# What is 2 channels driven?



## 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.


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## 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.


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## 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.


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## 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.


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## 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


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## GCG

tonyvdb said:


> 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.


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## 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.


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## 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.


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## 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.


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## Glen B

chashint said:


> (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.


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## 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:


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## 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.


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## 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:


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## tonyvdb

GCG said:


> 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.


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## chashint

chinzo said:


> 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.


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## 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.


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## 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.


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## AudiocRaver

GCG said:


> @ 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


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## GCG

OkyDoky Gimme a little while to write something up.


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## 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.


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## chinzo

Wow. Exactly what I needed. Soooo helpful. Thank you GCG and the rest. If there is more, please continue.hehe


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## GCG

I know we need to get to the OP’s question but I feel that insuring that everyone is at a similar level of understanding is important. Bear with me. I’ll be getting to power measurements, %THD thresholds, and the like soon (as long as the demands of the season don’t get in the way).

Ohm’s Law
Here’s a page that has the mathematical relationships between all the various components we discovered above. There is nearly no end of treatments on ohm’s law on the internet and it would be ridiculously redundant to add another. Please ask Uncle Google for a full explanation.

http://diyaudioprojects.com/Technical/Ohms-Law/

What isn't clear from the equations and many of the net treatments is the concept of the source and the load. The source in our case is the amplifier. The load is the speaker or more specifically the current drawn by it. Notice I said DRAWN. Make no mistake the passive downstream component, the speaker, can best be described as DRAWING current from the amp and the only thing you need to prove it is the breaker panel in your home. If the source had the capacity to limit the flow of current in a circuit we wouldn't need breakers, fuses or any other protection. If the resistance in a circuit goes lower, as long as the voltage remains constant the current will rise. *WITHOUT LIMIT* If you replace your 8 ohm speakers with 4 ohm speakers they will draw more current (x2) from the amplifier. That hurts because with more current comes more heat and heat is kryptonite to amplifiers and most all electronics. A short circuit (bare wire across the speaker terminals) is a resistance, too; a resistance of effectively zero. This will make the current try to go toward infinity. It will succeed only until it reaches the limits of the amplifier’s endurance and at that point the amplifier will die. This will happen more rapidly than you could possibly catch. If you want an example think about how fast a car battery cable will burn to a crisp, conductor and all, if it’s shorted to the car’s frame.

But voltage, current, and resistance are related. So, what happens to voltage when you go from an 8 ohm speaker to 4 ohms? It goes down. This helps because upper voltage is one of the limitations in any power supply. By reducing the voltage demand for a given power output more VOLTAGE head room is available before the amplifier goes into clipping (later, I promise). This Voltage head room is only of use if the amplifier is designed to be rugged enough to handle 4 ohm (higher current) loads. Most are not although most can sustain usable output given reasonable discipline on the part of the owner. You can usually see a notice below the speaker terminals on amplifier’s and AVRs that will state something similar to “Rated for 6 ohm – 16 ohm speakers” If you attach a 4 ohm speaker and play at high levels you will stress the amplifier and risk an overload trip or worse, damage. TAKE CARE when using 4 ohm speakers on non-4 ohm rated amplifiers.

Now we’re getting closer to understanding the complication in answering the original question. We have an idea of what is going on in the amplifier and how it is affected by load (speaker resistance) changes. But what puts limits on power. That’s next – Power Supplies. 

{note: in the following I’ll be using the correct term for speaker load resistance – impedance. Resistance is a term used for DC (direct current) however audio is AC (alternating current) and must include allowances for the effect of frequency on the ultimate value. Each voice coil has a DC resistance specification determined by the wire gauge and the total wire length in the winding but its impedance will vary greatly from this value across its usable frequency range. The 4-ohm/8-ohm designation is a nominal value for the full range that is useful for matching speakers to amplifiers}

The equation wheel in the link from above shows power can be defined as a combination of voltage (V) and current (I). Take either one higher while the other remains the same and power goes up. In every amplifier is a “Power Supply” that converts house current (110VAC [volts AC] 60Hz US and others, 220VAC 50Hz Britain, Europe, and others) into various DC voltages depending on the make and model of the design. (DC stands for direct current in which the current is always flowing in the same direction and AC is for alternating current in which the current switches direction either 50 (Hz) or 60 (Hz) times a second). The components are chosen to withstand a certain limit in terms of current. These current limitations along with the voltage CHOICES combine to establish the power limits of a given supply. At no time can a power supply deliver more total power than is allowed by these constraints without risking damage. That said there are usually two specifications for this. One is the continuous rating. This is the limit for long periods. The other is the dynamic rating. Allowing for brief (<1 sec) bursts of increased output. 

For the most part AVRs and multichannel amplifiers have a single power supply that is shared by all channels. Each channel can deliver voltage UP TO the power supply’s voltage limits and current as determined by the supplied voltage and the load (4 ohm/8 ohm). When the voltage limits are reached the amplifier will “clip”. Clipping effectively flattens off the positive and negative “tops” of the waveforms. This is BAD. Clipping causes the amplifier to run at higher currents for longer (Google: duty cycle) increasing heat. It also creates potentially damaging harmonics that can destroy tweeters. Clipping is to be avoided. Since low impedances make for lower voltages, 4 ohm speakers are inherently less susceptible to clipping than 8 ohm; a plus for 4 ohm speakers. This is the reason amplifiers specify different power into different impedance speakers. The speaker can draw more current before clipping occurs if the amplifier circuit can handle the current. Since the voltage limit is the same and the current is higher – more power.

Before I go on I'll take time for questions - if any. Still to come is Frequency, Fundamentals, Harmonics, Voicing, and THD (Total Harminic Distortion)


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## chinzo

Please go on. Very well written and understandable.


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## tonyvdb

Patrick, just wanted to say that this is very informative and should be made into a dedicated thread that is made a sticky.
Lots of people can benefit from this info :clap:


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## GCG

Is this the correct forum or would another be more appropriate?


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## AudiocRaver

We will create a new thread for it, probably a sticky, I am looking for the best place. In the mean time, continue on assuming it to be an instructional sticky thread, and we can copy/paste it into place when we find it a home.

Thanks again for taking the time, Patrick.


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## GCG

No problem, happy to help.


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## GCG

Before I go on I thought I’d point out a couple of other things involving power and power supplies. I stated that going from 8-ohm to 4-ohm speakers can allow an amplifier channel to deliver more power within the constraints of the designed current limits. I also said that the power supply could only reliably deliver power up to a given limit and when that limit is reached, the power well runs dry. If, as is the case of multi-channel surround sound (5.1, 7.1, etc.), 4-ohm speakers are used for the fronts and 8-ohm speakers are used elsewhere and the fronts end up demanding more power at similar volumes then that dips deeper into the power well leaving less for the remaining speakers. This is easy to do and is in some cases hidden due to the way specifications for speakers are written to tell us how loud a speaker will play. Speaker specifications will usually state this as either Efficiency or Sensitivity. It is measured in db and in this case db is the measure of the Sound Pressure Level or SPL. It’s the same SPL the safety guy at work would measure to determine if hearing protection is required in a given work environment. The sticky point comes with the conditions under which the specification is measured. It’s usually stated by the following:

1 kHz @ 1 Watt @ 1 meter
..or..
1 kHz @ 2.83 Volts @ 1 meter

Meaning they run a 1kHz tone at a power of 1 watt (2.83 volts) to the speaker and measure the SPL from 1 meter away. I prefer the former and here’s why. Assume the conditions above are applied to an 8-ohm speaker. By the equation wheel we can see that for 8-ohm speakers they say the same thing.
Let’s run 1 watt to that speaker and see what voltage develops.

V = √(P*R)
V = √(1*8)
V = √8
V = 2.828427125 ~ 2.83

Now do the same for the 4-ohm speaker.
V = √(P*R)
V = √(1*4)
V = √4
V = 2.00 volts … a 41% difference that gives me an idea of how much headroom I’ll have – db for db.

Now let’s go the other way – let’s apply those 2.83 volts to the 4-ohm speaker and calculate the power being delivered.

P = V²/R
P = 2.83²/4
P = 8/4 = 2 watts … a 2-for-1 difference that betrays the otherwise hidden fact that, db for db, going by this spec I’ll be dipping twice as deep into my power supply well.

To me the first definition is more – apples to apples – than the second. It relates the Efficiency/Sensitivity more directly to the power supply spec of watts which is more useful in my opinion.

Another thing that may be of interest is using the specs to do a little detective work to ESTIMATE the limits of the power supply. I’ll use the specs for my AVR since I have them handy. By my signature you can see that’s a Pioneer Elite SC-71. You can go by the manufacturer’s spec but I prefer using independent lab tests if I can find them as I tend to believe they have less bias. My favorite is Sound and Vision. They did a full review of the SC-71 with a nice lab workup you can find here:

http://www.soundandvision.com/content/pioneer-elite-sc-71-av-receiver-test-bench

First let’s figure out how deep my power supply well is. We see that the power limit into 8-ohms for all seven channels driven (Hey, chinzo, LOOK we’re finally getting to your question – sorta) @1.0% THD (I’ll be getting to that) is 106.8 watts.

106.8 * 7 = 747.6 watts (in the manual the spec is 560 watts – under spec’ing or conservative spec’ing is a good thing to find in a manufacturer in my opinion)

It’s deep enough for me (for now anyway). That’s the power supply total output but what about the voltage limits. When will this thing begin to clip? For that I need to push a single channel (or just two) up to its limit without draining the power supply well. When I find the limits in those conditions I’ll know a little more about upper voltage. Higher speaker impedance yields higher voltages so a limit pushing spec into an 8-ohm speaker is what I’m looking for. And I find it in the first paragraph under the Harmonic Distortion graph. That paragraph reads as follows:



> This graph shows that the SC-71’s left channel, from CD input to speaker output with two channels driving 8-ohm loads, reaches 0.1% distortion at 120.6 watts and 1% distortion at 146.0 watts. Into 4 ohms, the amplifier reaches 0.1% distortion at 204.3 watts and 1% distortion at 247.3 watts.


The spec is most likely to be pushing the envelope at the 1.0% point and beyond so I’ll use that. For 8-ohms that’s 146.0 watts. Again from the equations:

V = √(P*R)
V = √(146.0 *8)
V = √1168
V = 34.18 volts

But that’s RMS and I want the value for peak (I’ll discuss the difference later but peak is where clipping occurs) which is RMS*1.414 which comes to 48.33. So it’s safe to assume the power supply voltage limits are at least +/- 48.33 volts. An estimate of power supply current can now be made by using the max power we found before and this voltage value in our calculations.


*{I have to do an edit here. The power supply peak voltage calculation is mixing RMS and peak values which is a NoNo. }*
*{Corrected using a value of 1057.1 watts peak vs. the 747.6 watts RMS , sorry for the mix up.}*
I = P/V
I = 1057.1/48.33
I = 21.87 amps peak or 15.47 amps RMS

Just for grins let’s calculate the voltage using the specs for a 4-ohm speaker. At 1.0% distortion the channel was pumping 247.3 watts.

V = √(P*R)
V = √(247.3 *4)
V = √989.2
V = 31.45 volts RMS or 44.47 volts peak

That’s less than what was calculated for the voltage limit for the power supply and we haven’t reached the power supply max power limit so the best safe assumption is this limit is driven by the current limitations of the amplifier stage itself.


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## GCG

I went searching for examples of speaker manufacturers that use the 2.83 volt spec for Efficiency/Sensitivity with a 4-ohm speaker and found this right away on the PSB site.

(1W (2.83V) @ 1M, IEC-Filtered pink noise, C-weighted)

!!! Into a 4-ohm Speaker !!!

Bad PSB!!! Bad!!! no biscuit.

We just showed that 1 watt into a 4-ohm speaker yields 2 volts and 2.83 volts will yield 2 watts. This shows one of four things about a manufacturer.


They don't know what they're talking about. (unlikely, after all, they do MAKE speakers)
They want to confuse you. (I doubt it)
They left the writing of the spec sheet to an under-informed noob. (possible)
Nobody proof read the spec sheet before it was published. (most likely)

There is no way to know what the real conditions were to establish this spec. This alone might cause me to take a speaker off my short list.


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## AudiocRaver

GCG said:


> I went searching for examples of speaker manufacturers that use the 2.83 volt spec for Efficiency/Sensitivity with a 4-ohm speaker and found this right away on the PSB site.
> 
> (1W (2.83V) @ 1M, IEC-Filtered pink noise, C-weighted)
> 
> !!! Into a 4-ohm Speaker !!!
> 
> Bad PSB!!! Bad!!! no biscuit.
> 
> We just showed that 1 watt into a 4-ohm speaker yields 2 volts and 2.83 volts will yield 2 watts. This shows one of four things about a manufacturer.
> 
> 
> They don't know what they're talking about. (unlikely, after all, they do MAKE speakers)
> They want to confuse you. (I doubt it)
> They left the writing of the spec sheet to an under-informed noob. (possible)
> Nobody proof read the spec sheet before it was published. (most likely)
> 
> There is no way to know what the real conditions were to establish this spec. This alone might cause me to take a speaker off my short list.


Not sure what model you pulled up. I glanced at the Imagine T3 and T2 Towers...

The Imagine T3 Tower is nominal 8 ohms, minimum 4 ohms, and they specify the rms test voltage as you have shown for the sensitivity. The Imagine T2 Tower is nominal 6 ohms, minimum 4 ohms, and they conveniently left out the rms test voltage. Do you remember which model you looked at? Just curious.


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## GCG

The Synchrony One. $2300+ Each at BestBuy scratch and dent. Here's the spec sheet.

http://www.psbspeakers.com/content/130129092905-13-014_PSB_Synchrony_One_English_Specifications.pdf


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## GCG

Looks like they have moved away from 4 ohm designs. Granted it's an obsoleted product but it highlights the need to be vigilant in your research.


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## AudiocRaver

Yep, they definitely messed up on that one. Like you say, you almost have to be smarter than them, exactly the point of your primer.


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## istvan

Looks like all channels driven at 100W with .02% distortion in this post  . Unless you can afford http://www.krellonline.com/multi-channel-amps_ARCHIVE.html Check out the power supply BTW.


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## GCG

This weekend is loaded up with seasonal events. We've already been to two parties and a church outing to see an IMax documentary on Jerusalem. We have another party we've been invited to tomorrow. If I can find time tomorrow I'll try to get the next post of the Primer in.


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## GCG

… Somebody gimme an “A” …

Odd way to start a post but it’s an excellent way to dovetail into a discussion of Frequency, Harmonics, Voicing, and THD (Total Harmonic Distortion). The phrase is a way of asking anyone in the area to play the note “A” above middle “C”. It’s often used to help a musician or singer to get to a familiar key before proceeding to play, sing, or tune an instrument. In response someone would play the note that causes vibrations in the air at 440Hz. That’s what A above middle C is. A above high C is 880Hz. There’s a whole plethora of A’s in the human hearing range staring with 27.5Hz, followed by 55Hz, 110Hz, 220Hz, 440Hz, 880Hz, 1760Hz, 3520Hz, 7050Hz, and 14100Hz. Of course these are Frequencies. Hz is an abbreviation for Hertz which is measured in cycles per second, the number of pulses of air pressure per second at the ear. 

But isn’t 440 cycles per second, 440 cycles per second? If so why does it sound different when it’s played on piano as opposed to a violin? That’s where harmonics come in. See, the 440 cycles per second is the fundamental. That’s the primary frequency being played. But each instrument will also throw off several more frequencies that are multiplies of the fundamental. Yup, all are A’s. What separates a piano from a violin or from a flute or from a Fender Telecaster playing through a Marshal Tube Amp is the distribution of this compliment of harmonics and their intensities. The following image may make it more clear.










This is taken from a pretty good treatment of the subject of the physics of sound and music from Eastern Illinois University. It goes into more depth if you're interested.

http://castle.eiu.edu/~ddavis/chapter_12/ch12.htm.

The harmonics thrown off by a particular instrument make up its voice.

What you need to take away from this is that not that harmonics are bad; just the wrong harmonics. If the harmonics aren't correct our brains know and this takes away from the illusion of realism. This deviation is called Harmonic Distortion. The measure of the total amount of deviation from correct harmonic content across the whole spectrum is Total Harmonic Distortion and is measured in percent. Federal standards require manufacturers to make power specification measurements at a THD (Total Harmonic Distortion) of 1%. Most audiophiles find this to be a little high, most preferring numbers at or below 0.1%. The standard, however, gives the buyer the opportunity of comparing various offerings on a level playing field.

That's all on this. One more to go. Human Capacity in hearing. This an often ignored subject that in my opinion would halt a great many debates before they start.


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## GCG

As promised the last instalment in the basic discussion is human capacity. This is bound to spark some degree of controversy but it’s important, at least in my opinion.

Every so often on this and other forums dedicated to upper end audio will be the inevitable topic discussing whether this or that whiz-bang device makes an audible difference. What follows is invariably a long heated discussion on what can and can’t be heard, numerous quotes of various “reputable” reports, scientific papers and magazine articles. Each poster will be doing his or her best to sway the group opinion to their understanding of the truth. I get drawn in from time to time but afterward usually regret doing so because sooner or later I’m brought back to a belief I’ve held for a long time.

Most of the very opinionated posters are right, even though their opinions are often diametrically opposed to each other and it has to do with each person’s own physical capacity when the critical limits of the human senses are concerned. We’re all different and some (sometimes it seems like most) don’t want to recognize it. I’ll use myself and color vision as an example.

I’m partially colorblind, not completely, just partially. I don’t have a problem with red and green at a traffic light but get too shades of either one too close together and I’m lost. It has been the source of great frustration for my wife when picking paint colors at Lowes or Home Depot. She wants to get the shade just right for the kitchen or bedroom or wherever and she narrows it down to a couple of paint chips and asks me what I think. All I can do is put on my most innocent face and shrug because to me they’re both the same color. This is where she gets disgusted, mentions that I’m no help, and picks one herself. We’ve been married 31 years now and she doesn’t ask me anymore.

I know there are similar differences in hearing. I know because I was enlisted Navy and they gave me the sonar tech hearing test while I was in basic training and the same thing happened. I couldn’t be a sonar tech. I didn’t have the critical hearing capacity it took. However this I later discovered was the rule not the exception as was the case for my color vision. It seems that only a minor percentage of those tested can qualify. It involves two major categories; low volume sensitivity and fine frequency discrimination. It’s mostly genetic but if you have the innate talent it can be further developed. After several years the Navy has decided that attempting to develop the needed skills without the innate ability is largely a waste of time and resources so they don’t try.

In the forum discussions about this or that issue that’s supposed to make an audible difference the answer may not be psychoacoustics or a willingness to let yourself “believe” that you’re actually hearing something when you are not. Some, a select few (lucky or not may be a matter of finances) may have the actually capacity to hear the difference between two very low levels in THD or a faint improvement when using special interconnects. If so this could be augmented if that person’s vocation involves critical listening skills. I couldn’t say either way because I DON’T have that ability and I have the test scores to prove it.

What to take away from this is that you should make your purchases according to your own capacity based on in store listening tests. I like to start with the top of the line and work my way down. It is a well-documented trait that we seem to prefer the more recent of two compared items in listening tests assuming there isn’t any real audible difference. By starting at the top I use that to let me know for sure when I get to a price range that is noticeably inferior to my ear. I go back up to the next price point and try to break it down from there. After that it’s an issue of feature as opposed to function. I could have gotten away with the Pioneer Elite model that was priced one step lower than the SC-71 had it not been for the fact that I needed 4-ohm capability (my Infinity RSb’s are 4-ohm) so I had to go up one notch to get that.

One last thing, get the system that YOU will enjoy. Don’t buy something to impress someone else. If that’s the goal just take the price you’d be willing to pay for the system in fresh crisp $100 bills and make some art to hang on the wall. You’ll get the same reaction. The object of your efforts will walk into the room, see the study of Benjamin’s on the wall, say “Ooo, Ahh” in a very impressed tone and then walk out. If you go the artwork route, you’ll still have your cash.


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## willis7469

GCG, I've been following this for awhile with great interest. Thank you for your anecdotes, and great technical knowledge. I wanted to tell you I was laughing out loud at the humble matter of fact way you shared, " I couldn&#146;t say either way because I DON&#146;T have that ability and I have the test scores to prove it." I agree that buying gear for the sake of others opinions/impressions, etc, is a waste. Fwiw, I'm of the opinion that all I can hear, can't necessarily be measured, and all that can be measured, can't necessarily be heard. 
Please continue!


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## GCG

I think this will do for now. Unless there are questions or suggestions. This topic isn't mine and this primer was done with the OP's permission. If the primer portion is transferred to another thread then I'd be more than happy to add to as my knowledge and time permit.

Thanks for the kind words.


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