4 ohms using 14.4 volts, if you plug the voltage and resistance into the equation power=(volts^2)/ohms, the number you get is nowhere near 1000 watts, it actually comes out to 51.84.
Just remember that what the amplifier is doing is taking in the voltage from the battery, and then "amplifying" that voltage to a higher voltage. To use Ohm's Law, you should use the voltage measured at the speaker wires, not at the power wire. Again using the specs you gave and the voltage equation, the measured voltage at the speaker wires should be about 63 volts.
I hope this helps you in any way.
Posted By: xetmes
Date Posted: September 08, 2003 at 5:40 AM
its not really like there is one formula to do what you want, amplifiers are all different, and do not have the exact same relationships. you could try to say that it would be less than 2000 watts because half the impedance will usually double the power, and the lower voltage would reduce that. ohms law will not help that much because you are dealing will power. there may be a formula out there (im not sure) it may be complicate though.
Posted By: auex
Date Posted: September 08, 2003 at 8:37 AM
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Posted By: padawan
Date Posted: September 08, 2003 at 9:37 AM
Power (watts) always equals the Current X the Voltage...
P=IV or P=VI.
Posted By: DYohn
Date Posted: September 11, 2003 at 9:57 AM
What kind of amp is it? Generally a good manufacturer will supply the ratings you seek...
Posted By: xetmes
Date Posted: September 11, 2003 at 10:56 AM
padawan wrote:
Power (watts) always equals the Current X the Voltage...
P=IV or P=VI.
In a traditional sence it does, but he is talking about the output of the amp to the speakers, amplifiers are not 100% efficient, and therefore a good amount of power is lost as heat depending on the efficiency it will be different.
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