Car Audio Message Forum - CarStereo.com

Welcome to CarStereo.com the Internet Guide to Car Audio

MY ACCOUNT

SonicElectronix.com - 1-877-BUY-SONIC

Up to $30.00 in FREE custom install kits on select car stereos. Largest selection online, great prices, Daily Deals and FREE shipping on most products. We are an authorized dealer for Infinity, JBL, JVC, Kicker, MTX, Vibe, RE Audio and others.

Car Audio Black Friday Sales!

Car Stereo Message Forums > General Discussion > calculating box rise and true power

Go Back

Pages (2): [1] 2 Next

Author

Thread

sicaudio
Senior Member

calculating box rise and true power

Please perform all tests with caution!!! make sure you are using the right settings on your meters and that your leads are plugged into the correct places, and use common sense when playing with electricity. I take no responsibility for your actions in performing these tests. You have been warned!!!

Ok let's have a little talk about true system power vs. rated system power.

First off, ALL amplifiers have some sort of rating printed on them that will give you some kind of idea (realistically or not) of the output power of the amplifier, but let's have a look at how this rating is brought to attention. Some manufacturers actually test the output and some go by a computer generated "theory" of the output, some amplifiers internally ramp up the 12v DC input before the current is drawn by the PCB inside, while others do not, some amps are also rated at voltages other than 12.6v, some amplifiers can take an input voltage of up to 24v, and all of this can effect the true power, as can charging system, cable choice's, bad vehicle grounds and battery malfunctions.

So let's look at how you can easily figure your true system output within your specific vehicle and setup, by figuring your box impedance rise and true amplifier output thru a few simple tests and a little math.

Your going to need an AC/DC clamp meter and a second digital multimeter, and a signal generator or test cd with 50hz sine wave.

For the "Clamp test" to find true amplifier output you will need to set your clamp to AC amperage and clamp it on the negative wire going from the amplifier to the speaker, and place the DMM on AC volts and use the peak and hold setting if available. This test will need to be repeated for each amplifier that has a separate speaker connected, strapped amps can be measured off the slave amplifier side running to the speakers.

You will need to measure the AC voltage output going to each of your subs or if they are bridged just the wires going into the amp. Set the 50hz tone, slowly roll into the volume and watch the meter for the peak, also listen for clipping and as SUBfather said to me once "listen for smells", at the same time you get the peak AC voltage you will need to find the peak AC current to the speakers as well.

Here is an example to help with the math a little bit...
You clamp your wire for peak AC current and get 38.6 amps of current You probe the + & - speaker wires and get 61.7 volts

Next you would take the 61.7 volts and multiply the 38.6 by it to find your MAX power which would be 2381 watts. This is your True system power within your specific vehicle, box and set up. These very numbers could change if you transplanted the entire system into a different vehicle and will need to be tested again, or if you change alternators, batteries or even power cable sizes.

Next to find out your box's impedance rise you would use the same numbers you got in the clamp test before but this time we are going to divide the voltage 61.7 by the amperage 38.6 which would be 1.59 ohms

So if you were to have a nominal or starting resistance of .5 ohms that you wired the speakers to, you would have a box impedance rise of 1.09 ohms, but would have an overall reactive load of 1.59 ohms

Now your ready for any competition with your setup, you know your true system power output to get classified correctly, you know your active impedance that your amplifiers are really seeing, and now you know better than to try connecting speakers to power amplifiers while they are on and running, those voltages at those amperage's could easily injure and even kill you.

the only difference in this method and my method is that i do a more accurate test by using a true RMS clamp and DMM meter and no peak hold... which requires 2 people to help record the numbers.

Sic.