Jmmlc said:
Being interested and doing testing myself in diffraction outside of horns/waveguides, it is obvious that this is the beneficial aspect. Were this not the case, the foam would be completely ineffective. I don't see the point of the comment. One desires to filter out the HOM, i.e., reduce their level in relation to the main wave. They cannot be separated in a specific measurement, but it seems obvious to me at least that they can be treated separately in that they can be reduced to greater degree than the main wave by the simple fact that they do not move in the same path as the main wave, being diffraction effects. The simple fact that they pass through a longer path means that they are filtered differently, more highly damped, than the main wave.
Why is this so difficult to grasp?
Dave
Jmmlc said:
Jean-Michel seems intent on not listening and confusing the discussion. I have never contradicted the claim that the HOM take a longer path, thats what they do. Hence the trace-velocity along the axis (as it is called in acoustics) is slower (longer path) although the wavefront moves at the same speed as all other waves. There is no dispersion (variable wave velocity) only diffraction (different wavefronts are created).
There was a study presented at AES on the directivity effect from the HOM by Gotfried Bueler at Achen. He concluded that they have a minimal effect on directivity and I would agree. But thats different than saying that they have a minimal effect on audibility. The two things are completely different.
I personally have no problem with Jean-Michel posting here, but it would be nice if he stayed on the subject and did not give misleading information and comments. I have said for dozens of pages that I see no way to compare his device to mine as they don't do the same thing. But Jean-Michel seems intent on making a comparison and I see none possible. If CD is not his goal, as it is mine, then we will certainly come up with different designs. What is so surprising about that?
Soongsc - you are making me angry now. This is totally unfair of you. You ramble on and on about things that you have no supporting data for and when someone makes a comment that you don't like you demand proof. If we were to demand proof from you for everything that you claim you would have nothing to say.
seh said:
On that I cannot comment other than some speculation (although that is rather rampant in this thread). I certainly can't exclude that particular possibility. I would say, though, with relative assurance, that this likely cannot be done with typical acoustic testings systems currently in use for loudspeaker measurement. In addition, at the frequencies in question and the environment of a waveguide, I also suspect that the mic itself may adversely alter the response if in close proximity, so the measurement may not accurately represent the wave motion in absence of the mic influence. Speculation, of course.
Dave
That is quite correct. I worked in underwater sound at Penn State where the torpedo sonar heads were developed. I know HOW to do it, I just don't have the capability. And in the end we already know that we don't want them and measureing them won't change that. At B&C I showed them how to measure the HOM from the drivers using microphones along a plane wave tube. The HOM in the horn could be done the same way. Since its axisymmetric, you only need a line of point measurements and you can sort out everything.
Theoretically you can measure the far field and calculate the mouth velocities - acoustic holography - and from that you could calculate the modes. But this method is highly prone to errors and singular or near singular matrices in the inversion process - we tried this several year ago. WIth enough computer power however the matrices could be analyzed with SVD, but basically it all requires a tremendous amount of effort, which in the end doesn't change what you want to do.
Theoretically you can measure the far field and calculate the mouth velocities - acoustic holography - and from that you could calculate the modes. But this method is highly prone to errors and singular or near singular matrices in the inversion process - we tried this several year ago. WIth enough computer power however the matrices could be analyzed with SVD, but basically it all requires a tremendous amount of effort, which in the end doesn't change what you want to do.
Dr. Geddes, since you have worked with B&C and you have shown them not only of the existence of HOMs but how to measure for them, wouldn’t it be relatively easy for them to take an existing driver like the DE250 and make a phase plug based on your patent assuming off-course you give them a license to do so?
Alternatively, would it be an expensive proposition to have them develop one for you to use on your loudspeakers as an OEM?
Sorry if this has been discussed before.
Alternatively, would it be an expensive proposition to have them develop one for you to use on your loudspeakers as an OEM?
Sorry if this has been discussed before.
musical noise said:
Yes, it would be expensive to get a custom driver made. If that were not the case I would have done it by now. Someday I will, but until then Ido the best that I can with what I have.
The point that I think that you are missing is how really insignificant good sound quality actually is in the marketplace. Its not about sound quality, its about image and what people "think" will sound good, and oh yes, does the cabinet "look good". Real sound quality does not driver the industry, in fact it hardly even rates at all.
Hello dlr,
As I interpret your sarcasm about my participation to the discussion, I guess that much what I could said, as it is not covered by peer review papers, as I have no measurements that you could agree with and as I have no any agreed protocol blind tests results to show and as only basics facts but no hypothesis are allowed here will be again criticized and ridiculized.
The main point of disagreement I have is that I am convinced that constant directivity as we can only maintained it above 1kHz (roughly) and as it require that we listen off axis is pretty useless in hifi use. In the best case constant directivity above 1kHz could be interesting if it was obtained by less diffraction. The pressure fields as were illustrated for the OSwaveguide in this thread are really bad. As we can see also the foam plug has very few action on the "interleaving" (crossing) of the response curves at different angles and that means that diffraction is faintly reduced by the foam plug.
Then I agree with the study begun by Soongsc in order to search for an intermediary between the horn and the waveguide that will deliver a smoother pressure field, without foam plug, at the depend of a less perfect constance of the directivity. I encourage him to develop his work.
Best regards from Paris, France
Jean-Michel Le Cléac'h
As I interpret your sarcasm about my participation to the discussion, I guess that much what I could said, as it is not covered by peer review papers, as I have no measurements that you could agree with and as I have no any agreed protocol blind tests results to show and as only basics facts but no hypothesis are allowed here will be again criticized and ridiculized.
The main point of disagreement I have is that I am convinced that constant directivity as we can only maintained it above 1kHz (roughly) and as it require that we listen off axis is pretty useless in hifi use. In the best case constant directivity above 1kHz could be interesting if it was obtained by less diffraction. The pressure fields as were illustrated for the OSwaveguide in this thread are really bad. As we can see also the foam plug has very few action on the "interleaving" (crossing) of the response curves at different angles and that means that diffraction is faintly reduced by the foam plug.
Then I agree with the study begun by Soongsc in order to search for an intermediary between the horn and the waveguide that will deliver a smoother pressure field, without foam plug, at the depend of a less perfect constance of the directivity. I encourage him to develop his work.
Best regards from Paris, France
Jean-Michel Le Cléac'h
dlr said:
Jmmlc said:
Here is the crux of the issue. You may be convinced, but that and all of your conclusions are based on speculation, none of it based on any established facts, peer reviewed or otherwise. You apparently admit to that here. I and others I'm sure would easily accept measurements or research that are cogent and supported by logic and/or theory. That has been severely lacking as I see it, others may decide for themselves.
I can't even say that I fully agree with all of Dr. Geddes conclusions, as I have not heard the system myself, but to me the data as presented is hard to refute without other hard data that demonstrably contradicts, which both you and I lack. Repetitive speculation is no substitute for data.
Dave
Hello Dave,
Speculation in my opinion is related to the attitude taken by someone who draw conclusions from his readings without having ever listening to what he is speaking.
I have myself listened to several 2 ways system using a waveguide in the mid + highs (with and without foam plug) and even if it was not Earl's one I can figure now why always I tried to avoid the brutal "hard data" effects of diffraction in the horns I have built along the 30 last years, such goal seemingly attained in what is known as the Le Cléac'h horn.
Best regards from Paris, France
Jean-Michel Le Cléac'h
Speculation in my opinion is related to the attitude taken by someone who draw conclusions from his readings without having ever listening to what he is speaking.
I have myself listened to several 2 ways system using a waveguide in the mid + highs (with and without foam plug) and even if it was not Earl's one I can figure now why always I tried to avoid the brutal "hard data" effects of diffraction in the horns I have built along the 30 last years, such goal seemingly attained in what is known as the Le Cléac'h horn.
Best regards from Paris, France
Jean-Michel Le Cléac'h
dlr said:
Hello, musical noise
Conical could have the least diffraction only if a spherical pulsating source should exist and could be attached to the throat of the horn and if the length of the horn could be infinite.
As those goals are not reached, praticaly, conical horns are one of the the worst case of diffraction.
I don't want to begin such a discussion as in Audioasylum... ;-)
http://www.audioasylum.com/forums/hug/messages/14/140852.html
And yes you are right the Le Cleac'h horn as you may be convinced looking to the smooth pressure field developping inside and outside the horn and to the very smooth frequency response curves on and off axis is a horn generating very few difffraction.
( see : http://www.diyaudio.com/forums/attachment.php?s=&postid=1771096&stamp=1236837246 )
Best regards from Paris, France
Jean-Michel Le Cléac'h
Conical could have the least diffraction only if a spherical pulsating source should exist and could be attached to the throat of the horn and if the length of the horn could be infinite.
As those goals are not reached, praticaly, conical horns are one of the the worst case of diffraction.
I don't want to begin such a discussion as in Audioasylum... ;-)
http://www.audioasylum.com/forums/hug/messages/14/140852.html
And yes you are right the Le Cleac'h horn as you may be convinced looking to the smooth pressure field developping inside and outside the horn and to the very smooth frequency response curves on and off axis is a horn generating very few difffraction.
( see : http://www.diyaudio.com/forums/attachment.php?s=&postid=1771096&stamp=1236837246 )
Best regards from Paris, France
Jean-Michel Le Cléac'h
musical noise said:
It's been a long time since I posted to this thread. I think back to page 4. Back then I said you cold not fill a thimble with my knowledge of wave guides. That is still pretty true. But i do have a couple of questions.
First I noticed that the profile of an OS wave guide is a hyperbola, at least in the throat and initial expansion regions before the profile is modified to blend smoothly into the baffle surface. This profile happens to be the that of flow or stream lines for the potential flow solution through an orifice.
It would seem that the OS wave guide is basically the right 1/2 of that picture with the profile set to a streamline that asymptotes to the correct exit angle (defining the profile hyperbola). So wouldn't the ideal diaphragm shape be that of an OS, i.e. the shape of a surface of constant velocity potential?
First I noticed that the profile of an OS wave guide is a hyperbola, at least in the throat and initial expansion regions before the profile is modified to blend smoothly into the baffle surface. This profile happens to be the that of flow or stream lines for the potential flow solution through an orifice.
It would seem that the OS wave guide is basically the right 1/2 of that picture with the profile set to a streamline that asymptotes to the correct exit angle (defining the profile hyperbola). So wouldn't the ideal diaphragm shape be that of an OS, i.e. the shape of a surface of constant velocity potential?
Hello Jean-Michel
In a conical flare the introduction of a spherical wave front will have no diffraction, that much is obvious and we’re in agreement. I will also concede that a spherical wavefront is not obtainable (at least not straight out of the comp driver). A transition at the throat area is then, in my view, the next best thing. The Le Cleac’h expansion as well as all others has a continuously expanding wall profile and therefore an axial wave will diffract.
I am sorry but pressure field simulations are just that, and I don’t base much stock on them either way. Real world measurements are usually much uglier than simulated results. Once again I don’t want to be argumentative but even if I was to take that picture at face value I don’t see how I could infer in it the absence of diffraction effects.