using a dmm under 4 ohm load my amp does 45 volts a/c.

[MONSONwarrior Premium Member]

So about a year and a half ago my father passed away, I'm only 17 btw, and he left me a giant Snap-On tool chest full of tools, I know pretty well how to use everything in there but a couple days ago I was sorting through one of the drawers and found a little carrying case with a DMM in it. After I read this thread I got to thinking about it and went out to investigate it some more, I found that it's a Fluke 36 True RMS Clamp Meter. Now from what I've read I can get a rough estimate on the power I'm seeing so I was wondering how to do that with this meter? I put the leads on the speaker outs of my amp and it didn't read anything. I had it set on AC amps and it has peak hold and everything. I just want to measure what I'm getting when I set the amp by the RMS chart and equation you guys gave in here.

Any ideas or help?

 

[roarzorz 10+ year member]

If you don't know what the amp is putting out you can use the DC amperage that the amp is consuming (that's what the DC clamp is for) along with the efficiency and the AC voltage out to the speakers and a bit of math work and you can get a closely rough idea of how much power the amp is putting out. You still wont be able to tell if you're clipping though. Clamping the AC output on the amp isn't going to tell you any more then actually testing w/a DMM what the ACV is.

And how do you plan on knowing what the exact efficiency of the amplifier is?

 

[smgreen20 10+ year member]

You do not need to know what the exact freq of the amp is. Ohms law for this application could care less what the freq is. It all has to do with amperage, volts and resistance, not freq. That's another reason why you take the readings w/o a physical load presented to the amp.

 

[roarzorz 10+ year member]

You didn't answer my question. How are you gonna calculate power based off amplifier efficiency when you don't know what the amplifier's efficiency is? You can't.

You do not need to know what the exact freq of the amp is. Ohms law for this application could care less what the freq is. It all has to do with amperage, volts and resistance, not freq. That's another reason why you take the readings w/o a physical load presented to the amp.

So how are going to calculate using resistance w/o a physical load (aka resistance) on the amplfier? It's far past obvious that you've never actually done any real world in car testing with car audio products. You can't calculate using resistance cause resistance is not a constant. In real world conditions a subwoofer presents a reactive load. That reactive load changes with frequency.

Ohm's Law requires knowing two of the three variables to calculate the third. AC voltage, AC current, and resistance. Without clamping the AC current output of the amplifier you only know one of those variables. You must clamp the AC current output of the amplifier before you can calculate the reactive resistance of the subwoofer.

 

[Haunz 10+ year member]

The difference from 50hz to 60hz is extremely marginal at best.

That may be so but when you have a non RMS meter that is calibated to 60hz and you are picking up harmonics of the 50hz test tone (at 150hz ect) because the amp is running into distortion it's going to throw your reading way out of wack, which is likley what happened to the OP...

That's another reason why you take the readings w/o a physical load presented to the amp.

WAT?

Ohm's Law requires knowing two of the three variables to calculate the third. AC voltage, AC current, and resistance. Without clamping the AC current output of the amplifier you only know one of those variables. You must clamp the AC current output of the amplifier before you can calculate the reactive resistance of the subwoofer.

Actually even if you clamp the current output into a sub, you still don't know what the real power output is, or the reactive resistance... Unless you know the inductance and capacitance of the coil and can account for power factor you are only measuring the apparent power...

Any real test of an amplifier's output should be using a non-inductive dummy load.. and in such a case having a clamp isn't totally necassary so long as you at least have a true RMS DMM.. you should also have a scope or a test program like speakerworkshop to account for THD + N.

 

[DidUHearThat? 10+ year member]

Jesus! No. No, and NO! You can't test the output of an amplifier in any of the ways listed in this thread. Obviously none of you have ever done this.

1)Testing the input current of an amp tells you NOTHING about it's output.

2)Testing the output into a reactive load tells you NOTHING about it's output

3)Testing the output without knowing it's THD tells you NOTHING about it's output

4)Performing any amp testing that cannot be compared to other amp testing methods tells you NOTHING about it's output.

Using random freq tones, into reactive loads, without knowing the THD is a meaningless number.

You need all of these to test an amplifier output:

1)Oscolliscope

2)Reference tone generator

3)True RMS meter

4)Reference Dummy load

5)Reference Amplifier

6)Knowledge and experience to compare to other amp testing methods.

If you use a different amp testing method than what the premium manufactures use (like Alpine, JBL, etc) then your number is meaningless. When Crown says their amp puts out 100 watts @ 4 ohms, that is true, and if you have the right gear (and know how to use it) you can verify that. Crown, JBL, Alpine, etc will tell you exactly how they got that number. When "BOSS" audio or PA say that, they're lying. Different amp testing method = meaningless number.

 

[stanky1219]

Jesus! No. No, and NO! You can't test the output of an amplifier in any of the ways listed in this thread. Obviously none of you have ever done this.
1)Testing the input current of an amp tells you NOTHING about it's output.

2)Testing the output into a reactive load tells you NOTHING about it's output

3)Testing the output without knowing it's THD tells you NOTHING about it's output

4)Performing any amp testing that cannot be compared to other amp testing methods tells you NOTHING about it's output.

Using random freq tones, into reactive loads, without knowing the THD is a meaningless number.

You need all of these to test an amplifier output:

1)Oscolliscope

2)Reference tone generator

3)True RMS meter

4)Reference Dummy load

5)Reference Amplifier

6)Knowledge and experience to compare to other amp testing methods.

If you use a different amp testing method than what the premium manufactures use (like Alpine, JBL, etc) then your number is meaningless. When Crown says their amp puts out 100 watts @ 4 ohms, that is true, and if you have the right gear (and know how to use it) you can verify that. Crown, JBL, Alpine, etc will tell you exactly how they got that number. When "BOSS" audio or PA say that, they're lying. Different amp testing method = meaningless number.

alpine is shit. my 150 watt mtx kills my uncles mrp-450.

 

[DidUHearThat? 10+ year member]

alpine is shit. my 150 watt mtx kills my uncles mrp-450.

WTF does that even mean?

Did you even understand what I wrote? Your opinion of Alpine is irrelevant, what they claim for their output is true. Kenwood is another. It's not about brand or "kills" (what ever that means). It's about testing method.

They have, you don't.

 

[roarzorz 10+ year member]

That may be so but when you have a non RMS meter that is calibated to 60hz and you are picking up harmonics of the 50hz test tone (at 150hz ect) because the amp is running into distortion it's going to throw your reading way out of wack, which is likley what happened to the OP...

Agreed, but nobody should be using a meter that isn't true rms.

WAT?

I agreed with this too. That guy is just babbling in circles.

Actually even if you clamp the current output into a sub, you still don't know what the real power output is, or the reactive resistance... Unless you know the inductance and capacitance of the coil and can account for power factor you are only measuring the apparent power...

Any real test of an amplifier's output should be using a non-inductive dummy load.. and in such a case having a clamp isn't totally necassary so long as you at least have a true RMS DMM.. you should also have a scope or a test program like speakerworkshop to account for THD + N.

We're splitting two different ways here. You're talking bench testing & I'm talking in-car testing. There is only one way to test an amplifier in a car. This is what I call "real world power". Bench testing is all fine & dandy to see an amplifier's capability in perfect conditions but this isn't the way these amplifier's are used on a daily basis. We don't listen to dummy resistors. We listen to speakers/subwoofers (aka reactive loads) and different amplifier designs work completely different in these scenarios. That's something you won't see on a bench.

 

[roarzorz 10+ year member]

Jesus! No. No, and NO! You can't test the output of an amplifier in any of the ways listed in this thread. Obviously none of you have ever done this.
1)Testing the input current of an amp tells you NOTHING about it's output.

2)Testing the output into a reactive load tells you NOTHING about it's output

3)Testing the output without knowing it's THD tells you NOTHING about it's output

4)Performing any amp testing that cannot be compared to other amp testing methods tells you NOTHING about it's output.

Using random freq tones, into reactive loads, without knowing the THD is a meaningless number.

You need all of these to test an amplifier output:

1)Oscolliscope

2)Reference tone generator

3)True RMS meter

4)Reference Dummy load

5)Reference Amplifier

6)Knowledge and experience to compare to other amp testing methods.

If you use a different amp testing method than what the premium manufactures use (like Alpine, JBL, etc) then your number is meaningless. When Crown says their amp puts out 100 watts @ 4 ohms, that is true, and if you have the right gear (and know how to use it) you can verify that. Crown, JBL, Alpine, etc will tell you exactly how they got that number. When "BOSS" audio or PA say that, they're lying. Different amp testing method = meaningless number.

Same as as said before. There is only one way to test an amplifier in a car. This is what I call "real world power". Bench testing is all fine & dandy to see an amplifier's capability in perfect conditions but this isn't the way these amplifier's are used on a daily basis. We don't listen to dummy resistors. We listen to speakers/subwoofers (aka reactive loads) and different amplifier designs work completely different in these scenarios. That's something you won't see on a bench.

You need all of these to test an amplifier output:

1)Oscolliscope

2)Reference tone generator

3)True RMS meter

4)Reference Dummy load

5)Reference Amplifier

6)Knowledge and experience to compare to other amp testing methods.

My amplifiers don't play into a dummy load with a signal from a tone generator daily. Then play music from my head unit into my subwoofers. I'd rather know what my amplifier can do sitting in my vehicle instead of sitting on a test bench.

 

[roarzorz 10+ year member]

If you use a different amp testing method than what the premium manufactures use (like Alpine, JBL, etc) then your number is meaningless.

This made me lol a lot. I'm surprised you not didn't mention jay el audioz.

 

[DidUHearThat? 10+ year member]

Same as as said before. There is only one way to test an amplifier in a car. This is what I call "real world power". Bench testing is all fine & dandy to see an amplifier's capability in perfect conditions but this isn't the way these amplifier's are used on a daily basis. We don't listen to dummy resistors. We listen to speakers/subwoofers (aka reactive loads) and different amplifier designs work completely different in these scenarios. That's something you won't see on a bench.My amplifiers don't play into a dummy load with a signal from a tone generator daily. Then play music from my head unit into my subwoofers. I'd rather know what my amplifier can do sitting in my vehicle instead of sitting on a test bench.

Then why are you using a meter? Just use your ears. They are the only accurate measurement tool in the car. Using a meter on a reactive load is a meaningless test. You learn nothing from the number on the display. It cannot be compared to any other amp, load or calculation.

 

[DidUHearThat? 10+ year member]

This made me lol a lot. I'm surprised you not didn't mention jay el audioz.

What? Engrish much?

 

[stanky1219]

WTF does that even mean?
Did you even understand what I wrote? Your opinion of Alpine is irrelevant, what they claim for their output is true. Kenwood is another. It's not about brand or "kills" (what ever that means). It's about testing method.

They have, you don't.

buddy,i dont know where you are getting your info but kenwood makes terrible amps these days. nowhere near rated power (my uncle has a x40 and it cant compare to my punch 200a4 , we compared them in vehicle 70x4 vs 25x4 and the punch came out on top). and by kills , i mean same sub , different amps , alpine vs mtx , mtx shakes every mirror , alpine shakes nothing but the woofer cone. now this alpine says it puts out 400 watts , and my mtx says it puts out 150. the results are visible and audible. in terms of power output my mtx would kill that alpine. my final conclusion low end alpine and even high end kenwoods ARE NOT AS POWERFUL AS THE STICKER SAYS!!!

 

[roarzorz 10+ year member]

Then why are you using a meter? Just use your ears. They are the only accurate measurement tool in the car. Using a meter on a reactive load is a meaningless test. You learn nothing from the number on the display. It cannot be compared to any other amp, load or calculation.

You're confusing opinion with fact. The fact is in car testing is only meaningless in your opinion. In my opinion in-car results are all that matters. Bench ratings are only good for advertisement purposes. "Look at how much power this amplifier made on our test bench under perfect climate controlled circumstances with zero voltage drop from our power supply and zero impedance rise from our dummy load even though your vehicle will never replicate any of these circumstances and you'll never actually see this amount of power out of this amplifier in your setup "

Years ago I did a head to head in car test between three different amplifiers. All were class D monoblocks that made power @ 1ohm. They were bench rated 2000w, 1500w, and 1000w. Those ratings would lead you to believe the 2000w amp is the most powerful. However, in this test the 2000w amplifier made the least power on a reactive load head to head with the other amps. It would have been nice to know that particular amp wasn't going to do well on a reactive load instead of me having to spend my money buying and time testing all three amps to see which worked best. Certainly I don't need some clamp meters to tell me which sounds best in my setup as my ears work fine but these meters give the concrete factual proof of results instead of just saying "this one sounded louder".

On another note Spl competitions are moving towards clamped power classes. Those clamped power #s mean everything to us and there is only one way to clamp power in a vehicle which is what this thread was about.