Calculating Amp Output with a DMM and ohm's law?

[skylineTT 10+ year member]

sooo i was wondering if it is correct for me to calculate power this way.. i know impedance rise should be involved and stuff, but the sub measures 1.3ohms final and the amp reads 48.5v on a 30hz test tone from the speaker outs so is it correct to think that it is doing around 1200 after box rise?

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[thevic24 5,000+ posts]

If you can put an amp probe on the amp while you are testing it, along with the meter for voltage, then you will get your box rise and power output.

 

[skylineTT 10+ year member]

amp probe ey? as in an ammeter and a voltage meter working at the same time to measure amperage and voltage to say that P=I*V?

 

[thevic24 5,000+ posts]

10-4

 

[Kangaroux 5,000+ posts]

In order to properly calculate the amp's output you need at least 2 meters...One being just a typical multi meter to measure the AC volts on the amp and a true RMS clamp meter clamped around the positive wires to measure amps. Alternatively you can use a 3rd meter to measure the voltage going into the amplifier to see what it's doing at what voltage.

 

[skylineTT 10+ year member]

hmm, looks like i need to find an ammeter or rms clamp meter. they have them on amazon but ehh, ill look locally

 

[keep_hope_alive Premium Member]

AC clamp ammeters are pretty inexpensive and a useful tool for this application.

30Hz is probably around the Fs of the driver, so your impedance is not at a nominal value, but much higher.

use a test tone that is at least 2-3x of the driver Fs.

P = V^2 / R (or Z)

how did you "measure" final impedance? did you measure DC resistance?

48.5V into 1.3 ohms is 1800W.

another thing to consider is if your DMM is a True RMS reading, or if you are clipping. clipping will quickly increase the voltage reading of the DMM. that is why I use an oscilloscope when trying to achieve rated output. additionally, some meters are designed to read 50-60Hz VAC which can lead to false results when reading other frequencies. you need to consult the manual/specs for your DMM to know what it can and can't do, and what the tolerances are.