Underrated, overrated... How do you know?

[squeak9798 5,000+ posts]

Take a DMM (digital multimeter)set it to AC voltage, with the appropriate sensitivity

hold test leads to the +, - of the channel being tested

blast tone or music at maximum unclipped level

record highest voltage displayed

multiply voltage by itself then divide by resistance of speaker connected to channel.

for example-

34 volts peak is recorded, channel is connected to a 2 ohm speaker/load

peak volts squared

34X34=1156

divided by resistance

1156 / 2= 578 watts

Peak output recorded as 578 watts, to obtain RMS voltage multiply by .727

578x.727= 420 watts rms

This is NOT the most accurate way to find the true RMS rating of your amplifier, there are a lot variables that are not accounted for when you test like this, therefore this test is only to be used to give a better understanding of what your amplifier is capable of doing.

It's .707, not .727 //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Now, the truly important part of the above post is the bolded section. This test WILL NOT give you the true, accurate RMS pow output of your amp. So don't do this and start run around talking about how underrated and/or overrated your amp is because of the simple fact that the test you conducted was in no way accurate.

For those interested, here is the TRUE way to measure your amplifiers RMS power output: http://www.bcae1.com/measpwr.htm

 

[ballstothewall 10+ year member]

Ok, I know the P=V^2/R....But how do you get 0.7071067812, I am curious.

Thanks

-Ryan

 

[audiolife 5,000+ posts]

i just use the force

 

[supa_c 5,000+ posts]

That works too...but not everyone is a jedi

 

[jsloan10 10+ year member]

"It's .707, not .727"

OPPS mybad! //content.invisioncic.com/y282845/emoticons/blush.gif.99bc659ee2012b7d826165e26fb5eebe.gif , Thank you for correcting that, I must have been daydreaming while I was typing.

 

[Tirefryr 10+ year member]

That would probably work running a 60hz sine wave.

Can you tell me why?

 

[jsloan10 10+ year member]

I would assume its because household current is 110 to 120 volt AC at 60hz, thats why you can hook up a sub to a wall outlet and get "sound", I wouldnt reccomend it though, as most subs will go up in smoke within seconds.

The "ghetto" test I suggested can give you a point of reference between 2 amplifiers given that you test the 2 amps with the same load and frequency, squeak9798's link is the only true way to measure a real rms rating.

In the end the best test equipment overall is your own ears, all the numbers and brand names in the world mean nothing if it doesnt sound good to you.

 

[Tirefryr 10+ year member]

I would assume its because household current is 110 to 120 volt AC at 60hz

I see the theory behind this, but not the principle. Europe and many Asian countries run on 50 cycles. So if my amp is produced overseas and was tested at 50 cycles that would mean the power ratings are different than at 60 cycles. See what I'm getting at? If there's something else to it, someone please let me know.

 

[jsloan10 10+ year member]

Your putting too much thought into it, forget about the houshold current thing, all amps recieve roughly 12 to 14 volts to produce power and all amps nomatter where they come from are tested using voltages found in vehicle charging systems, most stardard testing voltages are 12volts, 13.8 volts and 14.4volts, CEA uses 14,4 volts for its testing measures.

So you take an amp, power it with 14.4 volts DC and connect the output to a resistive load then play a sinewave through the amp (like 60hz or 50hz) and measure the amount of AC voltage coming from the outputs on the amp and do the formula, doesn't matter where you live, the procedure is the same.

Be sure to check the link that squeak9798 put up for the full explaination.

 

[Tirefryr 10+ year member]

Typically the amp is going to output more power at higher frequency though. One of the reasons for the CEA compliance. If an amp that normally would do 100 watts at 40Hz now does 1000watts at 4KHz, does that mean you rate the amp at 1KW? Little exagerrated, but you get my point.

This is why I was asking the relevance of the 60 cycle tone, or for that matter, how do you really choose? Too many ways to skew the results.

 

[jsloan10 10+ year member]

Thats why they test using a resistor instead of a speaker, as the speakers resistance will change at different frequencys while the resistor will stay the same at any frequency.

this is the main reason why my test is inaccurate, but could be used to compare different amps into the same speaker at the same frequency with the same input power.

 

[squeak9798 5,000+ posts]

I see the theory behind this, but not the principle. Europe and many Asian countries run on 50 cycles. So if my amp is produced overseas and was tested at 50 cycles that would mean the power ratings are different than at 60 cycles. See what I'm getting at? If there's something else to it, someone please let me know.

I believe he said that because DMM's are going to typically be more accurate in that frequency region due to their being based off of our household electrical frequency of 60hz. That's the frequency area that they were designed to measure.

DMM's do start loosing their accuracy once you are out of the certain frequency bandwidth.

 

[Tirefryr 10+ year member]

I believe he said that because DMM's are going to typically be more accurate in that frequency region due to their being based off of our household electrical frequency of 60hz. That's the frequency area that they were designed to measure.
DMM's do start loosing their accuracy once you are out of the certain frequency bandwidth.

Now that seems more logical to me, although I could delve into the properties of different meters. But I won't.

 

[DFW40 10+ year member]

I have had many an amp but have never had a birthsheet with one. Is this normal?

 

[squeak9798 5,000+ posts]

I'd say that less than 50% of amps come with birthsheets.