Question on bi-amping - Page 25 - AVS Forum
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post #721 of 1044 Old 11-27-2013, 05:53 PM
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Originally Posted by amirm View Post

You mean the 13.6? If so, they are the voltages per division (gray grid) so you can visually determine what the voltage is.

Ok thanks. So by that determination, this statement below is uninformed (at best)?

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Originally Posted by arnyk View Post

Also, the difference in power output of the 2 channels is still only about 1 db which is barely audible at the very best.


So then I assume you made this below observation based on correct facts?
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Originally Posted by amirm View Post

The peak to peak voltage of the tweeter amp is nearly 20% higher than the woofer amp.

And what would you consider to be the dB difference from a 20% voltage difference?
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post #722 of 1044 Old 11-27-2013, 06:13 PM
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Originally Posted by amirm View Post


All I want you to agree is this statement is false that you made in the parallel thread:
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Originally Posted by arnyk View Post

With passive biamping the input to the amps is the same and their gain is the same, then the output voltage is the same. There is no active crossover to route the signals. The tweeter amp is not isolated from the woofer signal. Both amps amplifiy both the woofer signal and the tweeter signal.
Clearly that statement is based on paper amplifiers that have constant final stage power supplies.

The standard electrical engineering term that you are looking for Amir is "Constant voltage power supply". While it may seem to be a nit to the non-engineers reading this thread, it is actually very critical because the two standard extreme cases are constant voltage and constant current and "constant final stage power supplies" is clearly neither or both, IOW nonsense.
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As I am showing above and have repeatedly said, the power supplies almost always are variable voltage and that voltage depends on current.

A trivial observation.
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Since there is no way at 20 Hz for woofer and tweeter to be drawing the same current at that frequency, then the voltages will not be the same.

Another trivial observation.

Obviously Amir you have zero experience with real world circuits and have no concept of engineering because you are obsessing over nits. Nothing in the real world is exactly constant voltage or constant current. You are trying to make a federal case out of that simple well known fact.
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Finally, your comments about audibility are once again invalid. We don't care about pure sine waves for audibility of amplifier distortion. We care about real music and movie sound.

Amir how can you say that? The very statement "We don't care about pure sine waves for audibility of amplifier distortion. We care about real music and movie sound. " is nearly a word-for-word quote of what I have posted on AVS almost every day for the past 4 months or more. Here is an example:

http://www.avsforum.com/t/1489866/sensitivity-and-resistance#post_23718314 (I9/9/13)

"
There is one thing about load ratings that needs to be borne in mind is the fact that sine waves are commonly used for testing, while music is generally used for listening. Sine waves are very different from music in a critical area and that is crest factor. Crest factor is the ratio between the peak and average voltage of a signal. Sine waves have a crest factor of 3 dB. Music has a crest factor of from 6 dB to 20 dB. Signals with a higher crest factor make fewer demands on amplifiers, especially the transistor heat sinks, power transformers, and to a lesser degree (IOW you need similar parts no matter what the crest factor is) filter capacitors.

Therefore an amplifier that would overheat on the test bench while driving a test load resistor of say 4 ohms and while playing sine waves, will be capable of playing without overheating if we change from sine waves to music. I've actually done this experiment, and theory equals practice.

The crest factor of music means that an AVR that can operate 2 channels at a certain power level and laod impedance with sine waves, may be able to operate 7-8 channels with music
"

This appears to be a blatant attempt to steal my words and make them your own. ;-) Foul!

Quote:
And further, we cannot assume yet again ideal paper amplifiers. I will write on this more later. But if you are going to comment, please explain the shape of the clipping in the woofer amp. Why is it not perfect flat-topped?

Obviously the real world circuit under test is not ideal. That apparently surprises you!

(shaking head)
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post #723 of 1044 Old 11-27-2013, 06:20 PM
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Quote:
Originally Posted by arnyk View Post

You are trying to make a federal case out of that simple well known fact.

Well known! To who?

Labelling it as trivial is your only recourse. I guess that makes sense since you make observations based on flawed understandings of results.
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post #724 of 1044 Old 11-27-2013, 06:23 PM
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Quote:
Originally Posted by Audionut11 View Post

Ok thanks. So by that determination, this statement below is uninformed (at best)?
I don't know what to say smile.gif. How could he not know how to read a scope output???. So yes, his assumptions that those are peak to peak amplitudes is incorrect. It would be silly to assume that the AVR clipped at just 12 or 13 volts. Unless we are talking about a clock radio amp, the voltages in a consumer amplifier will be far above this. That knowledge alone should have steered Arny away from thinking those were amplifier voltage values.

Unfortunately it also means I uploaded the wrong picture where the scales were not identical. The latest one I post has equal scales.
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And what would you consider to be the dB difference from a 20% voltage difference?
1.6 dB. But as I noted to Arny, this is not the right story on why bi-amping is useful. Music and movie content is not just a smooth sine wave and there are other design factors that make this problem different than it seems.

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post #725 of 1044 Old 11-27-2013, 06:31 PM
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Quote:
Originally Posted by arnyk View Post

Once I complete the test and publish the results I expect to be pecked to death by the usual irrational ducks around here, as happened during the discussion phase. Here are the expected quacks from the ducks:

(1) I'm not doing the test with the duck's quacking speakers.

(2) I'm not doing the test with the duck's quacking amplifiers.

(3) I intentionally fudged the test.

(4) I'm too incompetent to do the test.

(5) I'm not using the quacking duck's music, cables, you name it. I'm not doing it in their listening rooms which don't have the objectivist cooties that infest my workroom.

(6) Mars still hasn't achieved the correct alignment with Venus to properly do a test like this according to the quacking duck astrologers.

(7) My name is not Robert Harley or John Atkinson and their personal magic is required for a test like this to acceptable to the quacking ducks.

LOL!
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post #726 of 1044 Old 11-27-2013, 06:36 PM
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Originally Posted by Audionut11 View Post

I don't know what to say smile.gif. How could he not know how to read a scope output???..

Simple answer - its not a simple oscilloscope.

It appears to be a Agilent 2012 digital oscilloscope which is a very complex multi-function instrument. Given that it claims to have a WXGA screen, it tips its hand and it is actually a signal analysis computer with a high bandwidth ADC-based front end.

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Do more with the power of 5 instruments in 1:
Best-in-class oscilloscope
Integrated logic analyzer (MSO, Optional and upgradable with DSOX2MSO)
Only hardware-based serial-bus protocol analyzer
Only built-in 20-MHz function generator: WaveGen
Only built-in 3-digit voltmeter
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Every one of these instruments has its own screen layout and nomenclature.
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post #727 of 1044 Old 11-27-2013, 06:36 PM
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Originally Posted by amirm View Post

It would be silly to assume that the AVR clipped at just 12 or 13 volts.

It wouldn't be silly from someone like me (I know I'm dumb!). But from someone harping on about knowing all the "relevant" details, simple mistakes like this defy belief.

Quote:
Originally Posted by amirm View Post

Music and movie content is not just a smooth sine wave and there are other design factors that make this problem different than it seems.

Wouldn't the sine wave results translate to some know degree, to the results obtained under a real world load though?
For instance, a 20% increase in Peak to Peak voltage in the tweeter amp with a generated sine wave = ?% increase in available power for the tweeter amp in real world conditions.

If the sine wave responses can't be mapped to real world results, then why would we even consider sine wave results?


Also, I know I have read about the reasons for a sine wave not having flat peaks when the amp is clipping, but for the life of me I cannot recall those reasons. Would you care to expand on that detail?
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post #728 of 1044 Old 11-27-2013, 06:36 PM
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Quote:
Originally Posted by arnyk View Post

The standard electrical engineering term that you are looking for Amir is "Constant voltage power supply". While it may seem to be a nit to the non-engineers reading this thread, it is actually very critical because the two standard extreme cases are constant voltage and constant current and "constant final stage power supplies" is clearly neither or both, IOW nonsense.
You are way confused on this power supply thing Arny smile.gif. Please read my explanation on the Bryston. As I noted there, amplifiers have two or more supply voltages. The first stages are driven by regulated power supplies since they don't have much power demand. The final stage is the main driving element in the power supply and is almost always unregulated. For this reason, you cannot say the power supply is constant current or voltage. There are more than one and you have to be specific about which power supply you are talking about.

Here is the Byrston power supply again:

i-bRBM4C7-M.png
The +-90 volt supplies are unregulated and feed the output stage. The others (30 and 15) are regulated.

So clearly you have to be specific when you talk about amplifier supplies. Just saying "constant voltage" is wrong.
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A trivial observation.
Actually it is not trivial. Time after time you are showing that you can't read a schematic and are not familiar with basics of amplifier design to make such common mistakes.
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Obviously Amir you have zero experience with real world circuits and have no concept of engineering because you are obsessing over nits. Nothing in the real world is exactly constant voltage or constant current. You are trying to make a federal case out of that simple well known fact.
The variable voltage to the output stage can vary by a ton. If for example your incoming house voltage goes from 112 to 118, the 90 volt supply may go up to 95. The regulated 15 volt however may only change to 15.01. That is not a nit at all and is at the heart of why you predicted the two channels having the same output voltage when they don't as I showed.
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Amir how can you say that? The very statement "We don't care about pure sine waves for audibility of amplifier distortion. We care about real music and movie sound. " is nearly a word-for-word quote of what I have posted on AVS almost every day for the past 4 months or more. Here is an example
Actually you have been saying it for the 3 years I have seen your posts here smile.gif. However, what you mean is not at all what I mean when I say the same thing. Understanding what I mean requires true knowledge of amplifier design. That will put in context what happens when you have peaks in real content and what distortion they generate as opposed to a smooth sine wave.

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post #729 of 1044 Old 11-27-2013, 06:40 PM
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Originally Posted by arnyk View Post

Every one of these instruments has its own screen layout and nomenclature.

The result posted happened to show a 10% difference in voltages (for a completely unrelated result, but that which supports your side of the argument) and you jumped all over it without first considering that,
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Originally Posted by arnyk View Post

Every one of these instruments has its own screen layout and nomenclature.

rolleyes.gif
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post #730 of 1044 Old 11-27-2013, 06:43 PM
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Originally Posted by Audionut11 View Post

If the sine wave responses can't be mapped to real world results, then why would we even consider sine wave results?
Let me clarify that some of that can be attributed to what is measured by the sine wave. You can certainly take comfort that the woofer will likely clip faster than the tweeter. So we can bank that advantage smile.gif.

What I will be explaining is that we don't get to say, "oh, it is just 1.6 db so who cares." The actual distortion is more hideous than this number represents due to some not yet talked about components of commercial/consumer amplifiers.
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Also, I know I have read about the reasons for a sine wave not having flat peaks when the amp is clipping, but for the life of me I cannot recall those reasons. Would you care to expand on that detail?
I am trying to set this up like a TV series so that I have something to say tomorrow. biggrin.gif Seriously, I want to make sure we get consensus from everyone that the so called "laws of physics" that mandated the two channels to have identical output is wrong. Arny, Keith, etc., how are we doing on that? Once we are there then I will answer your question.

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post #731 of 1044 Old 11-27-2013, 06:44 PM
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Correct me if I'm wrong, but who cares if it's 0.8db or 1.6dB? Certainly, the more, the better! But what matters is that the tweeter will experience less distortion than the woofer at any given volume. The test proves the tweeter is indeed isolated from the distortion from the woofer, which should be impossible according to the anti-passive-biamping camp. An inconvenient truth?
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post #732 of 1044 Old 11-27-2013, 06:48 PM
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Quote:
Originally Posted by Audionut11 View Post

Quote:
Originally Posted by arnyk View Post

Nothing in the real world is exactly constant voltage or constant current. You are trying to make a federal case out of that simple well known fact. .

Well known! To who?

You mean you don't know?

The fact that nothing in the real world is exactly constant voltage or constant current should be well known to anybody who knows what the phrases constant voltage or constant current mean.

First hit in a google search:

http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Source/Source1.html

"Why worry about an ideal voltage source since nothing like that exists in the real world.?"

This is part of an online EE class.

http://www.facstaff.bucknell.edu/mastascu/elessonshtml/StartEE.html

"Welcome To Exploring Electrical Engineering"

Probably a freshman EE class.

Letsee - the parent folder for this is:

http://www.facstaff.bucknell.edu/mastascu/#Current

Bingo - the class this is from is EE105 - and that would be a first semester freshman electrical engineering class.

Ever attended a university, or must I explain course numbering conventions to you as well? ;-)
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post #733 of 1044 Old 11-27-2013, 06:50 PM
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Originally Posted by amirm View Post

The actual distortion is more hideous than this number represents due to some not yet talked about components of commercial/consumer amplifiers.

Juicy bits still to come smile.gif I look forward to tomorrows episode.

Also, a genuine thanks for sticking to relevant facts and allowing the reader to make their own determinations wink.gif
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post #734 of 1044 Old 11-27-2013, 06:51 PM
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Originally Posted by stereoforsale View Post

Correct me if I'm wrong, but who cares if it's 0.8db or 1.6dB? Certainly, the more, the better! But what matters is that the tweeter will experience less distortion than the woofer at any given volume. The test proves the tweeter is indeed isolated from the distortion from the woofer, which should be impossible according to the anti-passive-biamping camp. An inconvenient truth?

The test proves no such thing since it does not involve even a fraction of a passive crossover based system. It's just something that someone whipped up out of thin air.
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post #735 of 1044 Old 11-27-2013, 06:57 PM
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^^
But according to your theory, this should never have been observed even in such a fraction of a passive crossover based system. Sorry, I'm trying really hard to follow your theory, but it just keeps changing every time you face another inconvenient fact.
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post #736 of 1044 Old 11-27-2013, 07:02 PM
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Originally Posted by stereoforsale View Post

^^
But according to your theory, this should never have been observed even in such a fraction of a passive crossover based system

Not at all. You are making wild extrapolations from what I said.

That is demonstrated by the fact that you can't provide a quote from me to substantiate the above comments.

BTW since you seem to be ignorant of the protocols of online debating, the ability to quote what someone says is used to show that you didn't make your comments up out of whole cloth.

No quotes are tacit admission that you are making it up as you are going along.
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post #737 of 1044 Old 11-27-2013, 07:06 PM
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Originally Posted by arnyk View Post

Not at all. You are making wild extrapolations from what I said.

Or in other words, "if you can't understand my drivel, that's your own problem". Far be it for someone to explain in further detail when a reader lacks comprehension. Labelling other people with the problems is far easier I guess!

We're expected to disregard glaring mistakes in amongst all the drivel, and continue to have blind faith in the theory put forth.
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post #738 of 1044 Old 11-27-2013, 07:27 PM
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Originally Posted by Audionut11 View Post

Quote:
Originally Posted by arnyk View Post

Not at all. You are making wild extrapolations from what I said.

Or in other words, "if you can't understand my drivel, that's your own problem".

Thanks for the insult. It may be drivel to you but I actually spent several hours crafting it. And for what, to be insulted like this?
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Far be it for someone to explain in further detail when a reader lacks comprehension. Labelling other people with the problems is far easier I guess!

My story is that I have been explaining things in further detail for several hours, surfing over copious insults and misunderstandings the whole time.

This particular sequence of posts started with post #718 which went up well over 2 hours ago. Since then I've been online 100% writing posts and researching their background.

I'm writing off the time as stress testing this new 8 core 4 GHz 16 Gb RAM stripe set SSD boot volume Win 8.1 64 bit machine I've been building. ;-)
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We're expected to disregard glaring mistakes in amongst all the drivel, and continue to have blind faith in the theory put forth.

Watching you collapse into insults and spew maybe a little drivel of your own is a bit disappointing but not exactly unexpected. ;-)
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post #739 of 1044 Old 11-27-2013, 07:36 PM
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I would like to think that my opinions are simply a "harsh truth", and my interpretation of your posts. You clearly don't have a problem stating your own interpretations of others intentions and posts!
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post #740 of 1044 Old 11-27-2013, 07:42 PM
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Originally Posted by Audionut11 View Post

I would like to think that my opinions are simply a "harsh truth", and my interpretation of your posts. You clearly don't have a problem stating your own interpretations of others intentions and posts!

If you think about it, stating one's interpretations of others intentions and posts is the polite thing to do. It helps us all figure out where things got derailed when they go off the tracks.

Compare that with insulting comments out of the blue with no supporting quotes...
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post #741 of 1044 Old 11-27-2013, 07:53 PM
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If you think about it, stating one's interpretations of others intentions and posts is the polite thing to do. It helps us all figure out where things got derailed when they go off the tracks.

Actually, pretending to have some idea of the intentions of a person, through no more then written words, is lame at best.

Not to mention, that a persons intent holds no relevance to the conversation. If you can't make a valid argument on the theory alone, then it's probably best to bite your tongue and not degrade the thread into people intents. Intents, that I mention above are borne out of written words solely. Do some research on the interaction between people and you will find that spoken words account for little of the actual communication. There is a significant amount of communication between 2 people that is non-verbal. Obviously, unless your new 3000 core 56ghz computer has some special feature I am unaware of, the internet does not allow the transmission of these non-verbal communications.
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Originally Posted by arnyk View Post

Compare that with insulting comments out of the blue with no supporting quotes...

What's insulting about it?
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Originally Posted by stereoforsale View Post

^^
But according to your theory, this should never have been observed even in such a fraction of a passive crossover based system.

You post one thing that appears to say one thing, and then,

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Originally Posted by stereoforsale View Post

but it just keeps changing every time you face another inconvenient fact.

Seems like a pretty valid observation of your posting style imo.
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post #742 of 1044 Old 11-27-2013, 07:56 PM
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Wow, what a mess.

Amir, I ran some numbers but they didn't make sense. The DSO measurements say "Ampl" and "pk-pk" but the values are similar for the two channels. Those normally differ by a factor of two and do not jive with them having nearly the same vertical scale (V/div). Could you please have the DSO measure the RMS value of each signal? If I treat them both as p-p then the difference based on 85.7 Vpp vs. 79.8 Vpp is 0.6 dB, but the RMS value will be different for a clipped signal. If one is really amplitude and the other p-p then one signal is nearly twice as large as the other, which doesn't seem to fit your stated test conditions of driving them with the same signal? I'm confused.

It would also be interesting to increase the output and see the value when the unloaded (or, lightly-loaded) side begins to clip. That way, we would be comparing voltages at clipping.

Regarding the passive bi-amping debate, Amir's measurements show a larger difference than I have seen before, but then again that was some time ago and on separate power amps that probably had beefier outputs and supplies. Except that the magnitude is a little larger than I would have expected, I am not surprised by this result. At clipping is where any benefit from passive bi-amping would be seen. My problem is, as always, that IMO the real-world benefit is insignificant. You have gained 1 - 2 dB'ish at clipping, not much benefit, and I just do not see most of us (a) clipping regularly if ever and (b) being able to hear the distortion on a real signal when everything is so bloody loud and such large peaks are usually rare and short. I have never disagreed that there are theoretical benefits, but just do not see the benefit in the real world.

Of course, nobody is average, everyone has a system that is constantly pushed to the limits and thus would benefit, hmmm... wink.gif

Clipping is an ugly thing and the actual waveform near and beyond clipping depends upon many factors including power supply capacity and bandwidth, driver and output stage design, load impedance (magnitude and phase over frequency), and so forth. Some early amps would do incredibly nasty things when clipped, up to and including inverting the output. I have not seen anything that bad in ages. I have not seen many pix of clipped amps lately, but glitches and a bit of a slope is common, the latter usually due to thermal effects in the output devices and the rails dropping under the heavy prolonged load.

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post #743 of 1044 Old 11-27-2013, 08:05 PM
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p.s. I took a quick look but am in the same boat as Arny regarding audio preamp and amplifier designs I have done -- decades ago and, while I am pretty sure I actually have the schematics, they are lost in the black hole masquerading as the basement storage room. So as regards audio amplifier circuit theory I have no more credibility than Arny, at least on this forum. Also like Arny, in the real world that is not an issue for me; too many folk have actually seen my work over the years so my professional reputation is not in jeopardy from AVS posters...

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post #744 of 1044 Old 11-27-2013, 08:10 PM
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Originally Posted by arnyk View Post

You mean you don't know?

The fact that nothing in the real world is exactly constant voltage or constant current should be well known to anybody who knows what the phrases constant voltage or constant current mean.

First hit in a google search:http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Source/Source1.html

"Why worry about an ideal voltage source since nothing like that exists in the real world.?"
That was a question in that page. Did you read the answer in the same page? I assume not. Here it is:

"The idea of using ideal sources is something that you may rebel at. After all, there is no such thing as an ideal source anywhere in the world. You can't pull an ideal source off the shelf in the lab, so why are we even talking about them? The answer to that question is that you use ideal sources when you have a non-ideal (a real source) source in a circuit. There are two important things to note.

There are some sources that are very good sources and that can be modelled as ideal sources. (And when that happens, be grateful.) Some situations like that include the following.

A power supply in the lab. Many times you connect a power supply to some electronic circuit, for example, and when you connect the circuit you find that the output voltage from the power supply doesn't change measurably. (After all, power supply designers try to make that happen!) In that case, the power supply might be considered to be an ideal source - at least as long as you are working on that particular circuit."


What I bolded is what I explained with respect to "regulated power supply" (more correct term than ideal voltage source). Fact that they fluctuate a bit is like telling an English teacher how to spell Apple smile.gif. So your coursework agrees with the way I am explaining circuit theory. And there is no "worry" whatsoever.

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post #745 of 1044 Old 11-27-2013, 08:29 PM
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Originally Posted by Audionut11 View Post

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Originally Posted by arnyk View Post

If you think about it, stating one's interpretations of others intentions and posts is the polite thing to do. It helps us all figure out where things got derailed when they go off the tracks.

Actually, pretending to have some idea of the intentions of a person, through no more then written words, is lame at best.

Its possible and even likely for at least some of us. If you can't do it, don't presume that nobody can do it.
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Not to mention, that a persons intent holds no relevance to the conversation.

Obviously, you have insufficient experience with true and genuine trolls. And that is just a start!
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If you can't make a valid argument on the theory alone, then it's probably best to bite your tongue and not degrade the thread into people intents.

So calling my posts drivel was the result of you doing a good job of biting your tongue? LOL!

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Intents, that I mention above are borne out of written words solely. Do some research on the interaction between people and you will find that spoken words account for little of the actual communication.

All true but words are all we have in this context.

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There is a significant amount of communication between 2 people that is non-verbal. Obviously, unless your new 3000 core 56ghz computer has some special feature I am unaware of, the internet does not allow the transmission of these non-verbal communications.

Thank you for destroying your own claims. ;-)
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Originally Posted by arnyk View Post

Compare that with insulting comments out of the blue with no supporting quotes...

What's insulting about it?

What's unclear about your word "drivel"?


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Originally Posted by stereoforsale View Post

^^
But according to your theory, this should never have been observed even in such a fraction of a passive crossover based system.

You post one thing that appears to say one thing, and then,

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Originally Posted by stereoforsale View Post

but it just keeps changing every time you face another inconvenient fact.

Seems like a pretty valid observation of your posting style imo.

I've done the teleconferencing thing for over 30 years. Comments like the above paint a picture of someone who is over their head technically. If you don't understand it well enough, of course it looks like drivel!

I'd give a nickel to slap a blood pressure cuff on you right now. ;-)
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post #746 of 1044 Old 11-27-2013, 09:12 PM
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Originally Posted by stereoforsale View Post

Correct me if I'm wrong, but who cares if it's 0.8db or 1.6dB? Certainly, the more, the better! But what matters is that the tweeter will experience less distortion than the woofer at any given volume. The test proves the tweeter is indeed isolated from the distortion from the woofer, which should be impossible according to the anti-passive-biamping camp. An inconvenient truth?
If there is a difference it is after you pass the knee in the power to distortion curve. Because the flat part of the curve is, um, flat thd is identical throughout that part of the curve. If you never get past the knee in your actual use of your system without boa ping you cannot reduce the very low thd present.

The tweeter amp and the woofer amp get exactly the same signal. In that sense they are not separated. It's like using a y cable to connect the output of say the left channel of a preamp to two separate amp inputs. Same signal in to both amps. Precisely zero difference.

Whether the woofer amp clips sooner than the tweeter amp depends. But if you are at a thd of ten to twenty times the level present at the knee, like say the knee is at .001 percent and you have pushed it up to .02, you are probably below rated amp power since commonly used conservative ratings are watts at 0.1 percent or 0.05 percent. So all that nasty distortion is apparently considered unimportant by everybody from demon to Bryson.

And we are still fussing over levels of distortion that could be reduced to acceptably even more I audible by turning down less than one typically would turn down if things were just a little too loud. Commonly folks adjust by three dB to achieve a meaningful slight decrease in volume.

Really if it makes you feel better do it. But if you have no audible distortion without biamping, reducing the potential distortion that might be present at higher power output accomplishes nothing but psychological comfort.
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post #747 of 1044 Old 11-28-2013, 05:50 AM
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Originally Posted by JHAz View Post

If there is a difference it is after you pass the knee in the power to distortion curve. Because the flat part of the curve is, um, flat thd is identical throughout that part of the curve. If you never get past the knee in your actual use of your system without boa ping you cannot reduce the very low thd present.
A knowledge which we don't have when using our amp. My scope showed that one channel had clipped in a predictable signal, i.e. sine wave. Given that familiarity and an instrument like my scope, we could tell, using *visual* inspection that clipping had occurred. But where are we if I change the sine wave to real music and take away the scope? We would have to use our ears, right? Which gets me to the question I asked: what does clipping sound like? No one has answered that. What if someone compared two amps and heard a difference that is due to clipping in the lower powered amp. Would you believe him if he just said the Bryston sounds better than the amp in his AVR? I assume he would immediately be accused of sighted bias and many posts will be written to convince him that he has not heard anything. So if that is not the right observation and there is no instrumentation, how would one conclude that clipping had occurred?

The question that was asked a couple of times here is quite valid: how much power is enough? As was said, it seems even 30 watts should be good enough. Indeed in these discussions it seems any amount should be as no number is ever given for good enough. Surely this sufficiency amount can't possibly be the case for all listeners, content, speakers and rooms.
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The tweeter amp and the woofer amp get exactly the same signal. In that sense they are not separated. It's like using a y cable to connect the output of say the left channel of a preamp to two separate amp inputs. Same signal in to both amps. Precisely zero difference.
Everyone is clear on this. What some folks are not clear on is that the output stage of the amplifier is load dependent and produces a different results at its peak performance. I explained the theory behind this (unregulated supplies) and showed measurements to demonstrate the same.
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Whether the woofer amp clips sooner than the tweeter amp depends. But if you are at a thd of ten to twenty times the level present at the knee, like say the knee is at .001 percent and you have pushed it up to .02, you are probably below rated amp power since commonly used conservative ratings are watts at 0.1 percent or 0.05 percent. So all that nasty distortion is apparently considered unimportant by everybody from demon to Bryson.
The THD+N curve was computed using test signals not music. The amplifier (a real one as opposed to paper) works differently than these simple measurements show. And further there is no real science behind those thresholds of THD. If two amps clip differently, they will sound differently at that point even if their THD is the same number. Audibility of distortion simply cannot be computed as one number that sums up all the distortion products without regard to what is audible and what is not. Combine this with the fact that the curve we are using to determine THD is not representative of real content and we see why this kind of analysis is not proper for the situation at hand. And that is putting aside that the numbers we pick for THD as in your post have no proof behind them as being representative of any situation in anyone's home.
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And we are still fussing over levels of distortion that could be reduced to acceptably even more I audible by turning down less than one typically would turn down if things were just a little too loud. Commonly folks adjust by three dB to achieve a meaningful slight decrease in volume.
Again, the assumption is that we know clipping has occurred. Someone should explain to me what it sounds like so that we can trust such observations which we normally dismiss without a double blind test of many subjects. This is a bit like redline of an engine. If that is at 5,400 RPM and you stay below 5,000 all is cool. But what if I took away the RPM meter? Can you judge by ear alone that you have hit 5,000? People with a lot of experience may be able to tell. For others, they will hear the engine getting very loud. But perception of loudness is subjective. Are they right in thinking the engine has gotten so loud that it is about to hit redline?
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Really if it makes you feel better do it. But if you have no audible distortion without biamping, reducing the potential distortion that might be present at higher power output accomplishes nothing but psychological comfort.
We are not going to get anywhere until we understand how our systems work. If you knew nothing about engine redline in the above analogy, you would be lost in the woods in attempting to not damage your engine. We think we know what is going on here but so far in an amplifier with real music, that assumption has not proved correct. Lacking detailed knowledge of how real amplifiers work leads us to such dismissive comments. Run your engine anyway you like. You are not going to damage it. If it makes you feel better, stop when it gets pretty loud. But really, you will be doing that for psychological reasons. How does this read to you? smile.gif

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post #748 of 1044 Old 11-28-2013, 07:41 AM
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If there is a difference it is after you pass the knee in the power to distortion curve.
And even then, biamping is only a solution if you are still very close to that knee. Given how little extra headroom it supplies, even granting its advocates' arguments, it will only eliminate the audible distortion if there isn't too much audible distortion to start with. It's the Goldilocks principle of amplification: it only really works if the distortion level is just right.

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post #749 of 1044 Old 11-28-2013, 08:43 AM
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Originally Posted by mcnarus View Post

And even then, biamping is only a solution if you are still very close to that knee. Given how little extra headroom it supplies, even granting its advocates' arguments, it will only eliminate the audible distortion if there isn't too much audible distortion to start with. It's the Goldilocks principle of amplification: it only really works if the distortion level is just right.
How do you know you are or are not "close to that knee?" What if I overshoot way past the knee? What will that sound like? And can your observation of such an effect be trusted since you lack total instrumentation?

Why do you think bi-amp works or doesn't work based on a simple graph using test signals and a composite THD+N number? Is it really this easy to determine the audible effects of distortion?

We are having a technical discussion guys. Please don't keep repeating your argument. We know the argument and I addressed it in my very first post in this thread. So let's not keep repeating the line this late in the game. Present explanation of circuit theory, and understanding of what it means for an amplifier to be pushed to the limit and then we can make forward progress.

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post #750 of 1044 Old 11-28-2013, 08:48 AM
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When connected to a loudspeaker, there is a load to sink power into at all frequencies (even if very small at some frequencies) - it is called a "passive crossover" - ever heard of it? Just because no power is reaching the driver at a particular frequency does NOT mean that the amplifier is not generating power at that frequency. Passive crossovers do not magically create an infinite impedance at all frequencies beyond the band pass. They use passive components - capacitors, inductors, and resistors to block power (yes, through high impedance), reflect power (through charging and returning power to the amplifier) and dissipate power (by converting power to heat).

Now I really am done with this thread.

Before you go, one honest question: what is the impedence for the crossover blocking the unwanted signal? If it's similar to the impedance of the woofer, then this is an extremely important point. I was led to believe the impedence was in fact materially different. ??
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