[chinzo]

Can someone please explain to me what does it mean by "2 channels driven" on AV receivers. For instance, on Pioneer VSX-524 (5 channel) receiver, it says 80 watts per channel with 2 channels driven.

I know it is a very basic question, I did google it, but still don't get it. Please explain like you would to a 5 years old.

 

[robbo266317]

This is the power that is available when used in stereo mode. (two channels only)
When you use it for surround sound the available power per channel may be less than this if the power supply cannot provide enough current.

 

[chashint]

When a reputable manufacturer states 80 watts / two channels driven what that typically means is the unit will produce 80 watts output power on two channels simultaneously when both of the channels are driven with a 1kHz sine wave. Total harmonic distortion (THD) will also be stated for that output power.
You can reasonably expect the THD will be about 0.1% at full rated 2 channel driven power.
If the THD is greater than 1.0% or not stated at all that is a huge red flag.
Something else to be aware of is if more than two channels are driven on the AVR with the 1kHz sine wave the unit will not be able to output the 2 channel rated power (in your case 80 watts) into 3/4/5 channels simultaneously.
Even though I told you about it in my opinion you do not need to worry about the all channels driven condition because that will never happen in the real world, it is a laboratory test condition. (For full disclosure the majority of the people on the forum do not agree with me about the importance of the all channel driven teat, but that's ok...forums exist so people with differing opinions can argue their case.)

When we are talking about reputable AVRs Denon, Pioneer, Onkyo, Marantz, and most Sony make the list.

Please ask more questions, even the most knowledgable person here started at step one at some point.

 

[GCG]

When you read these claims it's important to realize that the marketing departments of each company is going to want to "turn its best side to the camera" so to speak. Your manual states 80w + 80w into 8Ω with no more than 0.08% THD in Stereo. Right below that it makes the very valid claim to produce 140w for each channel into 6Ω with no more than 1% THD. This shows two things: (1) How high the power can go before the THD begins to get too noticeable and (2) That, yes, ohms law is still in force and if you lower the impedance of the speakers (the load), voltage goes down, and current goes up. Since one of the limits on a power supply is the maximum voltage +/- that it can deliver (the voltage "rails") with lower impedance speakers the amp is able to develop more power in that speaker before it clips. Net result is that at the minimum impedance (6Ω), for the highest "acceptable" THD (1%:innocent you could push the amp to 140 watts on a single channel.

Later it specifies that the total power consumed by the power supply is 415w which is the absolute maximum that it could deliver to the speakers (less really because some is needed to drive the internal electronics). 5 x 140 = 700 watts so there is no way that this power supply will drive all 5 channels to a full 140 watts into 6Ω and will be limited to something less than 80w into 8Ω. Not to worry most listening is done at or less than 1-3 watts anyway. You only need the higher power for the occasional transient burst.

Don't worry. You're not being cheated. These are the kinds of games that must be played to counter the very deceptive claims of less reputable manufacturers. Otherwise the good ones would see a noticeable drop in sales.

 

[tonyvdb]

The test that is done to see how well a receiver does is in its self flawed. A 1kHz test tone is not even a realistic load. Music and even more so movies have a very wide dynamic range of frequencies and the deeper the dynamics the harder the load on the amps.
There is much debate about this topic but the general consensus is that as you add more channels to the power supply the less output you will have on reserve. Movie soundtracks particularly action movies will run all 5 or 7 channels simultaneously and this will in turn drop the receivers ability to maintain its rated output by as much as half.
More info on that topic can be found here

 

[GCG]

The test that is done to see how well a receiver does is in its self flawed. A 1kHz test tone is not even a realistic load. Music and even more so movies have a very wide dynamic range of frequencies and the deeper the dynamics the harder the load on the amps.
There is much debate about this topic but the general consensus is that as you add more channels to the power supply the less output you will have on reserve. Movie soundtracks particularly action movies will run all 5 or 7 channels simultaneously and this will in turn drop the receivers ability to maintain its rated output by as much as half.
More info on that topic can be found here

I agree, but in the defense of the better manufacturers, it's fair to state that in a debate if a dishonest person is willing to lie to an under educated and under informed audience then the honest person is at a disadvantage and must take more care in how to state the case to support honest claims in their favor.

 

[AudiocRaver]

A fine point, not trying to muddy the waters, there are SO many ways to specify these things:

The total power being pulled from a power supply can exceed the total power in (consumed) for a very short time, i.e. a few cycles of peak audio. Obviously, as the input power is less than the output power (not even taking efficiency into account), the power supply voltages will start to drop, so it cannot be done for long. Don't even know if manufacturers push the limits this far, but it is theoretically possible. The more reputable manufacturers that HTS members tend to favor would probably not push their spec limits to this degree, though.

 

[GCG]

I guess, really, we've answered the OP's question and I don't really want to hijack the topic. Suffice to say that this, like so much else, is a matter of caveat emptor (let the buyer beware). Find a good brand that gets good reviews that are backed up with solid lab tests (I like Sound and Vision). Avoid the dodgy ones that couldn't pass a decent review on a bet. Learn to read the specs (like the OP is doing here:clap::T) and you're on a path to success.

 

[chinzo]

I think this question should have been posted on Yahoo answers/questions.

You are right about that. I am just beginning to learn to read the specs, both on home and car audio. I will revisit this thread after I learn all the basics, starting from the term THD.

Thanks for all answers.

 

[Glen B]

(For full disclosure the majority of the people on the forum do not agree with me about the importance of the all channel driven teat, but that's ok...forums exist so people with differing opinions can argue their case.)

Count me on your side of the debate. I see no problem with AVRs not being able to deliver full power to all channels simultaneously, when such performance will never be required in real world use. Based on my measurements, the front channels and subs require the most power, and the latter most ofter are self-powered. The money saved by manufacturers from smaller power supplies can go into what people want the most, the very latest bells and whistles at affordable prices. People can't have their cake and eat it too.

 

[AudiocRaver]

Good point on subs always being self-powered, or calling for separate monster power amps. If we took a poll of how many HTS-types have subs powered directly from their AVRs, I wonder if there would be a single yes vote. Anyone? Not that there's anything wrong with it.:R

Another thought: There is a big difference between never and rarely. Has there never been a movie where all 5 channels hit peak at the same time for a tenth of a second? In the realm of today's effects-laden movies & mixes, that would surprise me. Bear in mind I am not a cinema soundtrack expert or anything close to if, just thinking of the effectsy movies I have been batterered with down at Sonnie's place (not complaining).

If I had one movie that I liked where this occurred, and I heard clipping when it was loud, I would not be happy. Then it becomes a matter of how much a fella is willing to pay to insure against that rare event.

Music is quite another matter. Virtually ALL music today other than classical and jazz is mixed to run at or so close to clipping during loud passages that one can assume full scale output swings on a regular, if not constant, basis. Talking stereo, of course, so this applies mainly to 2-channel amp specs. Headroom should be planned accordingly. In a way it is easier with modern music, the dynamic range is small enough (8 dB to 12 dB) that large headroom budgets are totally unnecessary.

But that, as chashint wisely pointed out, is just my opinion.lddude:

 

[GCG]

Hear's a what-if this discussion brings to mind. Many of us have the capacity to offload at least the two front channels to a separate amp(s). The down side of that is finding an amp with the specs to match what the AVR has (or better) and this could present a cost impediment. Why not allow for the addition of a separate power supply to abrogate the drawbacks of what are often limitations in the ones supplied? If the reference (the common) were solid enough the cost could be considerably less than a comparable power supply AND amplifier combination. What brought this to mind is a "D" class amp I'm giving as a Christmas gift that has a separate PS but which is under powered for the rated output. I've already researched a higher current replacement PS as a suggestion in the event the supplied configuration is inadequate.

 

[AudiocRaver]

It makes sense from the user perspective. From the manufacturer perspective, it is like saying, "we didn't design it right, so here is a way for you to fix it." Their closest approach to what you suggest is probably their separate preamp / power amp offerings.:dontknow:

 

[tonyvdb]

Hear's a what-if this discussion brings to mind. Many of us have the capacity to offload at least the two front channels to a separate amp(s).

Yes, and this again is a problem because many people who buy the lower end receivers have no pre-outs (Low end receivers suffer the greatest with this issue) so that is not possible. I would think that some of us who choose to spend more money to get the pre-outs know that being underpowered is a problem but how many new buyers know this and more so how many understand that distortion is a big reason why many speakers dont sound as good as they should.
Ive heard so many people say that they dont like the sound they get from said receiver and then get told to buy different speakers or simply thats just the way it is.

 

[chashint]

I think this question should have been posted on Yahoo answers/questions.
You are right about that. I am just beginning to learn to read the specs, both on home and car audio. I will revisit this thread after I learn all the basics, starting from the term THD.
Thanks for all answers.

I think you asked the question in the appropriate place.
If we did not answer in a manner that makes sense please ask more questions.
Sometimes (most of the time) when the group 'thinks' the question has been answered we ponder among ourselves and threads meander a bit.
I assure you the group wants to help and will try to explain anything you want to talk about.

 

[AudiocRaver]

Sorry/not sorry, I know sometimes it is nice to get a simple answer, but sometimes there is not a simple answer to some questions.

We really are trying to be helpful.

 

[GCG]

@ Chinzo I tutored this stuff in college. You don't need to go elsewhere for help when you have resources here. Would a more detailed primer in the basics presented here be helpful? I could work something up for you.

 

[AudiocRaver]

@ Chinzo I tutored this stuff in college. You don't need to go elsewhere for help when you have resources here. Would a more detailed primer in the basics presented here be helpful? I could work something up for you.

Thank you, GCG. It might be helpful for many of us.:T

 

[GCG]

OkyDoky Gimme a little while to write something up.

 

[GCG]

I'm going to start off VERY basic to make sure no one is left behind so be patient.

Reproducing recorded music is the last process in a chain of events that starts with the artist/musician and ends with our brains interpreting the compressions of air produced by speakers as sound. How faithfully the sound we hear matches what was originally played/sung is how most determine the quality of the reproduction. We all want the experience in our living rooms to be as close as possible to what was produced in the recording studio or concert stage. Understanding how that happens in the systems we own will go a long way to finding the best components for our given tastes, capacities, and budgets.

The sound we hear at home is produced when the driver cone(s) in a speaker move(s) back and forth, compressing air. If the motion occurs 261.626 times a second we hear middle C. We need to know just how that cone is placed into motion. What effect does the quality of the components have on the accuracy of the motion and therefor the quality of the reproduction. I’m sad to report that this involves an understanding of some basic to intermediate concepts in electricity.

The thing that moves the cone of a speaker driver is the voice coil, a coil of wire inside the driver that rests in the magnetic field of a doughnut shaped magnet. When electric current passes through the voice coil it moves and, being attached to the cone, the cone moves as well. Reverse the direction of the current flow and the coil and cone reverse direction as well. Do that 262.626 times a second and – viola – middle C.

… but what is this current stuff? …

Current is the flow of electrons in a conductor. The wire in the voice coil is a conductor – copper. Other conductors are gold, silver, iron, aluminum, and mostly any metal. Ceramics (among other things) can be conductors, too, but that’s another subject. If a specific number of electrons called a coulomb (very big number you that don’t really need to know) pass a particular point on a conductor in 1 second we call that 1 ampere of current.

I = Q/t … Where I is current in amps (ampere), Q is charge (electrons) in coulombs, and t is time in seconds.

Now that we know what current is, what makes it happen? It’s good to think of current flow a wire similar to water flowing in pipes. To get water to flow we need pressure like from filling up a barrel. Water will flow from the bottom of the barrel if a pipe is attached and continue at a diminishing rate as the barrel empties. The height of the water in the barrel produces the pressure by virtue of the weight of the water above the pipe. The counterpart in electricity is EMF – Electromotive force – It’s measured in Volts and is commonly referred to as voltage. It is the “pressure” in an electrical circuit.

Back in the barrel example, the amount of water that will flow will be determined by how big the pipe is in diameter. The smaller the pipe’s diameter the less water will flow for a given pressure (water height). A smaller pipe exerts more Resistance to the flow than a big pipe does. There is a counterpart in electricity that is called (are you ready?) Resistance. Resistance is measured in Ohms, that’s right, the same thing that speakers are rated in. You may have made the connection by now that somehow the amp creates EMF (voltage) that causes current in the speaker voice coil wire and is somehow affected by the speaker’s resistance. If you did you’re on the right track but we left off one more important item – Power – and that’s measured in watts. Put all four of these - V(voltage),I(current),R(resistance), and P(Power) - together and we have the four cornerstones of electricity called Ohm’s Law and that’s where we go next.