Wpc

[JohnnieB]

Ok time for me to go to school. If this has been posted I have not seen it and google has been no help. How do you determine wpc all channels driven on an avr that only gives 2 channel spec? Im sure this has probably been explained a hundre times but thanks in advance for your help.

 

[j_garcia]

Where did you find one that doesn't list the typical output with all channels driven? Usually all of them list the 2ch rating because it is the highest, so you can expect all channels driven to be a fair step down, but it depends on what receiver we're talking about.

 

[markw]

All decent units will give both two channel and all channel specs. You may need to check more than one source to find out though.

 

[AcuDefTechGuy]

<OSome examples: 8 ohms 2Ch/5Ch = ratio

$5000 Arcam 600: 119/96 = 1.2
$5500 AudioControl 1: 120/106 = 1.1
$2000 Anthem 700: 160/94 = 1.7
$1600 NAD 757: 122/91 = 1.3
<O$1200 Denon 3312: 143/103 = 1.4<O</O
$1200 Yamaha RX-A1020: 129/73 = 1.8
$1000 Anthem 300: 116/83 = 1.4
<O</O$1300 Cambridge 551: 111/81 = 1.4
$230 Sony 520: 142/81 = 1.8
$330 Pioneer 821: 110/78 = 1.4
$350 Denon 1612: 119/80 = 1.5
$450 Pioneer VSX42: 118/80 = 1.5

So I would say the 2Ch/5Ch ratio is usually anywhere from 1.1 to 1.8.

So if an AVR is 120WPC x 2Ch into 8 ohms, then the 5Ch might be anywhere from 67WPC to 109WPC.
</O

 

[PENG]

Too bad there is no way to calculate it from the published power consumption figures for at least two main reasons, 1) There don't seem to be a standard that manufacturers all adhere to. 2) Some provide power consumption, and then maximum power consumption while others provides just one and either way you can only guess what they really are based on. Also, even if they all use the same standard, they don't tell you their efficiencies, nor do they tell you how much of that power consumed are for the power amp. For example, Onkyo's top models tend to have larger power supplies and consumptions figures, but they probably operate at lower efficiencies, judging from the heats they produced, as well as the HQV vides chips that probably also consume more power.

The best way to get an idea is to search for credible lab measurement figures. S&V can be a good place to look as they do have quite a few in their archive. Their See ADTG's post for more info.

 

[Swerd]

The US Federal Trade Commission (FTC) requires stereo and AV receiver makers to state the power output measured by the RMS method, at 20-20k Hz, when two channels are driving 8 ohm loads, while stating the THD at the rated power. They do not require similar ratings for more than two channels.

So you can always compare two receivers by their FTC power ratings. It would be easy to guess that the power would be less if 5 or 7 channels are driven, but you won't know what that value is unless you measure it.

Many (but not all) receiver makers now provide an all-channels-driven rating, but older receivers may not have that information available. And, as others have already said, there is no standard way to measure that, so even if two receivers provide such numbers, it still may not be an apples-to-apples comparison.

 

[JohnnieB]

Thanks e'one for the replys. The receiver is an Onkyo TX SR-875. If I remember my electrical formulas correctly, volts x amps = watts? Not sure how this applies if I don't know the actual amp draw of the receiver.

 

[markw]

Here's a copy of that units owners manual. You're right. It doesn't come out and state what it's all channels driven ratings are. I've never come across that before. That makes me mistrust Onkyo even more than I did before.

 

[PENG]

Thanks e'one for the replys. The receiver is an Onkyo TX SR-875. If I remember my electrical formulas correctly, volts x amps = watts? Not sure how this applies if I don't know the actual amp draw of the receiver.

Not really, that formula is only correct if the load is purely resistive and assumging you are referring to power output developed across the load. At any instant, the output power across the load would be more like volt across the load (speaker terminals) X the current through the load X the cosine of the angle between the voltage and current phasors (or vectors). The power calculated this way would be known as the average power (or RMS as commonly quoted but that is not technically correct) if the voltage and current readins are in RMS, or peak if the readings taken are just instantaneous peak values.

 

[Swerd]

From p 117 of the Onkyo manual:

North American TX-SR875:
140 watts minimum continuous power per channel, 8 ohm loads, 2 channels driven from 20 Hz to 20 kHz, with a maximum total harmonic distortion of 0.05% (FTC)

160 watts minimum continuous power per channel, 8 ohm loads, 2 channels driven at 1 kHz, with a maximum total harmonic distortion of 0.7% (FTC)

170 watts minimum continuous power per channel, 6 ohm loads, 2 channels driven at 1 kHz, with a maximum total harmonic distortion of 0.1% (FTC)

Here's a copy of that units owners manual. You're right. It doesn't come out and state what it's all channels driven ratings are. I've never come across that before. That makes me mistrust Onkyo even more than I did before.

It depends on when this model was made. I'm not sure exactly when the all channels driven thing started among most of the big Japanese makers, but maybe it was 2 or 3 years ago. Onkyo is clearly following the FTC requirements.

Thanks e'one for the replys. The receiver is an Onkyo TX SR-875. If I remember my electrical formulas correctly, volts x amps = watts? Not sure how this applies if I don't know the actual amp draw of the receiver.

With a loudspeaker, the impedance varies with the frequency of the musical signal. It's not constant. Peng has spelled out the other variables and details correctly.

 

[JohnnieB]

Ok, cosign at angle of vectors just popped a fuse. You have reached the limit of my mathematical prowess. Admittedly, that didn't take long.

 

[PENG]

Ok, cosign at angle of vectors just popped a fuse. You have reached the limit of my mathematical prowess. Admittedly, that didn't take long.

I did not say cosign, I said cosine, the short form is 'Cos'. It is a trigonometry function:

Trigonometric functions - Wikipedia, the free encyclopedia

As for the term vector, in electrical engineering we typically refer to phasor diagrams that show the phase relationship between voltage and current in an ac circuit where the load is reactive, such as an inductor, capacitor, or a combination of resistance, inductance and capacitance in series, parallel or combinations of all. In such phasor diagrams, the voltage and current are referred to as phasors rather than vectors.

Since you said "Ok time for me to go to school." Below are more readings on the power formula:

Phasor Diagram and Phasor Algebra used in AC Circuits

Review of single phase power circuits

Electric power - Wikipedia, the free encyclopedia

 

[JohnnieB]

Thanks Peng, you have no idea how difficult that looks to me. I couldn't get through basic algebra, some sort of mental block keeps me from understanding it. I think it's what may be referred to as stupidity. Oh well, such is life. They say ignorance is bliss. Ill study this, see what happens, maybe an epiphany.