ingrast said:
Fwiw, this is an example that I have typically cited for decades now... while I don't know if it is original with me, and I doubt that it is, but I think it's the single best way to explain why "stereo" is actually only has a single dimension: left<--->right!
All of the "other" perceived dimensional and spatial effects are synthesized in the brain as the result of mostly amplitudinal cues that are learned out in the real world, and even there are created out of "whole cloth" in the brain. The idea here being that the brain tries to make "sense" out of the sonic cues. It then "fits" the raw sound into a context (in large measure learned, as it is...) that makes sense to the individual listener.
Imho, this process is critical to understanding both the mechanisms in listening to audio, and to the processes in reproducting audio/music...
Full circle, the less time it takes for the brain to grasp the nature of the cues being presented, the "more natural" the reproduction appears, and the more time the brain has to then work on the subtle cues.
Which in practice is why a table radio or low bitrate mp3 still sounds like music, and why merely detecting some of the things that are frequently debated and written about, their very existence being questioned, is not so simple to do or easy to pass judgement upon.
<steps down from podium>
_-_-bear
PS. I'm pretty sure I could have supplied the Blow Torch enclosure at a better price... Bob was not receptive at the time...
mikelm said:
mikelm,
What you might want to investigate is the sound of (the same) speakers in a typical living room, vs. a relatively large room!
BIG difference!
The reverb time is what does it.
A room that is way too live (too much reflection/reverberation) in construction in a typical sized room, is heavenly in a relatively large room!!
The size I am speaking of is say 30ft wide and 60 ft long? Ceiling to match in proportion.
Of course intermediate sizes going down to "normal" room size, represents a continuous variation of effect.
The ear/mind connection prefers larger spaces it seems.
Ergo, "concert hall" sound...
Imho, of course.
_-_-bear
Bob Cordell said:
Just a little point or two; A high power amplifier design of several hundred watts using lots of output pairs will have an intrinsically low output impedance, even before the application of global NFB, and especially so if high fT BJT's are used.
It is exceedingly silly to base an argument on both the general need and “audibility” of output coils on such a design.
A low power design with only a few output pairs, if not just a single pair, will have an output stage with a much higher intrinsic output impedance – especially so if a MOSFET output stage is used in favour of a BJT output stage, which may have a higher output impedance due to the lower transconductance of MOSFET devices over BJT’s.
A low power MOSFET power amp with low global negative feedback enclosing the output stage can have a reasonably large equivalent output inductance.
Cheers,
Glen
How about this, Bob? Post #796
"... Your mention of Otala is relevant here. I think he could be considered an unconventional thinker. Indeed he was one of the smarter and well-informed unconventional thinkers. Unfortunately, he had some blind spots. While much of what he asserted was technically correct in some respects, he reached bottom-line conclusions that were simply wrong and have long since been disproved. ???????
... He went on to wrongly conclude that large amounts of negative feedack were the cause of TIM, and that the solution was low feedback or no feedback. (Works for me!) In so doing, he misled an entire generation of audio engineers. He also proposed other forms of distortion that were supposedly caused or exacerbated by NFB, such as PIM and IIM, and was again proven wrong when others carefully examined his results. ..."
AND ON AND ON IT GOES! This is really low rent, especially since Otala is not available to defend himself, as he has suffered strokes that limit his participation, if he is even alive at this time. I have known and worked with Matti Otala for years. I KNOW what he thinks and when his ideas work or not.
Cordell is just trying to make himself look good by trashing Otala.
27 years ago, we completely trashed Bob Cordell with an approximately 25 page rebuttal that was sent to him. It was signed by Matti Otala Dr. Marshal Leach, Walt Jung and me. Just wait till I dig it up!
"... Your mention of Otala is relevant here. I think he could be considered an unconventional thinker. Indeed he was one of the smarter and well-informed unconventional thinkers. Unfortunately, he had some blind spots. While much of what he asserted was technically correct in some respects, he reached bottom-line conclusions that were simply wrong and have long since been disproved. ???????
... He went on to wrongly conclude that large amounts of negative feedack were the cause of TIM, and that the solution was low feedback or no feedback. (Works for me!) In so doing, he misled an entire generation of audio engineers. He also proposed other forms of distortion that were supposedly caused or exacerbated by NFB, such as PIM and IIM, and was again proven wrong when others carefully examined his results. ..."
AND ON AND ON IT GOES! This is really low rent, especially since Otala is not available to defend himself, as he has suffered strokes that limit his participation, if he is even alive at this time. I have known and worked with Matti Otala for years. I KNOW what he thinks and when his ideas work or not.
Cordell is just trying to make himself look good by trashing Otala.
27 years ago, we completely trashed Bob Cordell with an approximately 25 page rebuttal that was sent to him. It was signed by Matti Otala Dr. Marshal Leach, Walt Jung and me. Just wait till I dig it up!
John, I was taught by Marshall Leach in the mid '70s. He gave up on Otala's "wide open-loop bandwidth" concept around '77 or so. He told us why way back then. And the history of the schematics of his amp demonstrate that clearly also. Just look at the schematic from his original article in "Audio" and compare it to the latest one on his site.
Oh, I'm dead serious! But I don't want you to think that I am mad or anything like that. It gets tiresome over the decades to go through this time and again. Matti Otala was NOT 100% correct on everything, but he was THE pioneer, not Bob, or even me. My forte is circuit topologies, and that is what I contributed in the early days.
myhrrhleine said:
Have you ever done this sweep in your room? I did. You will be in for a shock. All those reflections will cause a large number of frequency irregularities, from build-up to cancellation. The effect will be less with highly beaming speakers, and if you can afford to use an abondoned church as your listening room it will also be less, but normally we don't want that because we need some reflections for 'life' in the music. Then, as said, music itself causes constuctive and destructive interferences.
I don't disagree with you that the effect existst. I don't disagree with you that we strive to eliminate errors as much as possible. I just think that adjusting the acoustic centers of your drivers doesn't do so much for the end result. I wouldn't spend too much money on it. But, of course, YMMV.
Jan Didden
Re: Re: Re: Re: Re: Re: definition of 'rock solid'
Hi Glen,
Yes, you (and me) are referring to it. We are still talking about the definition of "rock solid", see post subject. In other words accuracy. What else are we talking about here?
Let us recall why we started this discussion anyway. Because of Graham's remark that the input filter is "part of the NFB sensing loop". Then, I have shown that a typical input filters can make a difference of 5 degrees (slightly more than 0.01), and, imho, a "rock solid" method should reveal this.
BTW, a cap across Rf isn't my choice either; it was is only meant as an example to illustrate the different outcomes between the two method's.
Anyhow, I don't have any objections to calling your method "rock solid" as long as you refer to the open loop gain and not to the NFB loop gain.
Cheers, Edmond.
G.Kleinschmidt said:
Hi Glen,
Yes, you (and me) are referring to it. We are still talking about the definition of "rock solid", see post subject. In other words accuracy. What else are we talking about here?
Let us recall why we started this discussion anyway. Because of Graham's remark that the input filter is "part of the NFB sensing loop". Then, I have shown that a typical input filters can make a difference of 5 degrees (slightly more than 0.01), and, imho, a "rock solid" method should reveal this.
BTW, a cap across Rf isn't my choice either; it was is only meant as an example to illustrate the different outcomes between the two method's.
Anyhow, I don't have any objections to calling your method "rock solid" as long as you refer to the open loop gain and not to the NFB loop gain.
Cheers, Edmond.
john curl said:
Yeah!
Look!
Process of education consists mainly of "partial truths", that can be called even "lies" after years and there is nothing wrong in it. For example maths in primary school, no teacher tells the children about roots of negative numbers, did the techer mislead? NO!
Same goes to science! We do not blame scientists thoughout centuries just because we know better now.
Re: Re: Re: Re: Re: Re: Re: definition of 'rock solid'
Edmond, my “negligibly small” remark was with regards to the phase and gain difference between the non inverting and inverting inputs.
Well, didn’t I actually say that the method was simply my way of measuring the open loop gain and phase response of the amplifier?
The phase shift incurred by the input filter is pretty much irrelevant as far as the global negative feedback loop is concerned, and as I mentioned before, the phase shift of the input filter can be disregarded for the test I outlined simply by connecting the cro probe for the reference trace after the filter. Anyway, if we want to measure the phase shift of the input filter, we hardly need to conduct an open-loop analysis.
Cheers,
Glen
estuart said:
Edmond, my “negligibly small” remark was with regards to the phase and gain difference between the non inverting and inverting inputs.
estuart said:
Well, didn’t I actually say that the method was simply my way of measuring the open loop gain and phase response of the amplifier?
The phase shift incurred by the input filter is pretty much irrelevant as far as the global negative feedback loop is concerned, and as I mentioned before, the phase shift of the input filter can be disregarded for the test I outlined simply by connecting the cro probe for the reference trace after the filter. Anyway, if we want to measure the phase shift of the input filter, we hardly need to conduct an open-loop analysis.
Cheers,
Glen
Re: Re: Re: Re: Re: Re: Re: Re: definition of 'rock solid'
Hi Glen,
Maybe you didn't, but in any case, applying the test signal to the positive input, implies measuring the open loop gain and phase response .
As long as you mean the phase shift from the input to the base of Q1, i.e. the phase shift of the filter in its own right, you are perfectly right. But that's not what I mean. I'm talking about the influence of the components of such filter on the NFB loop, and that's quite a different thing. To be more specific, a relative high impedance (R1=2k & C2=0), shown by the base of Q1, will cause an additional phase shift, 5 degrees for example, as illustrated in my previous post #801. Your method (looking at the phase shift from Q1 to output) will not reveal this and therefore is not always rock solid.
Sure! At least one thing we can agree on
Cheers, Edmond.
G.Kleinschmidt said:
Hi Glen,
Maybe you didn't, but in any case, applying the test signal to the positive input, implies measuring the open loop gain and phase response .
G.Kleinschmidt said:
As long as you mean the phase shift from the input to the base of Q1, i.e. the phase shift of the filter in its own right, you are perfectly right. But that's not what I mean. I'm talking about the influence of the components of such filter on the NFB loop, and that's quite a different thing. To be more specific, a relative high impedance (R1=2k & C2=0), shown by the base of Q1, will cause an additional phase shift, 5 degrees for example, as illustrated in my previous post #801. Your method (looking at the phase shift from Q1 to output) will not reveal this and therefore is not always rock solid.
G.Kleinschmidt said:
Sure! At least one thing we can agree on
Cheers, Edmond.
john curl said:
Hi John,
In your post #807 on this thread you said:
"Jan, Bob calls people who are NOT on this board, fools, etc. "
I then asked what you were referring to, since I have never said that people who are not on this board are fools or anything else.
How does the above rant by you constitute an answer to that question? This is unfortunately typical for you. You make a denigrating statement about a person or a technology, and then when asked to back it up you either don't answer or you answer with some baloney that is minimally relevant that doesn't answer the question.
This is why people pound on you here.
Bob
I don't think that it is that extreme as long as the drivers in question cover different frequency ranges. The lower driver would produce much less SPL at the higher frequencies and therefore have less "notching ability".
Enclosed you will find the simulation of a subtractive crossover @ 1 kHz effective crossover frequency (2nd order highpass 1st order lowpass). Blue is the highpass output and yellow is the derived lowpass output. The green trace is the sum with the higpass leading by 300 us and the red trace is the sum with the lowpass leading by 300 us. Keep in mind that 300 us is quite a lot in this frequency range (about 10 cm offset). One can clearly see the decreasing response aberrations if one is moving away from the crossover frequency.
Sorry for the OT.
Regards
Charles
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