Is the DMM method a fairly accurate way to measure the watts output of an amplifier?

I set the meter on AC volts, connect leads to speaker terminals (w/ subwoofer still hooked up), play a sinewave burp and take that reading to determine how many watts went to the sub.

Does that sound correct? I already set the gains w/ an o-scope so I'm not trying to do that. I want to calculate how many watts actually is going to my sub

thanks

According to the How To section here, you aren't supposed to leave the speakers hooked up while measuring the voltage

as long as you did

v^2/R then you are good to go! (a/c voltage squared divided by actual resistance)

to get the R valve unhook one of the sub leads and set the dmm to the ohm setting and see what the actually impedance of JUST the sub is! if you don't unhook it you will be measuring the impedance of the amp also!

and do post your results and which amp you are using!

You need more then just a volt meter to calculate power. Watts = Voltage * Current. You can figure it with knowing your actual impedance of the speaker (at that frequency and time) and voltage or current but because a speakers impedance changes with frequency, power, etc, you need to measure voltage and current. Then you can calculate the power and resistance.

Hypothetically speaking

If my sub is 1.5 at each coil, I wire down to .75 ohm. Now with the sub hooked up I burp 50 hz. I get a DMM reading of 40 volts AC. My voltmeter showed 14.2 for the duration of the burp. Say the imedance went up to 1.3 ohm, what would the equation be?

Do I need to get a fancy clamp meter or something?

Edited June 9, 201015 yr by Typicaljawaiian

The clamp is the best way to do it, yes.

Hypothetically speaking

If my sub is 1.5 at each coil, I wire down to .75 ohm. Now with the sub hooked up I burp 50 hz. I get a DMM reading of 40 volts AC. My voltmeter showed 14.2 for the duration of the burp. Say the imedance went up to 1.3 ohm, what would the equation be?

Do I need to get a fancy clamp meter or something?

To be accurate, yes.

And even then it will be very far from being accurate. You cannot measure power without measuring distortion.

And even then it will be very far from being accurate. You cannot measure power without measuring distortion.

can't believe I forgot about distortion.

Why are you trying to measure it?

I would assume he is measuring his output just to see what he is actually getting out of his amp power wise! maybe he can turn up the gains a bit more or wire the subs to a lower impedance during a burp at say 47hz....

I would assume he is measuring his output just to see what he is actually getting out of his amp power wise! maybe he can turn up the gains a bit more or wire the subs to a lower impedance during a burp at say 47hz....

Measuring power won't let you do that. You can see everything that you need to in Voltage, no need for current.

That was exactly my point...

That was exactly my point...

I know, right after I posted I realized that I too would like to hear the answer to your question. Hopefully it still comes