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In Reply to: If you try this, you'll see what happens... posted by Jacques on August 18, 2006 at 17:10:57:
Not only does the power amp have to contend with the back EMF from the loudspeaker, it has to contend with yet another signal that gets generated independantly from the direct input signal to that amp channel: sound waves from other speakers in the room, which would include the OTHER speaker of a stereo pair, or a subwoofer, or any other active speakers in the room.In order to create these conditions in a test of a power amp, I do not believe it is sufficient to use another power amp as the generator source into the DUT power amp channel. I believe that it would be much more realistic to use an actual loudspeaker system, and have it be exposed to the output from yet another speaker, in order to fully expose the DUT power amp to what it experiences in the real world.
Thus, the DUT power amp channel would be exposed to:
the original input signal,
the back EMF from it,
the acoustic output of the other speaker generating a completely different signal feeding into the output of the DUT power amp channel,
AND
the sound wave vibrations from both speakers!A test bench and a load resistor, or even just another power amp, is NOT going to duplicate this more complete scenario.
Of course, the icing on the cake would be to use some Phi Spectral Multitone test signals for both of the stimuli, using different frequency bands on each of the independant stimuli so as to more clearly see where the distortion is originating from.
Phi Spectral Multitone info can be found in:
AES preprint #4803
"A NEW CLASS OF IN-BAND MULTITONE TEST SIGNALS"with some info at:
http://www.geocities.com/jonrisch/PhiSpectral1.htm
Jon Risch
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Follow Ups:
Not only does the power amp have to contend with the back EMF from the loudspeaker, it has to contend with yet another signal that gets generated independantly from the direct input signal to that amp channel: sound waves from other speakers in the room, which would include the OTHER speaker of a stereo pair, or a subwoofer, or any other active speakers in the room.completely agree, but we must admit that back-emf on one side, and voltage generated by the loudspeaker acting as a moving-coil mike on the other side, have levels way different: the physical mechanism is the same (a moving coil in a static magnetic field), but the later acts upon the whole coil displacement, on several millimeters, the former acts on very weak displacement, in the few micrometers range Note1 .
In order to create these conditions in a test of a power amp, I do not believe it is sufficient to use another power amp as the generator source into the DUT power amp channel.As for me, I do believe.
My rationale is that with this set-up, you can get any di/dt (in the acceptable range) for any dv/dt coming from the PA under test.
With the signal send to the PA under test, and the signal sent the test PA being non-correlated, after a while, all the combinations of di/dt and dv/dt have been exerted.
Put another way, all the reactances range (with energy storage) is scanned.
I believe that it would be much more realistic to use an actual loudspeaker system, and have it be exposed to the output from yet another speaker, in order to fully expose the DUT power amp to what it experiences in the real worldIf you were to assess an amplified speaker, I should completely agree with you.
But a stand-alone PA is to feed an enormous span of possible reactances from thousands of possible brands and types of speaker boxes connected to it.
Doing the test the way you propose would just assess the P.A with your chosen speaker.
By contrast, the test done with a counter-PA scans the possible span of reactances.Thus, the DUT power amp channel would be exposed to:Yes, the PA would be well tested for this speaker . Which is great for an amplified speaker.
the original input signal,
the back EMF from it,
the acoustic output of the other speaker generating a completely different signal feeding into the output of the DUT power amp channel,
AND
the sound wave vibrations from both speakers!
A test bench and a load resistor, or even just another power amp, is NOT going to duplicate this more complete scenario.Here, I disagree. As I wrote above, all the di/dt and dv/dt combinations are exerted this way. So, although it seems odd, the test is more thorough in fact.Of course, the icing on the cake would be to use some Phi Spectral Multitone test signals for both of the stimuli, using different frequency bands on each of the independant stimuli so as to more clearly see where the distortion is originating from.I agree quite completely. Using your set of tones as stimulus for the PA under test would exert it not only in its whole frequency range, but also with a combination of tones, which is better a test than a pure sine.
However, I question using a sophisticated set of tones for the test PA.
What we need for it is to generate the full span of di/dt for the full span of dv/dt from the PA under test.
A single tone does the job in this matter.
So, I do agree you make a thorough measurement by feeding the PA under test with your sophisticated set of mixed tones Note2 , but I don't see what could bring your feeding the test PA with such set of tones.BTW, thanks for the reference. Do some generators use PhiSpectral set of tones preprogrammed? Would be great.
Note1 It would be interesting to calculate analytically those value to assess their ratios.
I'll try to do it this WE or one of those evenings.
However, for similar speakers generating sound and "miking" it, an intuition tells me that it will be somehow less than the squared electric/acoustic energy conversion ratio.
Not even peanuts, but sesam seeds.
Note2 Did you throw an eye on the specifications for ADSL drivers and receivers? Those specs include too a set of mixed tones to assess the IC quality.
The problematics of ADSL, with its hundreds of mixed modulated tones where intermodulation between those has to be assessed below some level, is very similar to the one you explain at the beginning of your paper.
Since money involved in ADSL is thousand times the one involved in high-end audio, you can bet some interesting technological "spin-up" is to mine out from the ADSL guys.
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Your bench test does not include:
AND
the sound wave vibrations from both speakers!The vibration of the power amp is NOT trivial.
If we look at the signal from the loudspeaker very simplistically, then you might think that feeding a signal in from another power amp would suffice to duplicate what goes on with back-EMF, but unfortunately, the timing and phase relationships are not going to be equivalent, the back EMF WILL stress the amp in a manner that a separate indepedant tone (or multiple tones) will not do, because of the current and voltage relatonships of the back-EMF to the orignal signal coming out of the amp.
I understand what you (and many) would like to do: create a more completely cntrolled and replicable test situation. Unfortunately, if we are to arrive at the real truth of what is going on in the real world, we can not ignore certain as[pects because they are inconvenient or untidy.
Yes, use of any particular loadspeaker would technically be valid only for that loudspeaker. On the other hand, a very typical 2-way system could be used as a baseline, and additional test could be conducted on a "typical" electrostatic loudspeaker.
Something approaching the whole truth of the matter, even if it involves a specific loudspeaker system, would be better than ignoring or sweeping under the rug a portion of the truth. Some reaction to a specific loudspeaker would provide more information than not using a loudspeaker.
Your bench test does not include:Because it's another test. I agree that live vibration testing is important, not only to assess the mechanical durability of the equipment (the test procedure of military "Ground-Based"equipement should be used), but also to ensure there is no "microphonics" when vibrating in a static B-field. Test should be conducted on 3 axles. When I see the way some high-end equipent is wired or laid-out on a PCB, with current returns remote from the path their currents come from, there is nothings odd at them being microphonics.
AND
the sound wave vibrations from both speakers!
But again, it's another topic. Many other things to say about vibration tolerance, but it's another topic, that we should cover on another thread.
If we look at the signal from the loudspeaker very simplistically, then you might think that feeding a signal in from another power amp would suffice to duplicate what goes on with back-EMF, but unfortunately, the timing and phase relationships are not going to be equivalent, the back EMF WILL stress the amp in a manner that a separate indepedant tone (or multiple tones) will not do, because of the current and voltage relatonships of the back-EMF to the orignal signal coming out of the amp.This current and voltage relatonships of the back-EMF to the orignal signal coming out of the amp will cover a large span of the possible di/dt and dv/dt for any given V in the acceptable range of the PA.
The proposed test will, after a few seconds, cover all this span of di/dt and dv/dt versus V.
Which is its intended aim.
Which is why I don't understand your objection. It would only be pertinent if some values of both di/dt and dv/dt were not to be generated by the testbench.
Which is not the case as long as the tones used in the DUT amp and the test amp are not correlated
BTW, you could also use a white or pink noise signal to feed the test amp. While it would be good to assess PAs after manufacturing (against some max reference level of the IIM distorsion), it would be less useful for design verification since the casual intermodulation components would just appear like noise.
I understand what you (and many) would like to do: create a more completely cntrolled and replicable test situation.Exactly.
Unfortunately, if we are to arrive at the real truth of what is going on in the real world, we can not ignore certain as[pects because they are inconvenient or untidy.Be careful, you're handling a double-edged axe. Don't hurt yourself ;-))
In fact, I like this test procedure because it exerts the full span of possible situations a PA can get along in its real-world life (I mean regarding only the IIM distorsion or back-emf tolerance, other real world situations like mechanical vibration need other tests)
Yes, use of any particular loadspeaker would technically be valid only for that loudspeaker.OK
On the other hand, a very typical 2-way system could be used as a baseline...Ouch, you just gave yourself a wound with that damned double-edged axe. Feeling fine, I hope?
...and additional test could be conducted on a "typical" electrostatic loudspeaker.Back "esf" (electrostatic force) in electrostatic LPs is unlikely to generate more than a few millivolts... (much more with piezo transducers, but who use them in an high-end environment?).
But to be checked in the lab on real LPs.
That said, the span of di/dt and dv/dt for any V being smaller than with electromangnetic LPs, it will still be covered by the proposed test procedure.
Something approaching the whole truth of the matter, even if it involves a specific loudspeaker system, would be better than ignoring or sweeping under the rug a portion of the truthAgain, be careful with this axe of yours!
"The proposed test will, after a few seconds, cover all this span of di/dt and dv/dt versus V.
Which is its intended aim."This would be true ONLY for a split second at a time when the phase relationships of the test signals happened to coincide in a manner similar to a true back-EMF situation.
The condition would come and go SO FAST, that even if you took a snapshot FFT at the exact moment of a particular coincidence, that the actual portion that coincided would be so small that the effect would be buried relative to all of the rest of the signal present.
However, in the real world, the back-EMF current and voltage phase relationships between the amp output and the speaker would be holding steady for any given tone or combination of tones, rather than occuring only for a split moment and then gone again. If this caused heating of the output stage due to those phase relationships, or activation of the VI limiiter circuits, or caused a bias circuit to drift, etc. NONE of that would show up with the injected tones, the fleeting blip of that special relationship that exists with back-EMF would never be there long enough to be able to be measured readily.
"BTW, you could also use a white or pink noise signal to feed the test amp. While it would be good to assess PAs after manufacturing (against some max reference level of the IIM distorsion), it would be less useful for design verification since the casual intermodulation components would just appear like noise."
Of course, with pink or white noise, it would be impossible to separate out the distortion products from the noise floor, while with a test signal like the Phi Spectral, you could get some information as to where the interactions where coming from, and thus have a chance at determining the mechanism for the distortion.
Your method is pure anarchy. It is the electrical and thermal equivalent of tossing noise and hoping something comes out. And then, when something comes out, guessing and tweaking.Using two controlled signals allows specific conditions to be duplicated, allowing for the capture of transient events. Any condition whatsoever can be duplicated, any thermal history, any location on the VI space, and any vector stimulus on the VI space.
It can measure the response to any condition possible which occurs as a result of any load.
All you state... "heating of the output stage due to those phase relationships...""or activation of the VI limiiter circuits"" ""or caused a bias circuit to drift, etc.""
...can be trivially induced into any amplifier via input drive signals and external drive forcing.
jr: ""
NONE of that would show up with the injected tones, the fleeting blip of that special relationship that exists with back-EMF would never be there long enough to be able to be measured readily.""It is trivial to do such, and in fact, is commonly used even for "refrigerator magnets" here, where measurements during transient conditions are required. Duplication of the transients require huge numbers of passes, and attention to the initial conditions, but that's what engineering is about.
Throwing a huge complex test signal with a terribly difficult to analyze load, is of little diagnostic value other than for tweaking. It may be of some use to spot possible difference before and after, but for understanding of circuit issues, it doesn't provide any insight beyond the guesses one would already have.
Cheers, John
"Your method is pure anarchy."Nope.
"It is the electrical and thermal equivalent of tossing noise and hoping something comes out."
Nope, it is much more than that. One would have to understand things to see it though.
" And then, when something comes out, guessing and tweaking."
Nope. You just have to understand things enough.
"Using two controlled signals allows specific conditions to be duplicated, allowing for the capture of transient events."
Trivially true, it would not capture the effects of back-EMF as stated by Jacques. Transient events could be captured, but the kind of fleeting moment where the VI phase relationships mimick those of a particular frequency with actual speaker induced back-EMF would literally be so fleeting, that they would not represent the actuality of what real back-EMF would do.
"Any condition whatsoever can be duplicated, any thermal history, any location on the VI space, and any vector stimulus on the VI space."
Only if you were to provide an infinitely variable pair of frequencies, and then test for all of the possible combinations, including a set of conditions exactly similar to what occurs with back-EMF. This would obviously be impossible, as one could never cover all the possible frequency combinations, and unless you actually measured the back-EMF, you could never dial in the exact frequency and phase for the second injected frequency, if it were off just a bit, no longer equivalent to back-EMF.
On the other hand, the loudspeaker system does it automatically, continuously, and over a fairly wide range of frequencies. This means that you can run in any decent set of Phi Spectral multitones, and get back-EMF for all the relevant frequencies, pretty much guaranteed.
"...can be trivially induced into any amplifier via input drive signals and external drive forcing."
But only by using an infinitely variable set of test signals, and checking ALL possible combinations, Jacques was talking about one set of specific frequencies as being capable of doing this. No way.
It would help tremendously if you actually knew what you are talking about in this instance. But you don't.
What Jacques said is just not going to work, what you said could be made to work only with infinite test/measurement capabilities, perhaps we should set you to measuring them now, so we can all get some peace and quiet for a LONG time........
;-)
Jon Risch
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jr: ""
It would help tremendously if you actually knew what you are talking about in this instance. But you don't.""This coming from one who had this "phi stuff" rejected for publication, rejected by the test community at large?
I speak of ATE methods which have been used for the last 40 years, and your "method" which nobody in the real community uses, is, better??
If you had the ability to discuss this topic, you would have.. Since you haven't, well, a good man knows his own limitations...
Your a good man.
Your test method was correctly rejected by the AES. It is a noisy, anarchistic approach to a real problem, and it points out nothing, solves nothing. But it has lotsa buzz words.
I laugh at your responses, you avoid technical discussion at all cost.
Your type of "embellishment" is best served at a forum you can control. It is shunned by the engineering community at large, and with good reason.
Tis a shame, as I believe your ability to actually listen and observe is a good one. You raise good questions which need to be asked.
It's too bad the engineering community has only your words to judge you by, as they cannot get past their laughter to see where you do indeed excel..
If you wish to discuss test methodology, do so...stop dissin.
There is no point in attempting to discuss this with you, it is obvious from the beginning that you just don't get it. This is the sad part.From the things you have been posting, it also looks like you have been reading, or in communication with, "Soundmind", who has also shown repeatedly that he just doesn't have a clue about high performance audio issues, nor about certain measurement issues. He certainly does not fully understand the Phi Spectral multitone concept, it's true strength, or what can be gained by it's use. Nor does he understand how the distortion products generated from it are NOT noise, and CAN be fully traced, tracked, and determined as to their origin. In these aspects, you seem to be following eargerly in his footsteps. Ignorance is bliss.
As for my not bending over backwards and upside down and inside out to appease your bizarre requirements for a 'discussion', as in first admitting that you are the ultimate authority on the subject under discussion, sorry, but I can't bend reality that much, and couldn't (nor wouldn't) take enough drugs to do so.
Finally, you are constantly being hypocritical, by stating that you want a nice discussion, but only after you have trashed someone in your post. You jumped in on this thread between Jacques and me, and cast the first stone, and in the same breath, called for a civil discussion.
HYPOCRICY.You don't want a disscussion, you want capitulation, surrender and the last word. It's yours, enjoy your hollow and meaningless victory. This is where science, progress, and truth are really being suppressed and eliminated, by those with double standards and hypocritical behavior.
Jon Risch
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jr: ""
Finally, you are constantly being hypocritical, by stating that you want a nice discussion, but only after you have trashed someone in your post.""You might as well say the sky is green.
I stated your method is the equivalent of electrical anarchy.
You are the one attacking individuals.
Stick to the topic, dude..Look, we all see you are afraid to discuss the topic, so you attack..it's been this way for years.
jr: ""
He certainly does not fully understand the Phi Spectral multitone concept, it's true strength, or what can be gained by it's use""Apparently, he has to stand in line, as nobody else does either.
Submitting a paper is not sufficient. It lives or dies on it's own merit.
So far, yours has not been accepted. Hence, no merit.
JR: ""
This is where science, progress, and truth are really being suppressed and eliminated, by those with double standards and hypocritical behavior.""
That actually defines your behaviour to a tee.
Explain picosecond jitter audibility again?? Or motor-generator?
Your silly concepts cannot withstand peer review.
I've tested amps using active loads since 1982. Pity you don't understand.
Cheers, John
Jneutron, you should watch your input. We don't think much of you either. As far as I can know and tell, you 'help' physicists with their projects. The ONLY technical paper that I have found written exclusively by you had to do with winding coils. You have been added to other papers, but only in a minor way, as someone who contributed, but did not create or control the paper. This is MY external impression, and I could be wrong, but your badmouthing real audio engineers like Jon Risch or me, is absurd! You can attempt to libel us, by bringing up AES politics, etc., but how unprofessional should you get?
Once, Bedini was criticized openly by an electronic engineer who worked at HP. Bedini got his lawyer after HP, and the engineer was severely reprimanded by HP lawyers to not impune the professional credibility of an outside manufacturer while on HP time, using HP resources. Was the HP engineer essentially correct about the Bedini product at the time? I think so, BUT HP didn't think much of being put in a potentially sticky legal position. You should be more careful, or Brookhaven might get to you the same way.
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jc: ""
You should be more careful""Well then discuss the issue. Don't "badmouth me".
Be civil..that is all I ask.
I've no problem discussing the test parts. But, nobody likes being told they don't know what they are talking about.
jc: ""
We don't think much of you either.""You've made that clear from day one.
I, on the other hand, have openly praised the two of you for your contributions.. I have stated openly, many times, that you guys actually LISTEN , whereas most of the engineering world chooses to ignore your observations.
I've stated openly that there are very scientific reasons behind many of your observations.
I've offered to collaborate with you, what did you say....""I wouldn't ask you for the time of day.""
As for JR: Let him speak on his own behalf..if he wishes to discuss, we can..If he wishes to simply badmouth me, so be it. I would prefer discussion, as I believe we all can profit from that.
A "discussion" is not "you don't know what you are talking about". It's about points of contention or agreement. We may not agree, but that is fine..
That is preferred..
Cheers, John
Professional respect is a good thing.
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Jneutron, why are you arguing this point? Jon Risch is the expert here, not you.
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Or, would you like an explanation?Just ask..
Another $25 word or phrase in order to impress the locals?
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JC: ""
Another $25 word or phrase in order to impress the locals? ""Nope. You seem hung up on impressing people. That is not my problem, but yours..
Good thing you asked for an explanation. It is of course, something that YOU as a designer, should be aware of. Guess since you don't know the words, I'll explain..
All power amplifiers operate in four quadrants..two are pure resistive, pos voltage, pos current, neg v and neg I.. quads 1 and 3.
All power amplifiers have to operate in the other two quads, as reactive loads force that. Pos drive, neg current.and versa visa...this is the SOA issue of course.
If you draw the VI space, with voltage as the horizontal axis, and current as the vertical, you see that a resistive load crosses zero, and travels in 1 and 3.
Use of some fancy shmancy test waveform that is entirely uncontrolled, needs the load to push the output into 2 or 4. There is absolutely no control here..IOW, anarchy.
By using two ARB generators, it is trivial to force the out into quad 2 and 4, and it is easy as pie to force the amp from one location on the VI plane, to another. Select the starting point, say quadrant 1 500 watts into 4 ohms, then force the arbs to move the output to another location in VI space. THAT is a vector move, where you have a direction from point 1 to point 2.If you choose to, you can force the positive pass transistors into heavy dissipation in quad 1 via the amps input, then quickly push the amp into quad 2 by the second arb forcing the outputs.
You can preset dissipation, dwell, whatever, and then move (vector) to another position in space. And you can even work the first arb during or after the vector move, to see how long it takes the DUT amp to recover from the vector move. The moves can be any rate desired, they can be sines, whatever..
It tests everything JR alludes to, and it does it fast, repeatable, and accurately. Accuracy being the key.
Obviously, you've never worked with automatic test and data aquisition, have you?.. It can be hairy, I will admit, but with a coupla arbs and a pc, it can produce some excellent tests that would otherwise be impossible. As a designer of amps, I would have thought you knew about this stuff..guess I was wrong..
BTW..by using this setup with rudimentary programming, you can find the line haversine coupling, the ripple coupling, and the pos/neg rail coupling to the feedback divider.. Easy..
Jneutron, you use big words to describe what we real designers already know. Why you would quibble with us over it is my question.
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jc: ""
Jneutron, you use big words to describe what we real designers already know. Why you would quibble with us over it is my question.""
Big words you apparently had no knowledge of.You crack me up.
Explain to us why a test setup that is consistent with anarchy is better than a controlled one?
Hmm? I would enjoy seeing some semblance of technical disscussion out of you.
Clearly, you are unable.
Go go back to your bench and swap resistors out claiming one sounds better than the other, go find a different color wire and tell us why it sounds better, or why one solder sounds better.
Meanwhile, others will apply knowledge to the problem..
You are welcome to ask questions, I'll answer as best I can. But don't think that we believe you understand. That is in your mind.
Give it a break! Jneutron. Vector space: You mean the 2 d graph in 4 quadrants? Please help me with this! VI : This couldn't be Voltage (V) times Currrent (I) could it?
Oh please let it be! That is better than tree sloth brain research or pinpoint locations in visual or acoustic space, which is equally represented by your phrase. Look it up! Now, who is being dorky?
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It would be interesting to engage you in a discussion of damping factor in 5-d space.. You would learn quite a bit, maybe..
jc: ""
Jon Risch is the expert here, not you""Expert in what? Where is he published with respect to amplifier testing?
If you have anything technical to say, then, say it. If not, stay out of the way and let him defend his choices..Stop running interference for him, he's a grown boy now and can speak for himself.
Perhaps you can explain to me why a test regimen which is in use for the last 14 years is suddenly, "unable" to do what it has done. And why one which was not even allowed to see the light of day, is the way to go.
Cheers, John
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