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I still don't get it. Sorry I don't use DMMs at all. The tutorial sorta assumes the user knows where things go. Do I disconnect the speaker - and + from the amp, and measure from those output terminals?

You can do it through the tops of the terminals (screw or allen sets) and leave the sub(s) or speakers hooked up.

And I measure from the - and + output terminals right? Because the tutorial only said using the + output. Thanks for helping this newbie.

Yes you can :)

I have a few more questions. Do I use the watt RMS numbers on the speakers or the amp?

example 1. Say I have a 75 rms x 2 ch amp, used with 100 rms speakers. Which numbers do I use?

example 2. Say I have 300 rms output on my mono amp, used with a 250 rms subwoofer. Which numbers do I use? Thanks!

jjohan35 wrote:I have a few more questions. Do I use the watt RMS numbers on the speakers or the amp?

example 1. Say I have a 75 rms x 2 ch amp, used with 100 rms speakers. Which numbers do I use?

example 2. Say I have 300 rms output on my mono amp, used with a 250 rms subwoofer. Which numbers do I use? Thanks!

Since this came up, I just want to explain speaker power handling a little bit to you. The numbers that marketing uses to quantify a speaker's "power handling" are based on a certain set of criteria. Speakers have thermal power handling and mechanical power handling. Really, your "power handling" number would be the lower of the two. But what size box are the speakers? Is the pole ventilated enough for cooling? What crossover point is being used? All of these things affect power handling.

That said, the answer to your question is obviously the marketed specs for amp output.

I would also like to add that a test tone is 100% duty cycle. Music is not. So by setting gains with a multimeter and test tones, you're selling yourself short on the available power (or even setting the amp to clip, if underrated).

So what should I do?

I ask because cargodz formula says to multiply watt rms with ohm, then square root it. Which RMS numbers do I input into the formula?

jjohan35 wrote:I have a few more questions. Do I use the watt RMS numbers on the speakers or the amp?

example 1. Say I have a 75 rms x 2 ch amp, used with 100 rms speakers. Which numbers do I use?

example 2. Say I have 300 rms output on my mono amp, used with a 250 rms subwoofer. Which numbers do I use? Thanks!

^This is a perfect example of the idea

In example #1 with a 100w rms speaker and a 75w rms amp you would use the rms of the amp as it is well within the safe range of the speakers

In example #2 with a 300w rms amp used with a 250w rms sub you would use the rms of the sub... because in this case if you were to use the amps rms you would be overpowering the sub

solacedagony wrote:That said, the answer to your question is obviously the marketed specs for amp output.

Cargodz: The gain control is for matching the max HU voltage to the amp. I would personally set the gain than use attenuation in the HU for the sub out.