Amplifier Efficiency
04-05-2005, 08:30 PM
#21
Guest
Posts: n/a
Everything is True RMS - the only way to make anything else work is to test everything at 60Hz, and I use a 1kHz test tone.
The math is output power / (input current x voltage).
I have two scopes running on the bench at all times - One to monitor the test signal and one to monitor the output of the amplifiers. I also have a distortion meter so I know when they hit 1%, but at this point, after about 400 reviews, I can eyeball that part pretty good - it's only the amps that start to ring or distort (other than clipping) where this becomes important.
I've spent thousands on test equipment to do this stuff correctly. Pluse, that's what my clients expect.
The math is output power / (input current x voltage).
I have two scopes running on the bench at all times - One to monitor the test signal and one to monitor the output of the amplifiers. I also have a distortion meter so I know when they hit 1%, but at this point, after about 400 reviews, I can eyeball that part pretty good - it's only the amps that start to ring or distort (other than clipping) where this becomes important.
I've spent thousands on test equipment to do this stuff correctly. Pluse, that's what my clients expect.
04-06-2005, 12:27 AM
#22
Dave, 100w of RMS averaged sine wave is NOT equavalent to a 100w of DC power (coincidently RMS averaged square wave is)
Taking the root mean square average of a data set is only a type of average.... and it is not necassarily equal to the true average....
Do the math and you will see that your measurments are off by a factor of 1.1116 and your %69 averages are more like %62 in reality...
Thats about what I would expect out of an effecient AB class amp playing sine at full gain... [img]graemlins/thumb.gif[/img]
Taking the root mean square average of a data set is only a type of average.... and it is not necassarily equal to the true average....
Do the math and you will see that your measurments are off by a factor of 1.1116 and your %69 averages are more like %62 in reality...
Thats about what I would expect out of an effecient AB class amp playing sine at full gain... [img]graemlins/thumb.gif[/img]
04-06-2005, 04:56 AM
#24
actually... you don't average the sine wave to get the DC equivelant, you take the root mean square. Which is equivalent to dividing the peak power by half, or to taking the peak voltage and peak current and dividing each by the square root of 2, then multiplying them together. but only for a true sine wave, but since that's what dave uses, we'll go with that. The only interesting part comes when you are running through an inductor such as a voice coil. Then you get the voltage and current being out of phase, so your watts cannot be calculated by a simple volts * amps formula, you need to factor in the inductance.
but what do I know? I just spent 10 weeks studying this.
oh, and your average to RMS formula is backwards... the average is 90% of the RMS, so for the 69% to be off, you'd have to multiply it by 1.1111111111 giving you a LARGER number.
Average and RMS are not the same. RMS is the true measure of the power applied to the device (in a resistive load) perhaps you need a few classes in electrical theory?
On that note, Good job Dave!!
but what do I know? I just spent 10 weeks studying this.
oh, and your average to RMS formula is backwards... the average is 90% of the RMS, so for the 69% to be off, you'd have to multiply it by 1.1111111111 giving you a LARGER number.
Average and RMS are not the same. RMS is the true measure of the power applied to the device (in a resistive load) perhaps you need a few classes in electrical theory?
On that note, Good job Dave!!
04-06-2005, 10:28 AM
#25
inductance will effect impedance and thats about all we need to know for an averaged value.... and sorry but Iam correct... look it up if you want...
The true average of a sine waveform is .636 times its peak... any EE or even anyone who has taken a fairly intensive calculus class can tell you that...
Edit:
Look you just said it yourself... and it's 89.96% actually.....
[ April 06, 2005, 04:32 PM: Message edited by: Haunz ]
The true average of a sine waveform is .636 times its peak... any EE or even anyone who has taken a fairly intensive calculus class can tell you that...
Edit:
Originally posted by Sassmaster:
the average is 90% of the RMS
the average is 90% of the RMS
Originally posted by Sassmaster:
perhaps you need a few classes in electrical theory?
perhaps you need a few classes in electrical theory?
[ April 06, 2005, 04:32 PM: Message edited by: Haunz ]
04-06-2005, 01:58 PM
#26
anyone with a clue can tell you that the DC equivelant is the RMS value of the peak, not the average.
and inductance affects the phasing of the current as compared to the voltage, which causes power factor losses, speficic to the frequency applied to the inductor at any given moment. so the VA from the amp does not equal the watts output the speaker actually can use.
and inductance affects the phasing of the current as compared to the voltage, which causes power factor losses, speficic to the frequency applied to the inductor at any given moment. so the VA from the amp does not equal the watts output the speaker actually can use.
04-06-2005, 02:22 PM
#28
Originally posted by Sassmaster:
anyone with a clue can tell you that the DC equivelant is the RMS value of the peak, not the average.
anyone with a clue can tell you that the DC equivelant is the RMS value of the peak, not the average.
[ April 06, 2005, 04:31 PM: Message edited by: Haunz ]
04-11-2005, 11:15 PM
#30
Goalie Man
Join Date: May 2003
Posts: 1,412
ok enough gripping. heres what ya do. go by a amp thats big enough for your needs put it in your car and hook it up. if its not loud enough take it back to the store and by a..... ready...... bigger amp. voila who needs power specs your ears will be and always are the deciding factor!! lol. just thought i would lighten the air around here a little bit.. oh by the way did you here the one about our government going to bat for us canadians and demanding george bush and sudam hussain lower the price of gas to what it should be or we will shut off the water to california.
