# anyway to test amps output watts

luckydawg003
Copper - Posts: 63
Joined: August 30, 2007
Location: United States
Posted: September 20, 2007 at 9:36 PM / IP Logged
Just wondering if I could use a voltmeter and some formula to determine what wattage my amps are actually putting out? They are power acoustic amps. 1 is 4 channel 85W@4ohms. The other is 2ch.370W@2ohms stereo.
stevdart
Platinum - Posts: 5,816
Joined: January 24, 2004
Location: Pennsylvania, United States
Posted: September 20, 2007 at 10:15 PM / IP Logged

Formulas won't do a thing for you with this.  Neither will a voltmeter.  You have to set up a controlled testing procedure.  www.bcae1.com isn't opening tonight for me, but you'll find the procedure there.  If you actually acquire everything you need, you will find out what those amplifiers are capable of doing.  But it still won't tell you what your actual results are in the car.

Why not just lie about wattage like everybody else (including manufacturers)?  Power Acoustic is lying when they print the manual.  What's it matter about wattage?  Decibels, if anything, is what matters...if you want to know how loud something is.

I guess I might typically use about 100 watts when I play my car audio.  I also typically listen at 90 to 95 db, which is pretty loud.  It's very likely that someone else has a system that requires 500 watts to reach 95 db.  Someone else might get there with 25 watts.  It doesn't matter.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
haemphyst
Platinum - Posts: 5,053
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: September 21, 2007 at 2:05 AM / IP Logged
...or, you can open the amp, and measure the voltage rails. That voltage, is your peak to peak, multiplied by .707, squared, divided by your load, will give you an RMS value.
Example, let's say you measure 25V:
25V * .707 = 17.675
17.675 * 17.675 = 312.40
312.40 / 4 (ohms) = 78 watts, RMS
I'm not telling you to ACTUALLY open your amp, even though I am, and I won't be responsible if you fry something, yourself included.
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."
dpaton
Copper - Posts: 141
Joined: July 19, 2004
Location: United States
Posted: September 21, 2007 at 12:45 PM / IP Logged
The best way of all to measure power (on a limited budget, and assuming you have access to the gear) is with a signal generator or test tone CD, an oscilloscope, a DMM, and a big-ass dummy load.
Connect the scope and the DMM to the amp's outputs, run the amp into the dummy load, and feed it a 60Hz test tone. Crank it up until you see clipping on the scope, then back off a little, and read the AC voltage on the load. P = (v^2)/R, so square your voltage, divide by 4 or 2 or 1 (the impedance of your dummy load) and voila, power output.
Everything else will be an estimation.
There are even better ways to do the procedure, with more accuracy, but for most people, this will get you within a few watts of the correct number.
This is not a sig. This is a duck. Quack.
aznboi3644
Gold - Posts: 2,600
Joined: May 01, 2006
Location: United States
Posted: September 21, 2007 at 11:32 PM / IP Logged
how do you know where the voltage rails are??
dpaton
Copper - Posts: 141
Joined: July 19, 2004
Location: United States
Posted: September 22, 2007 at 8:58 AM / IP Logged
aznboi3644 wrote:
 how do you know where the voltage rails are??
Generally there are some big capacitors inside the amp with relatively high voltage ratings (30-90VDC). Metering near those will usually find the voltage rails.
This is not a sig. This is a duck. Quack.

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