This is a very interesting point indeed. In 3 waveguides I tested, all seemed to amplify the 20KHz breakup mode which also drops when moving off axis. The sound is different when the ear is exactly on-axis. But since the impulse is also different, I would expect such difference in sound.Elias said:
Elias said:
Elias,
Take a little bit of your own medicine and read the very fist line below the heading which states that the paper is an advanced manuscript that has not been reviewed by the board!!!
Thanks for contradicting yourself twice with your own links.
Hello,
Makarski analyses HOM generated by the driver and shows radiation patterns for several higher order modes in a couple of different horns. Can we trust these papers? Are the polar plots correct?
I don't understand what does it mean 'you didn't pursue it further'. You got different results or what? Do you have measurents to show polar plots of higher order modes (any horn will do) for comparison?
By the way, is there any reason to suspect the validity of Makarski's results (the polar plots)?
- Elias
Makarski analyses HOM generated by the driver and shows radiation patterns for several higher order modes in a couple of different horns. Can we trust these papers? Are the polar plots correct?
I don't understand what does it mean 'you didn't pursue it further'. You got different results or what? Do you have measurents to show polar plots of higher order modes (any horn will do) for comparison?
By the way, is there any reason to suspect the validity of Makarski's results (the polar plots)?
- Elias
gedlee said:
Elias said:
I see the tactic, attack first and ask questions later. Seems to be a fairly common trend as of late.
Hello,
"data" hmm.. well, anyway.
This result is very different from Makarski. You say horn is important contribution factor whereas Makarski says horn does not have an influense. Nothing wrong to have different results! However one must wonder what is the cause of this difference.
Makarski says in the paper he analysed 50 combinations of different drivers and horns. He measured the velocity distributions using his method and found the result is nearly independent on the horn used (indirect quote).
To me 'nearly independent' has a meaning 'not beeing important or dominating factor' in this case.
Do you think Makarski have made errors in this case so we cannot trust his papers?
- Elias
gedlee said:
"data" hmm.. well, anyway.
This result is very different from Makarski. You say horn is important contribution factor whereas Makarski says horn does not have an influense. Nothing wrong to have different results! However one must wonder what is the cause of this difference.
Makarski says in the paper he analysed 50 combinations of different drivers and horns. He measured the velocity distributions using his method and found the result is nearly independent on the horn used (indirect quote).
To me 'nearly independent' has a meaning 'not beeing important or dominating factor' in this case.
Do you think Makarski have made errors in this case so we cannot trust his papers?
- Elias
Hmm.. Still thinking about Makarski's results. Could it be possible he didn't find any influence of the horn in his results be due to the level of the HOM generated by the horn was number of magnitude lower than the HOM generated by the driver? Otherwise it would have been shown in the results as he did a combination of analysis of different horns and drivers. Or could it be that all the horns he used produced equally amout of HOM so it could not be distinguished from the driver HOM?
Anyway, to measure the HOM of a horn, one needs to have a driver which does not produce any HOM. Is there such a driver existing? If a driver generates HOM how do we know which HOM comes from the driver and which from the horn?
- Elias
Anyway, to measure the HOM of a horn, one needs to have a driver which does not produce any HOM. Is there such a driver existing? If a driver generates HOM how do we know which HOM comes from the driver and which from the horn?
- Elias
Elias said:
Elias
I will not continue to comment on rude comments so either change your tone or expect to be ignored.
I answered this question previously:
"This is the one part of the Makarski paper with which I take exception. I was a reviewer of the paper for the AES and I raised this issue and asked for proof of it (this was a peer reviewed journal where statements DO have to be proven or referenced). When one was not forthcoming the paper was rejected for publication which is why it is only available as a preprint (preprints are NOT reviewed)."
Markarski was not looking for the effects of the waveguide on the HOM of the diaphragm. He wanted to know how the breakup modes of the diaphragm would affect the polar response and in this context his work is very good. But this IS NOT what we are talking about here. His statement about the horn not contributing to the "acoustic HOM" was wrong, plain and simple and the reason that the paper was never published in the JAES. The rest of the paper is correct, but note one very important aspect. He said that the HOM did not have a major effect on the energy distribution in the radiated field and this is true. What he DID NOT DO or state was if the HOM, even though they are low in level, were audible or not. Remember that THD has almost no effect on the energy distribution but can be quite audible. Eneregy level and audibility are quite different things. In the context of the discussion here, Makarski's paper can only be used for proof that HOM do exist because he measured them, but you really cannot use it beyond that since he was not looking at or for acoustic HOM or the audibility of the same. I beleive that I am the only one to have done work in that context.
Earl,
This is getting ridiculous. The problem in you is you assume everyone is attacking you personally. A true scientist would know how to differentiate personal issues from professional ones. I have no personal interest on you, or any other authors here or anywhere whatsoever.
And about my question "Do you think Makarski have made errors in this case so we cannot trust his papers?"
You said you were a reviewer of his papers, and because the paper apparently did not get published in the journal I'm finding out the reason if there were some errors in it. A perfectly valid question I proposed. But no, you think I'm beeing rude..
- Elias
THIS I find very rude:
This is getting ridiculous. The problem in you is you assume everyone is attacking you personally. A true scientist would know how to differentiate personal issues from professional ones. I have no personal interest on you, or any other authors here or anywhere whatsoever.
And about my question "Do you think Makarski have made errors in this case so we cannot trust his papers?"
You said you were a reviewer of his papers, and because the paper apparently did not get published in the journal I'm finding out the reason if there were some errors in it. A perfectly valid question I proposed. But no, you think I'm beeing rude..
- Elias
THIS I find very rude:
gedlee said:
Elias
Perhaps I was a little rash with you and for that I appologize, but I am getting tired of being attacked whenever I post how HOM function. Most people have it wrong.
The single biggest mistake being made in all these posts on HOM is to over simplify what is a very complex issue. Not uncommon in situations like this. There are people on other threads who talk as if they understand them and yet appear to have it wrong according to my understanding.
I always respond to polite questions, but seldom to attacks on my competance or integrity.
To your questions. Yes, the driver could swamp out the HOM in a waveguide if it were designed with low HOM contribution. The opposite could also occur. Makarski was not looking precisely for what we are talking about here so it should come as no surprise that he did not find it. His interest was diaphragm breakup modes and how they couple to the horn. He quite correctly found that the horn had little to no effect on these modes. But he did not consider the HOM created acoustically in the waveguide itself, it was simply not his interest. He did show that the wavefronts in a horn were anything but single mode, that HOM did exist, the point here being that any discussion of they actually being HOM is pointless because it has been proven that there are.
The point open to discussion is how audible they are. Makarski's paper has nothing of relavence in this context.
Perhaps I was a little rash with you and for that I appologize, but I am getting tired of being attacked whenever I post how HOM function. Most people have it wrong.
The single biggest mistake being made in all these posts on HOM is to over simplify what is a very complex issue. Not uncommon in situations like this. There are people on other threads who talk as if they understand them and yet appear to have it wrong according to my understanding.
I always respond to polite questions, but seldom to attacks on my competance or integrity.
To your questions. Yes, the driver could swamp out the HOM in a waveguide if it were designed with low HOM contribution. The opposite could also occur. Makarski was not looking precisely for what we are talking about here so it should come as no surprise that he did not find it. His interest was diaphragm breakup modes and how they couple to the horn. He quite correctly found that the horn had little to no effect on these modes. But he did not consider the HOM created acoustically in the waveguide itself, it was simply not his interest. He did show that the wavefronts in a horn were anything but single mode, that HOM did exist, the point here being that any discussion of they actually being HOM is pointless because it has been proven that there are.
The point open to discussion is how audible they are. Makarski's paper has nothing of relavence in this context.
gedlee said:
This is the answer I was looking for. So Makarski made an error in his statement.
However, I still wonder why he did not see any evidence of horn HOM in his measurements? Ignoration or measurement error or what?
One remarkable thing he did is he quantisised the amount of HOM generated by the driver. I never see anyone do the same for a horn.
Maybe he was not looking for horn HOM as a starting point, but if it would be present in a great amount in his measurements, why he did not see it. That I don't understand.
Is horn HOM so very different in appearance of driver HOM it cannot be recognised in a measurement without prior knowledge of it? Afterall, as I understand, what he measured was spatial velocity and pressure distributions at the soundfield after the horn. Any HOM should be visible on that, or not?
- Elias
Elias
Its been awhile since I read the paper, but here is the issue.
If I measure the wavefront at the mouth of a horn, then I know exactly how it will radiate. Now this wavefront will be the sum over all the modes in a plane aperature, Bessel functions if it is a plane. But these modes are NOT the modes of the waveguide as those are Spherical Harmonics. There is a relationshp between the Spherical Harmonics and the Bessel functions and one could then calculate the wavefront in terms of the Spherical Harmonics. The lowest order mode is that of a uniform velocity profile on a spherical surface. This is the "main mode" of wave propagation in a conical waveguide - all waveguides become conical at the mouth. Now if, and this will almost always be true, there is deviation from a perfectly uniform wavefront on the hypothetical spherical surface in the mouth, then this deviation has to be the result of HOM. It would be an almost insurmountable task to derive how much of the HOM at the mouth was due to the three possible sources of HOM creation 1) the driver diaphragm modes 2) the phase plug and interface, 3) the waveguide itself.
In all cases, regardless of the cause, the HOM are dispersive and arrive later than the main mode.
When I was working with B&C we did some measurements of the HOM content from the drivers themselves and it was not zero. It was in fact very complex.
In my work, the driver and its phase plug are a given, nothing that I can do about those (although there is a lot that could be done). So my premise has always been to reduce the HOM in the waveguide and accept those in the driver. The foam was an attempt to reduce the HOM that I could not control in the waveguide itself through its design. The bottom line is that this all worked. Can I sort out precisely what is due to what? No thats immensely complicated and unnecessary. The bottom line is that the problem is gone - it would be nice to know the details of this fix, but its not necessary. I choose to just move on and accept the solution at face value. I don't have the time to delve into the details of precisely why it works . The hypotheis is clear from the results. The driver contributes to the HOM content but can apparently be corrected with the foam, the waveguide also contributes since a better waveguide yields a better sound quality. I also believe that there are other factors involved having to do with Acoustic Entropy - but thats a whole other topic.
Its been awhile since I read the paper, but here is the issue.
If I measure the wavefront at the mouth of a horn, then I know exactly how it will radiate. Now this wavefront will be the sum over all the modes in a plane aperature, Bessel functions if it is a plane. But these modes are NOT the modes of the waveguide as those are Spherical Harmonics. There is a relationshp between the Spherical Harmonics and the Bessel functions and one could then calculate the wavefront in terms of the Spherical Harmonics. The lowest order mode is that of a uniform velocity profile on a spherical surface. This is the "main mode" of wave propagation in a conical waveguide - all waveguides become conical at the mouth. Now if, and this will almost always be true, there is deviation from a perfectly uniform wavefront on the hypothetical spherical surface in the mouth, then this deviation has to be the result of HOM. It would be an almost insurmountable task to derive how much of the HOM at the mouth was due to the three possible sources of HOM creation 1) the driver diaphragm modes 2) the phase plug and interface, 3) the waveguide itself.
In all cases, regardless of the cause, the HOM are dispersive and arrive later than the main mode.
When I was working with B&C we did some measurements of the HOM content from the drivers themselves and it was not zero. It was in fact very complex.
In my work, the driver and its phase plug are a given, nothing that I can do about those (although there is a lot that could be done). So my premise has always been to reduce the HOM in the waveguide and accept those in the driver. The foam was an attempt to reduce the HOM that I could not control in the waveguide itself through its design. The bottom line is that this all worked. Can I sort out precisely what is due to what? No thats immensely complicated and unnecessary. The bottom line is that the problem is gone - it would be nice to know the details of this fix, but its not necessary. I choose to just move on and accept the solution at face value. I don't have the time to delve into the details of precisely why it works . The hypotheis is clear from the results. The driver contributes to the HOM content but can apparently be corrected with the foam, the waveguide also contributes since a better waveguide yields a better sound quality. I also believe that there are other factors involved having to do with Acoustic Entropy - but thats a whole other topic.
gedlee said:
depends if you measure the vector and time of arrival as well – this would sort out interference form the main wave front – still - I don't see any point in discussing mere interference (HOM) as to be exceptionally interesting – you nowhere responded to that "non interaction agreement" of interfering wave fronts when I brought that up.
By its own this interference (HOM) doesn't do anything you claim (sound wise) IMO – unless we bring some specific interaction into play as already mentioned.
Michael
mige0 said:
Michael
I want to be as polite as possible, but I do need to say that you have the HOM thing completely wrong. By your own admition the math is over your head and if thats the case then there simply is no way to argue with you since any proof of my claims would likewise be over your head. IMO you are far too quick to jump to conclusions over a few simple tests and your "opinion" about how acoustics works. I just want you to understand that I do not agree with much that you have said regarding HOM. Mostly what you are saying doesn't make much sense to me, but its clear that you don't accept HOM as something significant. Thats fine, your entitled to your opinion, just so long as you understand that I don't agree with it.
gedlee said:
Polite, but still "bad form".
The only thing you have done here is antagonize readers, not just the respondent.
It basically reads like: your wrong, your stupid, you can't possibly understand. (..though again, a polite version of that.)
THIS is what incites someone like Doug20 to make attacking comments. And obviously it's also what incites someone like me to provide a post like this.
The solution? (..all suggestions that I attempt, though I am not always successful with.):
Pick those areas you are able to correct, and try to do so politely. Be ever vigilant to abstain from *ever* directly stating that someone is incorrect (no matter how incorrect they might be), yet always be forthcoming when someone is correct, or even partially correct.
Alternatively, (if unable or unwilling to to accomplish the above), try not to respond no matter how much you feel compelled to.
And once again, please do not make demands of others - always try to form a potential demand as a *polite* request.
(Btw, with the exception of this "slip" and the earlier starter "slip" with Elias, I think your post have improved (especially considering the whole HOM measurement thread) - you even "handled" my posts well, and yes I was fully aware of it.) 😀
Scott
Thanks for the comments.
I have remained out of the discussion on HOM over at the other thread because it is just going round and round on the same old misconceptions that I tried to correct early on, but no one appeared to be listening, so I abandoned that thread. Now Michael has followed me here with a post obviously meant to ellicite my response to the same things that he stated over there. I am not interested in getting into an argument over how HOM work - I know how they work.
I never said that Michael was "stupid" or that "he couldn't possibly understand" but if he is not going to try and understand then I am not going to try and explain it to him.
"all suggestions that I attempt, though I am not always successful with.):"
That comment I can certainly agree with.
Thanks for the comments.
I have remained out of the discussion on HOM over at the other thread because it is just going round and round on the same old misconceptions that I tried to correct early on, but no one appeared to be listening, so I abandoned that thread. Now Michael has followed me here with a post obviously meant to ellicite my response to the same things that he stated over there. I am not interested in getting into an argument over how HOM work - I know how they work.
I never said that Michael was "stupid" or that "he couldn't possibly understand" but if he is not going to try and understand then I am not going to try and explain it to him.
"all suggestions that I attempt, though I am not always successful with.):"
That comment I can certainly agree with.
Unsubstantiated negative opinion deleted.Come on guys, I'm all for a good discussion but you have to back your position up with facts. Let's keep an eye on the goal and progress the science.
How does anyone really expect Geddes to stay out of these threads and just let the tide roll however it may? There are and have been multiple threads clearly aimed directly at things which Geddes himself has spent his career in researching. All these threads are asking for poaching information to find ways to get the same results for less. When people are not understanding the full scale of the problem or are completely wrong you expect the original source to just be quiet while he is 'seemingly' contradicted. Every thread here turns into an attack on the actual intelligence that Geddes has been more forthcoming than anyone I have seen other than Nelson Pass.
If I were Dr. Geddes I would stand my ground and correct people who think they have found all the answers in a matter of hours.
If I were Dr. Geddes I would stand my ground and correct people who think they have found all the answers in a matter of hours.
ScottG said:
Scott,
Be fair.
Yes, Dr. Geddes is often blunt. And yes he could soften the impact by saying, "that analysis is wrong", instead of "you are wrong". No, he ain't perfect.
But c'mon. If you want to paraphrase do it both ways. Michael has said, what sounds to me like; "HOM is nothing more than common interference, i.e., your assertions regarding HOM as an distinct form of distortion are just your imagination".
Let's compare the two. Michael is an intelligent DIYer, with experience building speakers and who has modeling skills. Dr. Geddes is a professional in acoustics, with an advanced degree and a record of peer reviewed publications. And he has spent a lifetime of work on these kind of issues. And built speakers. And has developed and written programs like Michael buys and uses. Doesn't mean he can never be wrong. And sure, Michael is entitled to express his opinion. And I like to read what he has to say. He may not have intended the meaning that I perceived. But if we are going to grade tone, Michael's (and other's) apparently dismissive tone is the far greater insult.
If I have to choose who the greater asset is to my understanding of these issues, I know where my money is, and it isn't close. Every one is entitled to chime in on these issues. But that doesn't mean that all opinions have the same value. If you want to learn from the man, cut him some slack and accord him a modicum of professional respect.
Sheldon
BTW, Dr. Geddes and John K. often lock horns on technical issues, and go toe to toe, but I never see it get personal or petty.
gedlee said:
I can live with that being seen as a pretty thumb person 😉 thanks for being polite – I appreciate that !
But to be serious - still you haven't answered the core question as you avoid usually :
Does the law of "non interaction agreement" of interfering wave fronts apply for you?
Michael