DMM to read wattage of an Amp?

[osamio]

I posted a topic about my amp earlier, and the answer came back to read the output of the amp with a multimeter set to read AC voltage.. but no one gave me a clear explanation of how to do it...so a step by step kind of thing would be great.. I need to set a 1700 watt amp's gains so that it puts out a max of 900 watts with the volume all the way up...

[HHR Ed]

you need 2 meters, both true RMS meters. One with leads connected to speaker wires from the amp and set to read AC voltage.

The other will be a clamp on ammeter clamped around one of the speaker wires (plus or minus), set to read AC amperage.

Best if your meters have a peak hold function.

Play a test tone at a general frequency first like 40hz, then try 50, 60 etc.. for fun.

Take the numbers from both meters and multiply. Thats your wattage.

But why do you have to be at 900w?

[osamio]

you need 2 meters, both true RMS meters. One with leads connected to speaker wires from the amp and set to read AC voltage.

The other will be a clamp on ammeter clamped around one of the speaker wires (plus or minus), set to read AC amperage.

Best if your meters have a peak hold function.

Play a test tone at a general frequency first like 40hz, then try 50, 60 etc.. for fun.

Take the numbers from both meters and multiply. Thats your wattage.

But why do you have to be at 900w?

What should i put on the amp as a load? the actual subs? and just start with the gain tuned all the way down?

and i need 900 rms because I sold the old amp, upgraded to the 1700w amp, but it's gonna be a few paychecks before i upgrade the subs. so i have 450RMS DVC 4 ohm subs, and a 1700 watt amp. i could wire to 4 ohms, but i'd only get 250ish watts to each sub, so i'm going to wire to 1 ohm, but that's 850 to each sub, unless i set the gains right.

Edited December 24, 2010 by osamio

[HHR Ed]

OK, you can set it with the meter to be safe. That can help. But also know that ratings on woofers as well as amps are not always spot on. The woofers can usually take a bit more then rated and amps do far less power on daily music then on a test tone at max volume.

So the best tool for keeping safe levels are your ears. Just make sure if you hear anything funny or even smell burning, turn it down. Watch the bass boost because that will kill subs faster than too much wattage.

[HHR Ed]

you need 2 meters, both true RMS meters. One with leads connected to speaker wires from the amp and set to read AC voltage.

The other will be a clamp on ammeter clamped around one of the speaker wires (plus or minus), set to read AC amperage.

Best if your meters have a peak hold function.

Play a test tone at a general frequency first like 40hz, then try 50, 60 etc.. for fun.

Take the numbers from both meters and multiply. Thats your wattage.

But why do you have to be at 900w?

What should i put on the amp as a load? the actual subs? and just start with the gain tuned all the way down?

and i need 900 rms because I sold the old amp, upgraded to the 1700w amp, but it's gonna be a few paychecks before i upgrade the subs. so i have 450RMS DVC 4 ohm subs, and a 1700 watt amp. i could wire to 4 ohms, but i'd only get 250ish watts to each sub, so i'm going to wire to 1 ohm, but that's 850 to each sub, unless i set the gains right.

Yes, use the actual subs as the load.

And start with the gain anywhere, and tune accordingly. 1/4 way up would be safe

[wasntme]

if i remember, you said they were Pioneer W308D4's, i have been running one of those @ 500 rms for a year or so without a problem, still have 2 more bnib i might put on a 1000 rms amp i have here myself, so your post caught my attention

not a bad speaker either for the price range ($45-70)

[osamio]

OK, you can set it with the meter to be safe. That can help. But also know that ratings on woofers as well as amps are not always spot on. The woofers can usually take a bit more then rated and amps do far less power on daily music then on a test tone at max volume.

So the best tool for keeping safe levels are your ears. Just make sure if you hear anything funny or even smell burning, turn it down. Watch the bass boost because that will kill subs faster than too much wattage.

So if i there's no audible clipping, and no obvious damage occuring, then it should be ok to jst kind of eyeball the settings? without metering? because i don't have a clamp meter, jst a standard dmm. i suppose if i need to i could get one, if they're not too expensive.

[JJ.]

Eyes and ears are best tools dude I usually start by turning gain on amp to it's minimum turn the headunit up to the loudest I will have it then adjust the gain on the subs till they look/sound like they are not doing so well then knock it back a bit to be safe unless your silly with the gain you shouldn't damage the sub it becomes fairly obvious when your over driving the subs.

JJ

[osamio]

if i remember, you said they were Pioneer W308D4's, i have been running one of those @ 500 rms for a year or so without a problem, still have 2 more bnib i might put on a 1000 rms amp i have here myself, so your post caught my attention

not a bad speaker either for the price range ($45-70)

I've had nothing but great experiences with pioneer subs, i've seen two 308D's at 400rms each with basic pioneer highs hit 142.5 in termlab. They're pretty great for the price. and that's good to hear, i've been looking for a real world estimate of what they can handle continuously, i was hoping to push them to 450-500. I'm glad to here they'll last.

[osamio]

Eyes and ears are best tools dude I usually start by turning gain on amp to it's minimum turn the headunit up to the loudest I will have it then adjust the gain on the subs till they look/sound like they are not doing so well then knock it back a bit to be safe unless your silly with the gain you shouldn't damage the sub it becomes fairly obvious when your over driving the subs.

JJ

That's exactly what I was planning to do, just never done it. Only thing i'm worried about is long-term damage.. Is there a chance they'll appear to be fine, but that after a few hours or even a few days of daily they might blow? or is it fairly obvious right away if they'll hold up or not?