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Old 29th March 2010, 01:29 AM   #1
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Default Completely impressed and saddened by DIYaudio

Have this overwhelming desire to say to so many members how impressed I am with the energy and expense you have gone to in the pursuit of audio. Cheers and accolade to those many of you. It is truly amazing!!

I am equally saddened with a long experience in audio the same errors are being made with the same faulty premises found at the time of my college days in the early 70's. I am so surprised in these 40 years since then little change has occurred, little clarification and almost no corrections of models to the actual physical facts with mathematical simulation now the substitute for laboratory efforts. So now the expert is the guy with a computer instead of a laboratory.

I commend almost all of you and feel sad for you at the same time. Keep on trying though. Am sure some will come upon amazing results which well satisfy their needs like Apexaudio has for his PA work and shared it freely with all. A good thing.

I shall ponder what is learned here for a long long time. Cheers-
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Old 29th March 2010, 01:47 AM   #2
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Originally Posted by sumaudioguy View Post
I am equally saddened with a long experience in audio the same errors are being made with the same faulty premises found at the time of my college days in the early 70's. I am so surprised in these 40 years since then little change has occurred, little clarification and almost no corrections of models to the actual physical facts with mathematical simulation now the substitute for laboratory efforts.
Examples?

CMIIAW, but I figure that ALL lab research is predicated on theoretical models - mathematical or otherwise.

In my own puny way, i follow that line - I set out some design parameters, sketch out a block diagram, work up suitable schematics, model them using the known parameters, adjust for best overall performance, build, test, adjust to fine tune, listen.

Generally , the better my modeling, the less twiddling later.

Since the lab efforts of much more able practitioners are often reduced to mathematical models, I can bypass a lot of the early lab stuff. Surely thats a good thing?

With so many people doing so much in so many different directions in this field alone, let alone associated fields, it seems to me that the reason you have a perception that little has changed is perhaps because there is little to change - that there is nothing new under the sun, and the models that you perceive as somehow lacking actually represent the physical reality with a fidelity that is good enough for even the more critical and educated engineers and listeners.

Otherwise, someone would have done it.
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Old 29th March 2010, 02:59 AM   #3
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Hi sumaudioguy, how could it be any different? I would postulate that the large majority of people posting or reading at diyAudio have no formal training in Electrical engineering. Most would be here because it is a hobby. Many of them will have excellent knowledge gained through research, and experimentation, many of them will be just starting out in this wonderful hobby and have little or no knowledge or experience. There are of course very knowledgeable people with formal training here as well. This can cause friction, especially if their is intolerance of the views of the less informed (a bucket that I will firmly place myself in).

With that in mind, is it not to be expected that many people will make mistakes (and hopefully learn from those mistakes).

As an example take myself:

Over the last few days I have been trying to design a low pass filter using an FDNR. I've been using LTSpice to help me. Everything looked ok (or at least I thought it did) response out to 20K was almost identical to a passive realisation but then deviated (I wasn't too concerned about that as the corner freq was 200Hz). When doing a transient analysis it showed up that the circuit was oscillating at about 80Khz (this is something I would not have been able to detect if I actually had built the circuit as I do not have a scope).

On trying to work out what the problem was (doing a lot of reading) I think that it was the fact that there was a phase reversal after 20Khz that was probably causing the oscillation. I've changed the circuit, the phase reversal is gone, and so has the oscillation. I don't know (or understand) why what I have done has removed the phase reversal, but it worked and I wouldn't have been able to detect (or fix) the problem without the use of a simulator. I now have a much better chance of building a working circuit. Without the simulator, I may never have built the circuit in the first place, as I did not have enough of an understanding of how the circuit worked to be able to progress as far as I have. Iether that or I would have built it, it would have sounded terrible, and I would have given up as I wouldn't have the test equipment to find the problem. Yes I know that even if it simulates ok, it may not work in real life, but the chances are much better.

I will probably post my circuit sometime in the next few weeks (perhaps before, perhaps after I actually have built it). Maybe someone will find it interesting, or possibly even useful. Maybe it will be completely flawed due to my lack of formal training, but I will most certainly not be making any representations as to its fitness for purpose. I may give my own subjective impressions, and probably some objective measurements.

The question is, should I post such a design when I have done so from a starting position of very little theoretical knowledge, no formal training, and just the aid of a simulator to get to where I am? I think that provided I make that clear that there should not be any problem with that.

If I published my design and said it was the best active crossover ever and criticised everyone who begged to differ then I guess that would be a reason to be saddened, but hopefully what I have related above gives an insight into my thinking, and my reasoning as to why a site like diyAudio will always have the potential to have people making the same old mistakes based on the same faulty premises

Tony.
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Old 29th March 2010, 03:22 AM   #4
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When ever I was in college doing research in loudspeaker design in the department of physics the professor and I had decided pretty much everything there was to be know about audio was known by 1940 and forgotten by 1960. This is just a thought though.

I understand the modeling pretty well as an early user and pioneer in perfection of models so I agree the simulations are very helpful but do not at all automatically lead to understanding. Understanding the effects and putting that into a big picture is what I had hoped long ago would happen with time. This clearly has not.

The example of wintermute is great in that he got his circuit working. On the other hand without throughly testing the circuit in the lab that circuit could have unexpected behaviors missed by the simulation.

An example is there is a string right now simulation the Adcom555 amp. It is an oscillator. I have proved it time and time again with many different units with old time storage scopes and "snap shots" of the waveform as the amp breaks into oscillation and then stops while driving a typical cone loudspeaker. That fact is not showing in the simulation.

Another example is the notion a typical speaker is a load. Sorry, wrong. A voice coil loudspeaker is an active source of signal. Any sound is detected by the cone and causes the cone to move thereby driving the amplifier. To model a voice coil loudspeaker simply as a load is naive and always done.

This list could go on and on and on. These are the realizations understanding brings and will never be part of a model until someone puts them into the model.

Another is the common misconception a voice coil loudspeaker has but one resonance. For the moment let me just talk about woofers with resonance in the 10-60Hz range. In reality there is an electrical resonance defined as the current and voltage being exactly in phase with one another as measured at the voice coil. Then there is the mechanical resonance which is defined as the exact peak in the impedance curve as measured at the voice coil. I have never seen these two be the same in testing over 1000 drivers. Sometime these are very far apart but typically the mechanical resonance will be 35Hz and the electrical resonance will be 38Hz. I have seen these different in tweeters by as much as an octave- no kidding! There is no model which includes such behavior. This leads to gross errors in box design of course. Something almost every box designer has experienced who has measured the results as this effect causes gross errors in the Small method.

I can do this all night but believe I have made my point.

When I have talked about these things or written papers and submitted them for publication all that occurs is rejection. It just does not go with the popular idea of the time. Remember please, the earth used to flat and the universe circled the earth and it was heresy to say otherwise punishable by death.
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Last edited by sumaudioguy; 29th March 2010 at 03:29 AM.
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Old 29th March 2010, 03:47 AM   #5
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We have an area on this site for articles - perhaps you could share some of your efforts there? This site has a fairly high concentration of practising Electrical Engineers, many of whom are open to new thinking.
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Old 29th March 2010, 03:52 AM   #6
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Quote:
Originally Posted by sumaudioguy View Post

Sometime these are very far apart but typically the mechanical resonance will be 35Hz and the electrical resonance will be 38Hz.
Well, if thats all it is then Im less worried
I always take for granted that the real Fs is higher than specs
Sure, it could mean phase issues
But I dont see how I can change that

Im more confused about why its to be expected that specs are off

And how often do we say "if only..."
Why is that we know what we want, and the designer often doesnt
Seems like we actually know quite a lot more about speaker design, than the many of those who design the drivers

Nothings perfect, but what can we do about it
We are not in control of the whole world
We can only hope to make the best of the options we have

You want us to understand something
Its not that I dont want to, but I still dont understand what it is you want me/us to do about it

You salute us, thats great
Maybe theres even more going on than you have experienced since january, or there have been
Not every day brings new things to the world
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Old 29th March 2010, 04:04 AM   #7
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Originally Posted by sumaudioguy View Post
When I have talked about these things or written papers and submitted them for publication all that occurs is rejection. It just does not go with the popular idea of the time. Remember please, the earth used to flat and the universe circled the earth and it was heresy to say otherwise punishable by death.
I don't think anyone is going to put you to the sword here.

I DON'T have an EE background, but I'd characterise the issues you have highlighted as being at the finesse end of the spectrum. That is, they do not produce gross errors or even errors that are detectable by the general population. Rather, they are theoretical considerations that MAY have application in very extreme circumstances.

In this your points are not dissimilar to protests over the commonly held descriptions of atomic structure where atoms are described as mini solar systems, electrons regularly orbiting a solid nucleus of protons and neutrons. We have known for quite some time that this is not actually the case, but the simplified concept not only appeals but works at the level that it is being applied.

By and large, that is the realm that we operate in here. In accounting terms, the minute details that you describe fall outside the values that are material to us - the errors they produce are negligible by comparison to the errors produced by other issues (including ourselves!), and in any event, they are not easily controlled.

Cheers!
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Old 29th March 2010, 05:01 AM   #8
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Well, if thats all it is then Im less worried
I always take for granted that the real Fs is higher than specs
Sure, it could mean phase issues
But I dont see how I can change that

Im more confused about why its to be expected that specs are off
In this example the result will throw the popular Theil/Small calculation for Q off by 100% because of the error from the theoretical Theil impedance curve. That wrecks box design. Real Q is say .34 and measure from the impedance curve it is .77. that is no small error and not at the edge or finesse. This also makes the simulations worthless because the data entered are so far off.

I have gone as far a providing manufacturer data and other proofs of what I have learned and truly most of "learned engineers" have blown a fuse. Pretty much all I get is "you do not know what you are talking about." Even with data supporting my claims produced by third parties. Yes some are very interested but the "experts" are dogmatic in both their arrogance and ignorance. This does not help the true DIYer either.

I see this simply as these experts believe that all things audio have been figured out and it is there job to make certain their (very limited) knowledge is correct and held high. To even the casual observer this is not true so... this can only be an ego thing, or lack of self esteem. Some of the non-experts have ask really good questions and even some have made very good observations. To many reject the new knowledge or information which leads to threads of nothing but disagreement where the novice can gain nothing.

Really, I am not into minute detail. Gross errors like oscillating amplifiers and measurement that are off by 100% really muck up the audio design process and worse, the resulting sound defines a new level of awful. Any amplifier that has oscillation while listening is not even an amplifier but an oscillator with amplification. How does that help a DIYer? And it really confuses so many things at every level leading to 40 years of chaos.

On the other hand someone as myself can glean some new perspective especially from some of the real discoverers and some of those fantastic efforts by the guy who has no idea so he is open to anything. To that end I have enjoyed my times here and suppose some others have also.
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Old 29th March 2010, 05:31 AM   #9
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Quote:
Originally Posted by sumaudioguy View Post
In this example the result will throw the popular Theil/Small calculation for Q off by 100% because of the error from the theoretical Theil impedance curve. That wrecks box design. Real Q is say .34 and measure from the impedance curve it is .77. that is no small error and not at the edge or finesse. This also makes the simulations worthless because the data entered are so far off.
I for one would like to learn more about that and how to separate the 2 resonances out...

dave
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Old 29th March 2010, 10:59 AM   #10
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I second that Dave.

You have my (and others) ears pricked, are you going to give up now? You seem to have more self esteem than that.

I'm far too much a noob to argue, I strive to be enlightened.
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