1. ## can you test amp output in watts with a dmm?

can you test the output in watts of a amp with a digital multimeter ? if so how and what setting?

also how to you guys test speakers with a meter?

2. ## Re: can you test amp output in watts with a dmm?

not really.
you can measure voltage, but without knowing what impedance the amp is seeing you really don't have a way to calculate power.
I think the best diy way would be to put a clamp meter on the speaker wire and a volt meter on the amp's speaker outs, but even then there's no way to set the amp at the onset of clipping which is where you'd get your peak power measurement.

3. ## Re: can you test amp output in watts with a dmm?

Originally Posted by blackh8552
can you test the output in watts of a amp with a digital multimeter ? if so how and what setting?

also how to you guys test speakers with a meter?
The only real way of checking wattage is to clamp it, those cost like 80 dollars.

You can use a meter to measure the impedance of a speaker by setting it on ohms and it will tell you the resistance.

V * A = W

5. ## Re: can you test amp output in watts with a dmm?

Originally Posted by bunkerking09
The only real way of checking wattage is to clamp it, those cost like 80 dollars.

You can use a meter to measure the impedance of a speaker by setting it on ohms and it will tell you the resistance.
Are you talking about measuring impedance during a test tone current/voltage measurement? Can that even be done?

At rest DC resistance is not useful for a power calculation.

You have to know what impedance your sub presents the amp at whatever frequency is being played.

You can model it in winisd pro, but I don't know what degree of accuracy that will give either.

6. ## Re: can you test amp output in watts with a dmm?

Originally Posted by bunkerking09
The only real way of checking wattage is to clamp it, those cost like 80 dollars.

You can use a meter to measure the impedance of a speaker by setting it on ohms and it will tell you the resistance.
Only at rest with no power. You CAN NOT take an imp reading while sub is playing. Besides just getting an inaccurate reading you will most likely damage the meter and it will never read imp correctly again

7. ## Re: can you test amp output in watts with a dmm?

The DCR reading isn't accurate but it is a relative approximation.

Without buying a clamp meter or an impedance meter this is basically the only thing you can do. What you have to remember is the DCR reading is going to be usually lower than an actual impedance reading. (On a subwoofer this is typically true, a multi driver network system is a different story.) So when you do your calculation of wattage, Watt = (Volt^2)/(DC Resistance), the wattage from the calculation is going to be higher than the real wattage.

8. ## Re: can you test amp output in watts with a dmm?

I'm thinking there might be another way to figure out the impedance of the woofer.

You need three things your volt meter, 60 Hz test tone, 100 Ohm 10 Watt resistor. Radio Shack has them I think.

You are also going to need a pencil and paper. When testing you are going to need to record 3 Values; R1, Vin, Vr1.

Measure the DCR of the resistor and record it as R1. Then, wire the resistor in series with the amplifier. Play the 60 Hz test tone and slowly increase the gain until you have approximately 20 Volts at the output of the amp. Record the exact value your meter is showing as Vin. Then measure the voltage across the resistor and record it as Vr1.

To find the impedance of the driver you plug the numbers into this.

Once you have the impedance at 60 Hz you can pretty accurately calculate the wattage to the driver. Remove the resistor and hook up normally. You can then measure the voltage and plug it into W = (V^2)/D1 with D1 being the impedance found previously.

I think that should work, anyone got a reason it wouldn't? The math all work out.

Also, just a note, watch the temperature of the resistor. At 20 Volts it should be able to dissipate the wattage for short periods. 20 VDC is only 4 watts. So 10 Watts should be enough, maybe get away with a 5 Watt resistor. You could really test at 5, 10, or 15 volts. The worst that could happen is burn the resistor, they are cheap anyway. Also, some resistors can vary resistance with temperature.

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