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post #1 of 46 Old 10-30-2012, 06:50 AM - Thread Starter
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I am going to buy a new receiver for my home theatre. I read up on some info but a little confused. When you say all channels driven does this mean that a 140 watt amp all channels driven is 7 separate 140 war amps so each amp would take care of each speaker individually.

also most pioneer Elite receivers now say 140 watt per channel. is this the same. I don't want the signal to be spread across all the amps I want each amp to power each speaker individually.

Then the new pioneers speakers say the they were tested at 1k instead os 20hz-20k like the older Elite receivers. I thought the 1k thing was a gimmick. I want the best sound quality

thanks
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post #2 of 46 Old 10-30-2012, 07:43 AM
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140wpc is not all channels driven, when you see it on a receiver's specs.
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post #3 of 46 Old 10-30-2012, 08:09 AM
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The large manufacturers who sell in places like best buy all generally use a 2 channel driven number. It's what you would get if you listened in stereo. Some use a 1K signal, some use 20-20k. It's not as bad as it sounds since you'll rarely drive all 7 channels full at the same time.

Having said that, I would ignore the wpc numbers. It seems like the manufacturers can specify any number they want. If you want a good idea of the power a receiver can deliver, look on the back and look at the power supply number. Even then, not all power supplies are measured the same, but it's still a better number to look at.
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post #4 of 46 Old 10-30-2012, 08:34 AM
 
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i think 1khz tone compared to 20hz - 20khz noise is a really rude difference if the fluctuation is high.
a simple test tone is simple .. and if the watts go down a large portion because the tone becomes more complex .. well i'm sure there are regulations determining how much fluctuation is possible.
because that is the difference when listening to voices in a movie, and they are really loud, and then suddenly everything isnt as loud because there is background music or an action scene.

but that is what it boils down to.
you could always play music and a test tone on top of it.. and if the test tone is always louder, then principles are loose .. and reference is further away.

it gets ugly compared to a person calibrating an equalizer with a sine sweep compared to a person calibrating with pink noise.
that person would need to do both and find the average between the two to get the whole system response calibrated with an average.
that way the small things that are extra loud are also calibrated compared to the complex sounds of a wider frequency range.

but i dont think it really exists much.
from what i've seen, the trend seems to be allowing the additional charge inside the capacitors boost the stereo output while lowering the distortion percentage .. and then as those capacitors start to drain because more speaker channels are being used, the number of watts gets lower and the distortion percentage goes up.

if people modify their amplifier to bring the distortion number down when playing surround sound.. then likely the number of watts in stereo will also go up.
it is because of the speaker channels sharing the same capacitors, or because there are different 'modes' for the voltage rail feeding those capacitors when in stereo or surround sound mode.

that mode switch might be a clock difference, or a voltage difference, or maybe something to do with voltage or clock going to the preamp inputs.
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post #5 of 46 Old 10-30-2012, 08:47 AM
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A typical receiver with that kind of specs actually has a power supply good for a total of 500 watts or so of DC power.

That means that after you subtract 100 watts or so for the various receiver circuits, there is maybe 350 watts left over for the amplifiers.

That means you can run TWO channels at 140 watts each, or 7 channels at 50 watts each.

7 channels is stretching the available power very thin. I would stick to 5 channels with most of those receivers and not try to run 7.

Many people add an amplifier to the front 2 channels to get more total power; this leaves the receiver less channels to run and makes a big differernce.

The catch is that not all receivers have preouts available for the front channels to do this.
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post #6 of 46 Old 10-30-2012, 08:58 AM
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There is a relatively easy way to get an idea of what an AVR / amp can deliver, if driving all channels at once.
Take the max power spec of the power supply and divide it by 2 and divide it again by the number of channels.

Example:
max power (power supply): 1100 Watt
efficiency of the power amp (i.e. Class AB): ~50%
number of channels: 7
Results:
1100 / 2 / 7 = 78 Watt / channel (seven channels driven)
1100 / 2 / 9 = 61 Watt / channel (nine channels driven)
This usually holds true for number of channels beyond 4.

At the other end the current handling capabilities of the output transistors used are the limiting factor, thus
1100 / 2 / 2 = 275 Watt / channel (stereo) is NOT the max power available because the current capabilities of the output transistors is limiting this to the manufacturer stated max power, i.e. 140 Watt / channel (stereo).
This is normally stated in the specs section of the manual.

For other types of amps like Class G or H or Class D the efficiency factor will be somewhat better, but this depends on the individual design of the power amp circuitry.
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post #7 of 46 Old 10-30-2012, 12:12 PM
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EZ to calculate...
Today most AVRs are rated @ 2 channels driven into 8 Ohms.
For example if the AVR is 100W x 2, 200W total simply divide the 200W by the # of channels.
  • For 5 channels, the power is 40W per channel (200W divided by 5)
  • For 7 channels, the power is 28.5W per channel (200W divided by 7)


The AVR has only so much power voltage/current capability. Note that the above example was for power output specs into 8 Ohms, for determining power output into lower loads such as 4 Ohms.
Totally different calculation as most AVRs are built for lower cost so its power supply voltage/current capability will be significantly decreased and the brand will likely incorporate some type of limiter to keep the AVR from self-destructing..


Just my $0.02... wink.gif
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post #8 of 46 Old 10-30-2012, 01:27 PM
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Quote:
Originally Posted by Joji View Post

I am going to buy a new receiver for my home theatre. I read up on some info but a little confused. When you say all channels driven does this mean that a 140 watt amp all channels driven is 7 separate 140 war amps so each amp would take care of each speaker individually.
also most pioneer Elite receivers now say 140 watt per channel. is this the same. I don't want the signal to be spread across all the amps I want each amp to power each speaker individually.
Then the new pioneers speakers say the they were tested at 1k instead os 20hz-20k like the older Elite receivers. I thought the 1k thing was a gimmick. I want the best sound quality
thanks

First of all, any multichannel amplifier indeed has multiple amplifiers, each connected to it's own speaker outputs. There is no way in our phyusical universe for a single power amplifier to accept multiple different inputs and output them to different places. It's a one-in-one-out proposition for the power amp. Power output depends on a number of factors, including the capability of the output amplification devices (transistors in this case) and as indicated above the power supply available. Let's assume a pair of transistors in push pull for each separate amp. A pair that is specified by their manufacturer to be able to make 100 watts at X distortion can only do so when they have the appropriate cpower available to them. So if I take a 100 watt output transistor set and connect it to the power supply of a preamp that needs to deliver a mix of 2 watts or so, the power transistors will not be able to hit 100 watts. The reason a lot f receivers cannot output full 2 channel rated power into 5 or 7 channels is their power supplies just aren't robust enough to serve all those amps at onece WHEN THEY CALL FOR FULL POWER. Using movies as an example, the "typical" dialog level of 85 dB at reference requires, and will use only, 1/100 of the power needed to play back peaks (105 dB per speaker).

Generally modern receivers use the exact same output devices for every channel. FTC rules establish how to determine power and because of a quirk in the wording, multichannel amps need only be able to hit ther specified levels with 2 channels driven, most manufacturers figure. So that's what you should expect.

If the specification says 100 watts per channel at 1% distortion, all channels driven, it mearns, really, that the MFR says the amp can make 100 watts through each amp all at the same time. You don't see receivers specified this way and third party testing shows they are absolutely all over the place as to how much of their rated power they can hit with multiple channels operating, or at lower impedance (which stresses the output devices more . . .)

So with a typical receiver, if the program material every actually maxed out in all channesl at once (and you needed full 2-channel rated power to hit those levels) you would get significant distortion, and probably not the full 140 watts or whatever from any channel (and you don't really want to listen to 140 watts at 10 or 15 % distortion unless it's a distorted electric guitar and you're a goodly distance away from the speakers). But real world movie material doesn't (so they say) peak in all channels simulteneously, so it is not as big an issue as it might seem at first glance. Many of us (like me) listen at lower than reference levels, requiring significantly less than full power even for the loud parts.

But really the only way to know the output capability of any of these devices is to test them yourself (something I could not do) or read independent third party testing. There are too many variables that the manufacturer can fiddle with to goose up their power ratings. They do that because it's what sells, and beccause it's what everybody else does and it's hard to educate consumers that "my 50 wpc all chanels driven is superior to brand X's 120 wpc, 2 channels driven." Easier just to play the game the way it is played.
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post #9 of 46 Old 10-30-2012, 01:39 PM
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Home Theater Magazine shows the most popular models bench tested so if your interested in knowing it will give you an idea of what to expect so far the pioneer Elites with D3 amps put out a nice solid number in 7 channels driven.
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post #10 of 46 Old 10-31-2012, 12:15 AM - Thread Starter
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Here is a example. This is a older Elite unit

VSX-74txvi

http://www.pioneerelectronics.com/PUSA/Home/AV-Receivers/Elite+Receivers/VSX-74TXVi

This says 140 watts x 7 (20hz-20hz @8ohms) 0.09 % thd

Is this 7 individual amps 140 each to make it all channels driven. So if a movie plays with a big explosion the audio will only strain the speaker it was mixed for. Example surround backs.
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post #11 of 46 Old 10-31-2012, 07:28 AM
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Quote:
Originally Posted by Joji View Post

Here is a example. This is a older Elite unit
VSX-74txvi
http://www.pioneerelectronics.com/PUSA/Home/AV-Receivers/Elite+Receivers/VSX-74TXVi
This says 140 watts x 7 (20hz-20hz @8ohms) 0.09 % thd
Is this 7 individual amps 140 each to make it all channels driven. So if a movie plays with a big explosion the audio will only strain the speaker it was mixed for. Example surround backs.

There are 7 amps (or else it could not under any circumstances ever feed 7 separate channels because one amp can only handle one channel) each of which likely could do 140 watts. Any two of which probably could do 140 watts. But I would not take that spec to mean "all channels drivern," because that's not what it says. Power required will be whatever it is. With efficient speakers and a close listening position you might not even need 100 watts to hit reference in any given channel. But when power requirements go up, they go up in the channel(s) with the louder sound, if that's what you're asking at the end there.
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post #12 of 46 Old 10-31-2012, 07:38 AM
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Quote:
Originally Posted by Joji View Post

Here is a example. This is a older Elite unit
VSX-74txvi
http://www.pioneerelectronics.com/PUSA/Home/AV-Receivers/Elite+Receivers/VSX-74TXVi
This says 140 watts x 7 (20hz-20hz @8ohms) 0.09 % thd
Is this 7 individual amps 140 each to make it all channels driven. So if a movie plays with a big explosion the audio will only strain the speaker it was mixed for. Example surround backs.
Contrary to all the incorrect information in the thread... This particular unit was tested and it put out more power than all the nonsense formulas other posters would have predicted.
Quote:
Driving all seven channels into 8Ω, the Pioneer delivered 63Wpc at 20Hz and 136Wpc at 1kHz (to the nearest watt) before clipping (1% THD+noise). This test was repeated several times with approximately the same result, and the unit went into protection on each run after a reading was obtained. But it recovered after a few seconds when the input signal was removed. The limited power at 20Hz with all channels operating did not affect the listening tests (using full range left and right speakers). This was likely due both to LEU's relatively small room and the fact that multichannel film sound rarely stresses all channels simultaneously with a very low frequency signal.

That said, an all channels driven sine wave test is not a realistic test of real world use of a receiver.
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post #13 of 46 Old 10-31-2012, 07:49 AM
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Yep, I read that link. But that makes me question what HT is doing to measure. That unit has a 530W power supply and even if you assume 100% efficiency of the power supply and all that power going only to the power amps, the figures just don't add up.

Divide 530W by 7 and you get a max of 75.7 wpc! What law of physics has changed to make that possible? I even read another HT review of a unit with a less than 300w power supply that claimed tested at 60+wpc with all 7 channels driven.

Personally I just don't believe it.

Lloyd
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post #14 of 46 Old 10-31-2012, 08:09 AM
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^^^

capacitance doesn't hurt... wink.gif

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post #15 of 46 Old 10-31-2012, 08:13 AM
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In what way is capacitance going to be enough for any appreciable length of time, going to make a whit of difference? Yeah, for a short burst you might say that, but certainly not for an extended length of time, and by extended I mean a few minutes.

Lloyd
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post #16 of 46 Old 10-31-2012, 08:19 AM
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^^^

if you look at the tests, most of them will end up going into protection when pushed... and also, several of the tests on units (such as certain amplifiers that are very popular around here) show that they will only produce their "tested acd numbers" for very short periods of time...

in the "real world", you'd never push the amplifier to "full power" for anything longer than a short burst... acd tests are one of the most misused and misunderstood tests that exist... while they do tell you "something", they don't tell you what many think they do... "real world sound" is dynamic....

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post #17 of 46 Old 10-31-2012, 08:27 AM
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I won't argue the point, but I do agree with your conclusion.

I use their test results to see their overall impressions and subjective results. And I know that a bunch of power isn't necessarily all that big a deal. My Denon 2113ci pushes out about a true 50wpc from my calculations, but because of the Audyssey EQ, I find myself playing at much lower levels than I was used to. Not uncommon at all for me to play at -30 to -40 db during the day, and pushing up to no more than -20 for even the loudest.

Most of their power ratings from testing fall into math made simple range, it is only on some few boxes have I seen them test wpc at greater than power supply ratings.

Lloyd
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post #18 of 46 Old 10-31-2012, 08:41 AM
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well, at least we agree on the conclusion... smile.gif

c'mon man... turn it up!!! biggrin.gif

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post #19 of 46 Old 10-31-2012, 08:54 AM
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Quote:
Originally Posted by lparsons21 View Post

In what way is capacitance going to be enough for any appreciable length of time, going to make a whit of difference? Yeah, for a short burst you might say that, but certainly not for an extended length of time, and by extended I mean a few minutes.

If the measurements you find unbelievable are for a few cycles, not a few minutes, then your objection is to the testing methodology, not impossibility. Except perhaps with hypercompressed music, which hopefully nobody listens to at 120+dB average, real world content will typically only require very short bursts for transients. From some recent reviews of bass gear, for example, it looks to me like the initial transient of a plucked bass guitar note is half a cycle (hard to really tell at what frequency but even if it's 20 Hz that's 1/40th of a second) and about 10 dB above the beginning of the ringing of the note. So while it's possible the HT measurements exaggerate by a factor of, maybe 2 or so, they are of real potential importance.

FWIW, from a Stereophile review of a Boulder amp

"Although hardly the arc welder of a 100 lb Krell, the 500AE's power supply isn't exactly a featherweight. With a 6"-diameter, 3"-thick toroidal power transformer and 74,000µF of storage capacitance per channel, the amp has a claimed peak current capability of 50 amperes, and is designed to be able to deliver that current for up to a tenth of a second before supply depletion starts to set in."

At DC, 50 amps into 8 ohms is a theoretical 20 Kwatts, 14Kwatts RMS if you assume that's the peak of a sine wave. . Just not for long. Of course the signal doesn't stay at the peak for long, either, so the caps are recharging essentially constantly. The amp itself is specified at 150 WPC at 8 ohms . . .
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post #20 of 46 Old 10-31-2012, 08:54 AM
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Quote:
Originally Posted by Stereodude View Post

Contrary to all the incorrect information in the thread... This particular unit was tested and it put out more power than all the nonsense formulas other posters would have predicted.
That said, an all channels driven sine wave test is not a realistic test of real world use of a receiver.

Contrary to what has been stated rolleyes.gif these units have been actually tested just a few weeks ago (issue 10/2012 audiovision magazine) with 7 channels driven:

Onkyo TX-NR5010: 7 x 78 Watt / 8 Ohm / 7 channels driven
Marantz 7007: 7 x 70 Watt / 8 ohm / 7 channels driven

Strangely eek.gif enough the numbers are almost identical what could have been calculated beforehand by the specs and some basic knowledge about electronics design ...
If this test is realistic or not does not really matter at all, because it is a worst case test and delivers valuable information and (measured) numbers as a basis for comparison.
This gives some inside about the capabilities of the power supply and the power amp section.
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post #21 of 46 Old 10-31-2012, 11:16 AM
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Quote:
Originally Posted by lparsons21 View Post

That unit has a 530W power supply
First, how do you know it has a 530W supply? Second, what does that 530W rating mean? Under what conditions is it 530W?
Quote:
and even if you assume 100% efficiency of the power supply and all that power going only to the power amps, the figures just don't add up.
Electrical design is not as straight forward as you're trying to make it. They figures don't have to add up in the manner you're trying to make them.
Quote:
Divide 530W by 7 and you get a max of 75.7 wpc! What law of physics has changed to make that possible? I even read another HT review of a unit with a less than 300w power supply that claimed tested at 60+wpc with all 7 channels driven.
No law of physics are being broken.
Quote:
Personally I just don't believe it.
Then don't. The measurements are very likely correct for the method they used to test.
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post #22 of 46 Old 10-31-2012, 11:21 AM
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Quote:
Originally Posted by gurkey View Post

Contrary to what has been stated rolleyes.gif these units have been actually tested just a few weeks ago (issue 10/2012 audiovision magazine) with 7 channels driven:
Onkyo TX-NR5010: 7 x 78 Watt / 8 Ohm / 7 channels driven
Marantz 7007: 7 x 70 Watt / 8 ohm / 7 channels driven
What's your point? That some general formula based on an arbitrary power rating on the back of a piece of electronics gear might be right occasionally?
Quote:
Strangely eek.gif enough the numbers are almost identical what could have been calculated beforehand by the specs and some basic knowledge about electronics design ...
And yet they're not always right. Which is why people actually measure the amps rather than read a number off the back and plug it into a formula.
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post #23 of 46 Old 10-31-2012, 11:30 AM
 
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here's a little fun fact..

120 volts from the wall
20 amps (if the circuit breaker doesnt pop)
amounts to 2,400 watts available.

most of the power supplies look like they are step-down transformers (voltage reduction) .. and nothing has yet been said about step-up transformers (voltage increase).
car audio amplifiers often use the step-up coil to raise the incoming voltage to a higher number.


the question of engineering is..
does the amplifier suck up all of the electricity from the wall .. or does it make it's own electricity to save on the electric bill ?

kinda makes me wonder about some of the amplifiers in the $2,000 - $5,000 range.
are they putting all their effort into lower distortion and higher slew output, or did they also help save some money on the electric bill ?
one might think stepping down doesnt allow any room for savings because even if you stepped down less to get more voltage into the amplifier, the voltage comes from the wall.
but that doesnt say anything about the amperage coming from the capacitors inside the amplifier, and those capacitors refilling from the voltage coming in.. compared to refilling with amperage and needing to suck on the power supply more, causing a larger use of electricity.


lets not sell chemistry short.
to say 12 volts coming in cant produce 16 volts out simply says mother nature isnt sophisticated enough to let such a situation exist .. when in fact she is.


**edit**

i think the real thing to be upset about is not knowing how these wattage numbers are being tested for.
sure does look a bit helpful to think they specifically say a 1khz tone was used to get the number of watts.

what does the 'noise' stand for in 'total harmonic distortion + noise' ?
how does that test get done?
a simple 1khz test tone doesnt have harmonics.

i think all of the tension will come to shed some light on any situation where a person looks at the number of watts, brings the amplifier home and installs it, then what?.. the amplifier has different volume fluctuations throughout the length of a movie?

what are we talking about?
all the number of things that could be different between one amplifier and the next?
signal to noise ratio and distortion wasnt enough .. or in the near future it simply wont be enough? (i could see this happening)
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post #24 of 46 Old 10-31-2012, 11:39 AM
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Quote:
Originally Posted by Stereodude View Post

First, how do you know it has a 530W supply? Second, what does that 530W rating mean? Under what conditions is it 530W?
Electrical design is not as straight forward as you're trying to make it. They figures don't have to add up in the manner you're trying to make them.
No law of physics are being broken.
Then don't. The measurements are very likely correct for the method they used to test.

1. I downloaded the brochure and the picture of the back of the amp showed 530W consumption

2. Means that is what the unit consumes, I assume that is max.

Yeah, I know electrical design isn't that straight forward, I've only been working in the field since the early 60's. And yeah, the figures don't have to add up unless you are considering steady testing for a length of time well past the 'burst' period. And it seems that the testing is very much more like a burst than anything else.

But I've said I'm not going to argue the point. And frankly it doesn't matter as with the room I have this stuff in will be the room they drag me out toes up from, almost any of this stuff will blow the walls out!! smile.gif

But here's a trick. If I do my figuring the same way on all the gear I look at, the results will be correct in relation to each other.

Lloyd
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post #25 of 46 Old 10-31-2012, 11:57 AM
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Originally Posted by lparsons21 View Post

1. I downloaded the brochure and the picture of the back of the amp showed 530W consumption
2. Means that is what the unit consumes, I assume that is max.
It is definitely not the max possible consumption or the S&V results wouldn't be possible. I'm not sure if UL has any standards for that rating. AFAIK, It pretty much just means that under some set of conditions the unit draws that amount of power.

For example, in the big Peavey IPR thread JD (the designer) swore that his IPR amps could deliver their rated power even with sine waves and had personally tested them under such conditions. However, the IPR 1600 has a 400W power draw number silk screened on the back, yet per the designer it can deliver 1000W+ continuously into sine waves (not burst). At least in this case its pretty clear the 400W number doesn't really mean anything in terms of real max power output.
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Yeah, I know electrical design isn't that straight forward, I've only been working in the field since the early 60's. And yeah, the figures don't have to add up unless you are considering steady testing for a length of time well past the 'burst' period. And it seems that the testing is very much more like a burst than anything else.
Sound & Vision (or whatever they're called now) didn't state a duration for their ACD test, so that's not helpful but based on their text I didn't get the feeling that it's a 10ms burst either.
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But here's a trick. If I do my figuring the same way on all the gear I look at, the results will be correct in relation to each other.
That's true. However, I wouldn't feel confident comparing different magazines or reviewers ACD test results unless there was a comprehensive test methodology write up for each to ensure they were actually equivalent.
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post #26 of 46 Old 10-31-2012, 12:03 PM
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Originally Posted by anwaypasible View Post

here's a little fun fact..
120 volts from the wall
20 amps (if the circuit breaker doesnt pop)
amounts to 2,400 watts available.
Your fun fact isn't so cut and dry. Can I source a 3600W from that circuit? If so, how long can I draw 30A before popping the breaker?
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post #27 of 46 Old 10-31-2012, 12:17 PM
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^^^

heh... introducing "how things really work" back into the conversation, instead of "scienc-y sounding stuff", i see... wink.gif

the response should be interesting...

- chris

 

my build thread - updated 8-20-12 - new seating installed and projector isolation solution

 

http://www.avsforum.com/t/1332917/ccotenj-finally-gets-a-projector

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post #28 of 46 Old 10-31-2012, 12:17 PM
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I always thought trasformers were measuring RMS power. The voltage is a 60Hz sine wave and the RMS number is something like 70% of the peak value. I think that gives the average rate of energy consumption over the period of time for the sine wave. Also, transformers can, for short periods, deliver alot more power than the RMS value. As long as the coils have time to cool, it's OK to push them over the limit for a brief period of time. It's been a long time since I took any EE classes, but that's the way I remember it.
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post #29 of 46 Old 10-31-2012, 01:02 PM
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Quote:
Originally Posted by Stereodude View Post

Your fun fact isn't so cut and dry. Can I source a 3600W from that circuit? If so, how long can I draw 30A before popping the breaker?

The circuit beaker specifications are straight-forward..
Provided the product is certified by UL/CSA.
For a 20 Amp breaker, assuming the correct wire of either 10 or 12 guage is used.
The time limits @ 20 Amps for tripping the breaker the upper is 100 seconds and lower is 10 seconds. If the load is 30 Amps (50% above spec) then the upper limit is 50 seconds and lower limit is 5 seconds..

Next question.. rolleyes.gif

Just my $0.02... wink.gif
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post #30 of 46 Old 10-31-2012, 01:13 PM
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Quote:
Originally Posted by M Code View Post

The circuit beaker specifications are straight-forward..
Provided the product is certified by UL/CSA.
For a 20 Amp breaker, assuming the correct wire of either 10 or 12 guage is used.
The time limits @ 20 Amps for tripping the breaker the upper is 100 seconds and lower is 10 seconds. If the load is 30 Amps (50% above spec) then the upper limit is 50 seconds and lower limit is 5 seconds..
Next question.. rolleyes.gif
Wait, you mean I can draw considerably more than 2400W from a 20A 120V circuit for short durations!?!?! How can that be? There's only 20A available!!

ps: way to miss the obvious point I was making. rolleyes.gif
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