is there any way to measure the output power of a car audio amp?

thanks!

 

ummm i guess an electicians shop could help you..

 

just wondering if i could do it myself

 

there are formulas to finding out theorectical numbers but u i dunno them.... i would say maybe, maybe you could you a decent multimeter but i would rick having one explode when you hook it into ur amp

 

There is NO easy ways to do this with ANY accuracy. There are some formulas out there online that will have you measuring the output voltage, but they're NOT right. Don't use them.......

 

get a decent multimeter for $30.

Turn the HU volume to where you have your gains set at, take a reading across the speaker output terminals. Be sure the multimeter is set to read Volts AC.

V^2/R=W

This will give you a wattage reading of what you are sending to your sub.

To test an amp properly you need a DC power supply, bank of resistors, and an oscilliscope.

Nick

 

uh i just bought mah dad a multi meter for xmas and it was $60.... the 30 ones look cheap

 

i have a dc power supply and a crap load of resistors, no oscilliscope though lol.

thanks for the reply

 

BS.!.! This will tell you NOTHING.
1> If your not using a true RMS meter any reading you get for a frequency other then 60Hz WILL BE WRONG. A good True RMS meter WILL run more then $30.00 or even $60.00.

2> What are you going to use for R in your equation? 4 ohms? If so you would be wrong. A speaker is a reactive load. 4 ohms is it's DC resistance and has NOTHING to do with it's impedance at any given frequency (well, almost nothing).

So when you do your math the two numbers your using are meaningless. At any frequency other then 60Hz your voltage reading will be off. Even if you use a 60Hz test tone you don't know what the speaker impedance is. Is R 3.4 ohms, 30.6 ohms, or 25 ohms?

This is a little closer. The bugs here are you would need to use high wattage resistors. Allot of high wattage resistors are wire wound and inductive. So you have to make sore they're non-inductive and high quality 5% or better for the math to be close. I would also like to see a precision low resistance high power shunt so you can "see" and measure peak current as well as voltage. Use a two channel scope, one channel on voltage across the load and the other across the shunt (like 0.001 ohm or better).
Just keep in mind that doing it this way you don't have an accurate way to measure %THD. The lower %THD these amps are rated at are going to be missed using a scope. You're just not going to be able to see it on a scope.

What ever number you come up with at home is probably not going to mesh with any numbers the manufacturer is getting. And if they do mesh it's just dumb luck.
Even a blind squirrel can find a nut from time to time.

Posted by ME.

 

Measuring the amp's voltage when driving a 4 ohm dummy load will give you a rough approximation, but not many people have 4 ohm dummy loads that can handle multiple hundreds of watts just laying around.

But... this will only be a BALLPARK figure, because without an oscilloscope to determine the clipping point of the amp, you really can't tell when you're at the maximum clean output.

But... even if you do this, as mentioned above, speakers aren't purely resistive. Not only does their resistance vary with frequency, but they also have a reactive element due to the inductance of the voice coil. This presents a more difficult load than a 4 ohm resistor, and most cheap amps will make considerably less power with a real speaker compared to a resistor.

 

Fluke DMMeter: $58.65 two years ago. Search the internet.
DCR, not resistance. DCR & Resistance (nominal) are two completely different beasts. Reactance, resistance are apples & oranges. Not too mention impedance rise from the enclosure. Do you know how to chart that? ... hmmm, I assumed (my error) that this was common knowledge.
Wrong.
again, wrong.

How do you set the sensitivity on your amplifer installs?? Do you just turn the lil gain **** until it "sounds about right"??

Parts Express for one example, Shanor Electric for another. 100 watt, <5%, 2-10ohm dummy loads can be had for $12-16.
This I can agree with. Especially depending on the manufacturer.
there is no such thing as Dumb Luck in math... sorry to tell you.

As I said, to do a proper bench test, you need alot more equipment. But again, the original poster was not looking for a bench test, it seems as if they wanted to know how much power they're driving their woofer with.
I do apologize for not addressing box impedance & gain setting earlier, I'd made the mistake of assuming it was common sense, common knowledge.

 

yea there is... ive seen people get the correct answer even tho what they did made no sense or was just plain wrong.


plus you are the first person to challenge NEEDAZ on this forum that ive seen and he has been right 100% of the time ive ever taken advice from him. This oughta be interesting.

 

Cheapest true RMS meter worth putting any money into is one of the Fluke 110 series meters, average MSRP of the available 110 series meters $140.00 with the 112 (good meter) coming in at $109.99 MSRP. Yes you can get better deals on line, but the average MSRP on the 110 series is $140.00.
If you’re not using a true RMS meter, any AC voltage reading not at 60Hz will not be right. Just give a calibration shop a call and ask them, they’ll tell you that typically with a non-true RMS meter the farther away you get for 60Hz, the displayed voltage will be lower and lower form what the real RMS value is. And this gets worse and worse the more complex thew waveform is. You said nothing about using a specific frequency or even a sign-wave, and straight music is pritte complex. Or just call and tell them you have a non-true RMS meter that you what calibrated at 60Hz, 120Hz, and 3kHz. Heck, even call METI, I know one of the Cal techs there, he could use a laugh. Those meters are only actuate at one frequency, usually 60Hz as that's what our houses are running along at.

No crap there not the same thing, that’s what is said. The speaker impedance will be highest at the speaker’s resonate frequency and then a high spot at the enclosures resonate frequency. I do know how it graph this and it’s not with a cheap non-true RMS meter.
But let me get this right, 85_ZED28 is asking if there is a way to measure the output power of his amp, and you think he’s going to JUST KNOW how to graph out a speaker impedance curve? And your assuming that this is common knowledge, most people get stuck and wiring subs and series or parallel, and your going to assume everyone will know how to PROPERLY plot out an impedance curve. If you’re using a non- true RMS meter then you didn’t know how to did it PROPERLY. What are you using as a frequency counter, or standard?

Not to mention that this isn’t what you said. You just told him to take a voltage measurement and gave him an equation, with an R and you never mentioned anything about frequency.

Do you remember typing this? Yes you followed up with "the right way", which wasn't right, just close. But to even post this as a "close to the right way" or "this will get you close to what you want" is wrong. You ARE putting out incorrect information.

There’s dumb luck if you’re not taken accurate measurements and just happen to get something right. If you’re measuring any frequency other 60Hz with a non-true RMS meter you are not taking actuate measurements. And doing it the way you said he would be taking the measurement with music, not a sign wave.

$12-$16 for a 100W audio load is a good price, but most people are running serial hundred watt to there subs. Again, no mention of frequency. And most places don’t have audio dummy loads that’ll dump a 1KW.

So again, non-true RMS meter, V^2/R=W , and you’re not going to get a number for W that mean anything. If not a sign wave at 60Hz, V is wrong, no explanation of R or how to get it, W isn’t going to right!

 

OH BURN... :hail: NEEDAZ:hail:

 

Thanx Bob, but I've been wrong before. I was wrong when I got out of bed this morning .
Ask Jim, he's got me on a couple things (but not the bed thing). It's not so much a mater of a BURN, but other people will read this, now and in a couple of weeks. I just think it's important to keep an actuate record of things so when people see them down the road read it there's no gray area.

 

Okay, I completely apologize for not going into exact detail. I apologize for assuming that people now what / why they are spending their respective money on audio equipment. I apologize for forgetting which forum I was posting on. And, finally I apologize for seeming as if I were "challenging You", this was not my intent. I simply react poorly when people try to call BS. Knee-jerk.

Would You mind calc'ing the most efficient means of avoiding power compression to a pair of 9915 Quad 0.7 dcr in a 6.4 cube Helmholtz wall with 680 sqin of port area with a second chamber/cabin area of 24.8 cu ft? I'm looking at an Orion 2500D per coil with a very solid 17.6-17.8vdc supply.

Thanks

Again, sorry for forgetting that not everyone does their homework, and thats what I get for ***-uming.

 

Originally posted by ME
Originally Posted by NEEDAZ
thats why i didnt say 100% of everytime but only when ive taken your advice...


now as for this thread.. i never thought id learn physics in an online squable over having to rate the power of an amp.. lol

 

I should apologize for pulling out the B.S. so fast. It’s not that I take personal offence to what you posted, it’s just there’s so much B.S. out there on this topic and others I think it’s important to keep as much of it as possible out of this form. Despite what you meant or intended, if someone read your first post down the road they would think they could just go out with a DMM set to AC volts, take a measurement, run the math, and have something, but they don’t. That’s why I came back so hard, and I apologize for the harsh tone of the post, not the content.

There are a lot of vary knowledgeable people on this form, and from your last post it sounds like your are a vary knowledgeable person as well. BUT, not every one here is, and that’s fine. For a lot of people this form is a big part of there “homework”. If the person is asking a question, they obviously don‘t know the answer. Do you and I know it’s better to get your info from more than one source? I hope. But to someone starting out in the hobby, they may not know where else to go for good info, or may not want to know any more then what it takes to get a CD player in their dash. And if that’s all the farther they want to go, or they just started and don’t know that’s fine. That’s why they're here and that’s why the information posted is so important. There are plenty of other forms out there that have all the bad info you could waste your time on, I was just trying to keep this form as detailed and accurate as possible.
Like I said, the second option your gave can get you close, but you have to under stand that it could easily be 20% off. If you under stand that and are willing to accept a 20% tolerance great. I don’t like anything over 10% as a rule of thumb. Just remember the loads need to be high power, non-inductive loads, and it’s harder for an amp to drive a speaker then a resistor. In my limited experience you’ll calculate a 10-20% higher power into a resistor then the amp can give a speaker. The higher quality amps will get closer, maybe 5-10%.

And for your question, I couldn’t even start. There are limitations to what I know, vary big limitations. So I won’t even try. But there are also things I do know. There are people here that could answer your question. And if you start it in a new thread, I WILL follow the posts so that hopefully I can fill in some of the gaps in my knowledge. I would love to see more truly "high-end" discussions in here.

Again, I apologize for pulling out the B.S. flag so fast. Next time I will try to go down the clarification rout first.

 

i must agree... i would love to learn all of the intricacies to calcing this stuff. i find it useful and interesting.

 

I honestly would like to see more in depth box discussions. I can get an electron to do exactly what I want. But getting air to do exactly what I want is a different store. Doing some reading but not enough time to invest in building and experimenting. Plaining on building a slot ported box over the winter, getting some different subs and see what happens.

 

how confident are you with the theory behind the basic ported?

there are oodles of links and actual paper books that make a great foundation for acoustics research.

 

just a poke...

if you want to know what your amp is rated for in watts according to the manufacturer, how bout the birth certificate of the amp? Provided the amp comes with one that is.

But seriously, this is a cool thread, I have been edumacated in alot of this stuff, but its been a few years.

Good job guys.

 

Unfortunatly, not alot of manufacturers supply these anymore. The other problem: there is still not standard of measurement for bc sheets. I cant recall which, but one of them used to birth/bench @ 14.4.