comparing amps at different voltages?

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=61073
Printed Date: May 13, 2025 at 4:24 AM

Topic: comparing amps at different voltages?

Posted By: luckydevil
Subject: comparing amps at different voltages?
Date Posted: August 10, 2005 at 12:35 PM

How do you go about comparing the rms wattage output of two different amps whose specs list two different voltages that they were tested at? I searched and didn't find anything and I also looked over all the Ohm's Law info and just couldn't figure it out for the life of me.

For example which of these would have a higher rms output at 12.9v?

US Acoustics USX2050: 50w x 2 @4ohms+12.9v, 80w x 2 @2ohms+12.9v

Clarion APA2160: 80w x 2 @4ohms+14.4v, 125w x 2 @2ohms+14.4v

Thanks.

Replies:

Posted By: luckydevil
Date Posted: August 10, 2005 at 12:36 PM

I know there will probably not even be an audible difference between the two, but I am just curious about how to do this problem.

Posted By: tcss
Date Posted: August 10, 2005 at 1:35 PM

This usually is comparing your car with the engine not running and the amps running on just the battery ( 12 volts ) versis the car running and the alternator spinning ( 14.4 volts )

Posted By: boulderguy
Date Posted: August 10, 2005 at 2:35 PM

The simple approach would be divide watts by voltage to get watts per volt, then multiply by new voltage to get new watts @ that voltage. This assumes everything is linear, which I think it would be. At that rate, your US acoustics amp would put out 56wpc @ 14.4v.

Posted By: haemphyst
Date Posted: August 11, 2005 at 12:01 AM

Also, the higher voltage of a running car will almost always provide a higher output voltage. Most amplifier power supplies are unregulated, so this makes perfect sense.

A regulated power supply will always put out the same power, whether the car is running or not.

The watts per volt theorem is a GRAND oversimplification, because as the voltage supply increases, the amp (current, not amplifier) demand will increase as well... A given amplifier will not always pull 10 amps, no matter the input voltage - it (the current) will increase as the voltage does... Most amplifiers will run more efficiently when allowed more input wattage as well, so the chances of getting only 56 watts is pretty low... it'll be higher than that.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Posted By: luckydevil
Date Posted: August 11, 2005 at 5:54 AM

good info. thanks guys!