http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-408.html#post2104959
From what we see here, it is obvious why all of my builts never expanded that wide, even with the elliptical WG that I first tested.
From what jzagaja has shown, it seems the driver model has more influence on the directivity rather than the horn/guide. All of them are beaming.
From what we see here, it is obvious why all of my builts never expanded that wide, even with the elliptical WG that I first tested.
From what jzagaja has shown, it seems the driver model has more influence on the directivity rather than the horn/guide. All of them are beaming.
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Hmm, how about the fact that an elliptical OS waveguide need to have some kind of exponential hyperbolic like curved shape
I suppose that the shape/form of surface has some influence ?
Looks to me like an elliptical OS waveguide could easily appear to look much like a JMLC shape
Or is my old math a bit rusty
I suppose that the shape/form of surface has some influence ?
Looks to me like an elliptical OS waveguide could easily appear to look much like a JMLC shape
Or is my old math a bit rusty
From a limited point of view you might be correct – but as outlined quite often – diffraction is always the same (for 2Pi / 4Pi respec) and what counts is not *lowest diffraction* at a certain area but *best alignment of diffraction*.
In this sense the "change in curvature" actually *does* count. In the case under discussion at the transitioning point from a more or less conical contour into a round over of whatever sort .
Simply put – the pure conical part of the oblate spheroide contour the is kinda "waste" of horn length as there is no diffraction happening .
This part is also the root cause of the on axis sound field defect – the remaining problem with OS contour as a "constant beam width" approach.
I was thinking along these lines for a while now, but haven't got the time to do a lot of simus to tweak my Gaussian MinPhase contour accordingly.
The impressive work of that Australien guy I take as an inspiration to start again – thanks a lot for pointing there Jean-Michel.
As for the "superiority" of different "mouth" round over's, I suggest you just revise some of the simus I have shown on the topic ....
Bottom line it's the whole contour that makes up for good performance not the round over alone - *diffraction alignment* you remember?
Michael
You're welcome David.
Not knowing whether lip shape is of significance in HornResp, but in AxiDriver, it does make a significant difference.
WG/Horn should be driver specific.Are you joking?
Dan
An externally hosted image should be here but it was not working when we last tested it.
Nice comparisons so far !
Sure – but you immediately introduce on-axis sound field defects due to the quasi-straight contour part. It can even be seen at the relatively rough traces you show. Lowering the ratio of the quasi- conical part with respect to the whole contour, immediately improves this on-axis defect – and vice versa of course.
*If* you focus on that very behaviour of conical horn contour, you can see that effect also here (if you would re-scale the contours properly) :
http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-79.html#post2088873
Michael
Sure – but you immediately introduce on-axis sound field defects due to the quasi-straight contour part. It can even be seen at the relatively rough traces you show. Lowering the ratio of the quasi- conical part with respect to the whole contour, immediately improves this on-axis defect – and vice versa of course.
*If* you focus on that very behaviour of conical horn contour, you can see that effect also here (if you would re-scale the contours properly) :
http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-79.html#post2088873
Michael
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Dr.Geddes, I have something I have been thinking about, and wonder what you may think about this idea? I'm reminded about an article in a stereo mag I saw way back when, about B&W using the golf ball dimple technique on their ports etc..
What would the effect be I wonder on the first few inches of a Wave Guide, or along the pipe part in other types of horns? Or maybe even have the whole Wave Guide covered in dimples golf ball style ? Whatever the math or listening would dictate etc..
How do dimples in golf balls affect their flight?: Scientific American
I just wonder if it would help to release the sound waves better, and allow them to flow along the guide or horn easier than a smooth surface does etc?
There would be tons of modeling to do, as different dimple depths and sizes have differing results etc..
What would the effect be I wonder on the first few inches of a Wave Guide, or along the pipe part in other types of horns? Or maybe even have the whole Wave Guide covered in dimples golf ball style ? Whatever the math or listening would dictate etc..
How do dimples in golf balls affect their flight?: Scientific American
I just wonder if it would help to release the sound waves better, and allow them to flow along the guide or horn easier than a smooth surface does etc?
There would be tons of modeling to do, as different dimple depths and sizes have differing results etc..
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a thinker from outside the box.and allow them to flow along the guide or horn easier than a smooth surface does etc?
There would be tons of modeling to do, as different dimple depths and sizes have differing results etc..
Well done, keep ideas like this flowing.
I don't care if some of them don't work or even do the opposite to what is expected.
If we don't have ideas we cannot experiment and the hobby never moves on.
Congrats.
The purpose of the dimples on a ball is to keep the air flow around the boundary layer attached to the ball by converting the flow from Laminar flow to turbulent. It creates a surface behind the ball of low pressure, reducing drag on the ball, and increasing it's flight.
The function in a port is fairly similar. There are two places where problems arise with port overloading. The first place is the edges of the tube, this is where the dimples work. If a turbulent layer can be created, then the air will follow the port flare as it exists allowing a less turbulent transition during the pressure change. The other area that ports overload is the core, but Dimples have no impact on this, nor does the flare. The core load is solely dictated by the diameter of the port.
So what is being suggested here is to intentionally create turbulence around the edge of the waveguide by converting the soundwaves from a laminar to turbulent flow. This means that sound travels through the air traveling at the same speed and direction at all times, in a smooth and predictable fashion. We would then introduce turbulence which would then create differences in the speed and direction of airflow. From this point of view, I would think that the introduction of turbulence would create irregular sound waves at the edges of the pattern.
However, related to this, I've heard a rough surface can be a good thing, but I'm not really sure why. Maybe dimples sized to be smaller than the highest fundamental would be necessary to ensure no audible interference.
The function in a port is fairly similar. There are two places where problems arise with port overloading. The first place is the edges of the tube, this is where the dimples work. If a turbulent layer can be created, then the air will follow the port flare as it exists allowing a less turbulent transition during the pressure change. The other area that ports overload is the core, but Dimples have no impact on this, nor does the flare. The core load is solely dictated by the diameter of the port.
So what is being suggested here is to intentionally create turbulence around the edge of the waveguide by converting the soundwaves from a laminar to turbulent flow. This means that sound travels through the air traveling at the same speed and direction at all times, in a smooth and predictable fashion. We would then introduce turbulence which would then create differences in the speed and direction of airflow. From this point of view, I would think that the introduction of turbulence would create irregular sound waves at the edges of the pattern.
However, related to this, I've heard a rough surface can be a good thing, but I'm not really sure why. Maybe dimples sized to be smaller than the highest fundamental would be necessary to ensure no audible interference.
I also thought of what could be the benefit of using the golf ball dimple effect on sheets of cabinet material? So you build a horn or a tapered line etc, and the internal material part for the cabinet of the horn or tapered line etc, would be covered in the dimples.. So just picture a sheet of plywood where one full side is covered in the dimples, and that part makes up the interior portions of the cabinet..
Perhaps it could help the sound waves travel out the horn or line less fettered in some way, or at least certain wavelengths may travel easier ?
Anyhow I'm not sure, it's just an idea and one would have to try it.. I would be curious to know what would happen with one of Dr. Geddes WG's , if it were totally covered ,or just the first few inches in golf ball style dimples?
It would be easy enough to try, and also measure, by careful and patient drilling of the golf ball like dimple's on a WG, and then measure it.. Maybe trying just the first few inches first, then expand from there..
Dr.G if you try it, and it shows some sort of benefit SQ wise, that would be pretty cool, especially if it was one of my ideas that panned out lol
And no I don't play golf
Perhaps it could help the sound waves travel out the horn or line less fettered in some way, or at least certain wavelengths may travel easier ?
Anyhow I'm not sure, it's just an idea and one would have to try it.. I would be curious to know what would happen with one of Dr. Geddes WG's , if it were totally covered ,or just the first few inches in golf ball style dimples?
It would be easy enough to try, and also measure, by careful and patient drilling of the golf ball like dimple's on a WG, and then measure it.. Maybe trying just the first few inches first, then expand from there..
Dr.G if you try it, and it shows some sort of benefit SQ wise, that would be pretty cool, especially if it was one of my ideas that panned out lol
And no I don't play golf
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Doing something with the surface of the waveguide is not something that I have not thought about. But I do agree with Noah here that one cannot extend the ideas for high flow velocity to waves, since the mean velocity is zero.
The second problem is simple its very difficult to even test this idea.
So the bottom line is, while there may be a benifit, its not at all clear that there would be one or why and its almost impossible to do anyway.
I have tested a waveguide with smooth wals and one with a rough coat of paint. No real differences at all. But that just one test surface.
Well it's just one of those ideas that sits on the brain type of thing lol.. I thought of a way to do it, but if it's not worth trying I can relate.. One could maybe purchase a sheet of the outer golf ball material from a factory that makes them, then just glue the strips onto the WG or Horn etc.. I guess the few extra millimeters of material height now added, would screw things up anyhow lol..
K, I shall go back inside the box
K, I shall go back inside the box
No its a great idea, as I said, I've guven it consideration and most importantly I haven't rejected it. I just can't figure out how to test it in a practical way.
But the change in dimension, as you mention, particularly at the throat, does concern me. I do know from numerous tests that a bad fit at the throat has a big effect. This leads me to believe that the effect of the dimples here would be the most pronounced, but its hard to say if that would be positive or negative.
I was concerned about paint on the skin and how a rough surface (orange peel, etc.) might effect the performance and I found that this was negligable if the paint was not down in the throat.
The issue is certainly one of size - what size would one use? And should the perturbations be circumferential or axial? Or both?
What I do, is look for problems in what I have and attempt to specifically fix those with the most reasonable solutions. I consider the on-axis hole to be the greatest problem. Perturbing the mouth, with dimples, if you will, but big ones, might be just the right thing to break up the coherence of the response hole without having a major detrimental effect on anything else.
Elliptical also has merits - maybe. The jury is still out on that as well.