Understanding WPC (watts per channel)

[busterbrown]

I am 48 years and finally figured out why my receivers over the years
have gone into protect mode or shut down. When you look at the specs on
a receiver you look at wpc, let's say 110, that's 110 by 2 ch driven or 2 speakers, that's 220 watts that the receiver can drive period !. If your
watching 5.1 surround thats 5 channels driven the receiver is pushing
42 wpc, depending on volume and the loudness of a particular scene is when
the receiver would go into protect mode. let's say you have volume at 10,
the front speaker might be pulling 35 watts, but there is a explosion or
airplane crashing or whatever and that scene causes the speaker to pull
50 watts then the speaker distorts the receiver clip and you need new speakers
I believe the industry is not as misleading as they are not forthright.
Before there was surround sound there was stereo (2 ch) and they would
say 110 wpc, today it is the same and it's true, but the amp makers
should have to add 5,7,9 wpc:

110 wpc x 2----42 wpc x 5----30 wpc x 7---23 wpc x 9

[Steve]

Huh?

Why are you placing a 110 watt limit on the amp? It kinda sorta sounds like you're confusing the wattage that the receiver's amp puts out with the 110 volts that you get from the wall outlet. Lots and lots of receivers and amps out there put out waaaayyyyy more than 110 watts total. Or maybe I don't understand what you're saying.

[busterbrown]

It was just an example. I should have just used 100 watts kiss(keep it simple
stupid), but 110 popped in my head first, or I should have used my current
sony str dh820 which is 105 wpc 2 driven. (until i upgrade this summer).
Any wpc on the specs is 2 channels driven then divide that total # of watts
(210 in my case) then divide by # of channels to tell you how many watts the
receiver is pushing into said channels.

[busterbrown]

oh by the way I did say 220 watts total. i hope Big Daddy chimes in.

[Remo]

Here the bench test for the Onkyo TX-NR1009 for example.

2 channels driven continuously into 8-ohm loads:
0.1% distortion @ 145.7 watts
1% distortion @ 179.5 watts

5 channels driven continuously into 8-ohm loads:
0.1% distortion at 116.5 watts
1% distortion at 131.2 watts

7 channels driven continuously into 8-ohm loads:
0.1% distortion at 86.1 watts
1% distortion at 100.6 watts

Onkyo's spec states that is will output 135 watts per channels 2 channels driven @ .08% distortion.
So they are right on with their specs, they don't state any thing more than 2 channels driven though.

However the sticker they put on the front of it for all to see , says 9.2 channels 180 w/ch which is complete bunk and misleading for sure.

[pentatonic]

That's not really how it works, but you're on the right track. A receiver that puts out 110 WPC 2 channels driven will not put out 110 WPC all channels driven (though some very few do) but you can't take 220 W total and divide by 5 or 7. Some are better than others (certain Onkyos) but you should expect anywhere from 55-90 for each channels (these numbers are not accurate just very general) Where you are right is that the total wattage is directly related to the unit's power supply and its capacity to generate the power, the beefier the better (though with digital amplification this is different).

[Steve]

Originally Posted by busterbrown

It was just an example. I should have just used 100 watts kiss(keep it simple
stupid), but 110 popped in my head first, or I should have used my current
sony str dh820 which is 105 wpc 2 driven. (until i upgrade this summer).
Any wpc on the specs is 2 channels driven then divide that total # of watts
(210 in my case) then divide by # of channels to tell you how many watts the
receiver is pushing into said channels.

Originally Posted by busterbrown

oh by the way I did say 220 watts total. i hope Big Daddy chimes in.

Ok I got you now. Sorry for the misunderstanding. I see where you're coming from. And yes I agree that some manufacturers do print their specs in a way that's easily misconstrued, but not all. For instance here's the info page on the receiver I have, a Pioneer Elite SC-25.

http://www.pioneerelectronics.com/PU...eceivers/SC-25

Amplifier Design ICEpower® Direct Energy HD

Surround Power 140W x 7 (20Hz - 20kHz, .09% THD @ 8 ohms, All Channels Driven)

Stereo Power 140W x 2 (20Hz - 20kHz, .09% THD @ 8 ohms)

It gives a spec for two channels driven as well as for seven channels driven. Some do and some don't do this, and as noted above, with very few exceptions, receivers generally don't come anywhere close to their claimed wattage when bench tested.

[busterbrown]

Thank you both for further insight, I knew i would get some more detailed follow
up, just to bring more awareness to audio world, and simplify it a little.

[Jim Hawkins]

So just to through a little fun into the mix I will bring up my interesting story. I had a Onkyo 606 and an older Denon 345R stereo receiver. Using the same speakers the Denon was louder at 1/4 volume then the Onkyo at Half way. Now I based this on the dial of the Denon and the Total number volume of the Onkyo cut in half ( I think it was about 30). The Denon is rated at 45 wpc and the Onkyo is rated at 90 wpc at two channels. I only used music to compare in the two with the Onkyo in direct mode.

Is this an analog dial versus digital volume? Or is the input gain much higher on the Denon to account for this very noticeable volume difference?

[callas01]

Originally Posted by Jim Hawkins

So just to through a little fun into the mix I will bring up my interesting story. I had a Onkyo 606 and an older Denon 345R stereo receiver. Using the same speakers the Denon was louder at 1/4 volume then the Onkyo at Half way. Now I based this on the dial of the Denon and the Total number volume of the Onkyo cut in half ( I think it was about 30). The Denon is rated at 45 wpc and the Onkyo is rated at 90 wpc at two channels. I only used music to compare in the two with the Onkyo in direct mode.

Is this an analog dial versus digital volume? Or is the input gain much higher on the Denon to account for this very noticeable volume difference?

my naim integrated amp is much the same as your denon as compared to my integra. my naim will get louder quicker, and provide much better dynamics, as well as sonics and stereo imaging. my naim is also capable of power 2 ohm loads and 4 ohm loads for long periods, something my integra cannot do.

[Big Daddy]

If I were your physics teacher, I would force you to repeat the course again and run 100 laps.

You cannot simply add power (watts). If you do, I will strike you. You can only add voltage and current. Voltage represents the potentioal of the source. Current flows from the source and work (watts) takes place.

If you have a receiver that is rated 100 watts per channel, you do not get 200 watts if you combine the two channels . You get 400 watts. That is why when you bridge two channels of an amplifier, you get four times the rated power. To understand this, check the following example.

Example. Assume you have a receiver that is rated 100 watts per channel and the impedance of your speakers is 8 ohms.

Power (P) = 100 Watts per channel

Impedance of each speaker (R) = 8 Ohms

Ohms Law:

Power = Voltage Squared / Impedance

P = V^2 / R

V^2 = P * R

V = (P * R)^1/2

Plug the numbers into the equation and calculate the rated voltage per channel.

Voltage per channel (V) = (100 * 8)^1/2 = 28.3 Volts

Voltage for two channels (V + V) = 28.3 + 28.3 = 56.6 Volts

Go back to Ohm's law and calculate the combined power.

Combined Power for Two Channels (Watts) = (56.6)^2 / 8 = 400 Watts

[busterbrown]

thanks big daddy i am now confused. I drive 60 mph to go 60 miles how long will drive take ? LOL. seriously if specs say 100 watts 2 channel driven how many watts is it pushing into 5 and 7 then ?

[pentatonic]

Originally Posted by busterbrown

thanks big daddy i am now confused. I drive 60 mph to go 60 miles how long will drive take ? LOL. seriously if specs say 100 watts 2 channel driven how many watts is it pushing into 5 and 7 then ?

Depends on the receiver, you can't really generalize this. As mentioned a few posts up, some Pioneer models do deliver the rated power to all channels, all channels driven. Others also fair well, and then the rest but it really depends on the model. Digital amplification is usually closer to spec as it's a different type of amplifier and they also run very cool. They can be lighter also and it isn't a sign of a poor receiver. Traditional receivers rely (usually) on 1 power supply for all channels and the PS is the reason they can't achieve those numbers all ch driven as the PS just can't feed all the power necessary.

[WiWavelength]

Originally Posted by pentatonic

Digital amplification is usually closer to spec as it's a different type of amplifier and they also run very cool.

To clarify, class D amplification is not necessarily digital, and it usually is not. In the Pioneer class D AVRs, for example, the amplifier stage is driven by an analog signal.

AJ

[pentatonic]

Originally Posted by WiWavelength

To clarify, class D amplification is not necessarily digital, and it usually is not. In the Pioneer class D AVRs, for example, the amplifier stage is driven by an analog signal.

AJ

I was talking about digital amplification and though ICEpower was digital, my mistake

[Canada]

I wish all companies rated receivers with all channels driven, instead of just 2 channels driven (stereo). All channels driven would be a lot more transparent on the parts of the companies.

[Big Daddy]

Originally Posted by busterbrown

thanks big daddy i am now confused. I drive 60 mph to go 60 miles how long will drive take ? LOL. seriously if specs say 100 watts 2 channel driven how many watts is it pushing into 5 and 7 then ?

I made that post just to confuse you.

Kidding aside, my point was that you cannot simply add or subtract power (watts). Also, remember that when you bridge a stereo amplifier, you are essentially converting it to a mono amplifier in order to power a single speaker or a passive subwoofer. Think of bridging as connecting two mono channels in series. The impedance implication will be the opposite of series speakers. In the case of series speakers, the impedance will rise. When you bridge two channels of an amplifier, you will be cutting the effective load impedance in half. For example, if a bridged amplifier is connected to a 4 ohm speaker, it will make the effective impedance 2 ohms. This is why an amplifier can quadruple the rated power of a single channel when bridged. Many people believe that if their amplifier is stable for 4 ohm loads, then they can bridge it to a 4 ohm speaker load. This is not the case as a bridged amplifier will see the 4 ohm speaker as a 2 ohm speaker load and the amplifier may fail.

A bridged stereo amplifier will not have two channels of output available anymore. However, when people mention the power rating of an amplifier with 2 or 5 channels running, all channels of the amplifier are available at all times. Depending on the audio content, the sound may come out of one speaker, two speakers, or multiple speakers.

It is also important to mention that Class D amplifier does not mean digital. The letter D does not stand for digital.

Going back to your original question, it is not possible to guess an amplifier’s behavior when all channels are running, given the fact that you know its power rating when two channels are running simultaneously.

Sound & Vision Magazine does a pretty good job of reviewing AV receivers. They usually publish the power ratings as you increase the number of channels. Here are some examples:


Sony STR-DA5800ES A/V Receiver



Yamaha RX-A3020 A/V Receiver



Cambridge Audio Azur 551R A/V Receiver


Pioneer VSX-60 A/V Receiver



NAD T757 A/V Receiver



Pioneer Elite VSX-52 A/V Receiver
PioneerEliteVSX-52.jpg


Onkyo TX-NR509 A/V Receiver

[busterbrown]

Thanks Big Daddy, I guess i cannot say "no I stayed at a holiday Inn last
night". No one can figure out from the specs only from bench testing I guess.
I am going to upgrade from $300 sony strDH 820 (105 wpc) to yamaha RX a2020 and
add Emotiva XPA-3 or 5 to power Polk RTI a9's CSIA6 center and 7.2 or 9.2
I was watching beach landing in "saving Private Ryan" (7.1) a little louder
than usual (it was sounding sooo good) the receiver went into protect
and damaged 1 midrange and a tweeter in same tower (since repaired).
Is this the way to go ?