This looks very wierd.However, it is an interesting perspective.
The coarseness of the mesh is causing some serious aliasing, thats why it looks wierd. Its a useless plot because of this coarse mesh.
I'm confused here! If the piston is 3-4" how can the throat be 1" or 2"?
If you have two waveguides of identical shape except for the throat, and the throat has a piston whose size is matched to the throat then theoretically they will have the same directivity at all frequencies.
If the piston is greater than the throat and there is a phase plug, the phase plug will determine the final result, but in general the 2" throat will beam sooner than the 1".
You need to think about what happens at the edges of the throat when the diaphragm is larger than the throat. At LF this is not important, but at HFs it is everything. Draw it out and look at what has to happen as the diaphragm moves. This is why there are phase plugs and phase plugs determine almost everything about the HF performance.
If you restrict the range to 0-.1 you can get some useful data from the phase plot.
If for instance you use a flat 40mm. Piston then all of the phase wavefronts up to 10kHz. Are circular in form.
This represents the Hermetian limit of solutions to the paraxial wave equation for a flat piston of this diameter, and the wavefronts become non circular above this.
Rcw.
If for instance you use a flat 40mm. Piston then all of the phase wavefronts up to 10kHz. Are circular in form.
This represents the Hermetian limit of solutions to the paraxial wave equation for a flat piston of this diameter, and the wavefronts become non circular above this.
Rcw.
Hi soongsc,
I think you are probably right about there being a bug in the software. I would expect phase contour plots to look more like the following attached exponential horn examples.
Kind regards,
David
Attachments
Pure phase plot is going to be different from running a wave. One indicates only phase angle, but the other shows amplitude. Problem with AxiDriver seems to be how it swaps between +/-180 deg, and also display at various scales. The wave lengths and contour just changes. The higher the frequency, the funnier it looks.
I agree that the mentioned equation is not directly relavent to the current problem, but I just mentioned it because I found it useful to check that the software is delivering accurate data.
I found the phase plot accurate as far as wavefront goes appart from the ragged looking bits.
These might well be Thom effect artefacts.
rcw.
I found the phase plot accurate as far as wavefront goes appart from the ragged looking bits.
These might well be Thom effect artefacts.
rcw.
Wow, I hope that terminology "down under" isn't completely obscured from the rest of the world, because I virtually never understand what you are saying - I have never heard most of the terms and concepts that you use. And when I look them up they never seem to have anything to do with the problem at hand.
I have a vast experince in acoustics in NA, SA and EU and in all those localities the terminology is identical, but vastly different that what you come up with.
I have never heard of the "Thom Effect" and perusal of Google shows up nothing even remotely connected to acoustics. Just like most of your references.
As I have said previously my background in acoustics is only via seismolgy and that is via the acoustic approximation used in that field.
I seismologists and seimic tomographers know well what I am saying, since these things I refer to are used in this field and give access to a large variety of useful mathematics that is otherwise not available by only looking at the classical formulation of acoustics.
The approach that I have is certainly not from the classical acoustics viewpoint, but the mathematical methods I mention are never the less correct and relavent to the problems put forth in these threads in these forums.
By the Thom effect I refer to the behavoir of certain types of polynomials in the viscinity of singularities, usually referd to as Thom's catastrophe theory, this is much used by computer modellers and I am surprised you haven't heard of it.
rcw
I seismologists and seimic tomographers know well what I am saying, since these things I refer to are used in this field and give access to a large variety of useful mathematics that is otherwise not available by only looking at the classical formulation of acoustics.
The approach that I have is certainly not from the classical acoustics viewpoint, but the mathematical methods I mention are never the less correct and relavent to the problems put forth in these threads in these forums.
By the Thom effect I refer to the behavoir of certain types of polynomials in the viscinity of singularities, usually referd to as Thom's catastrophe theory, this is much used by computer modellers and I am surprised you haven't heard of it.
rcw
If anyone is interested, I have posted measurements of a horn with and without foam today. Of particular interest is that the horn is a real wonky one, which should generated gobs and gobs of HOMs. Therefore, the effect of the foam may be more easily discerned.
Here's the thread:
http://www.diyaudio.com/forums/showthread.php?t=151376
Well, as you know I'm following a slightly different path here – trying to look at the whole complex of diffraction where horns, wave guides and edge-diffraction have it's very roots in.
Even for some widely spread misinterpretation of the mechanisms of dampening measures (to "avoid" edge diffraction) we can gain a deeper understanding that for some might offer surprisingly conclusions.
In German language we possibly have it slightly easier from the very beginning, as "diffraction" here is rather called "Beugung" with the meaning of "bending" (though "Streuung" - the "spreading, scattering" meaning of diffraction can be used as well).
This indicates – in a simple understanding - that "diffraction" mainly tells us that you can hear a source that is hidden by a solid obstacle – meaning the wave front is "bent" around a corner.
Actually the term "diffraction" in audio does not have a scientific quantification – and is not even well defined for its very quality – at least as far as I know and telling from all the mess with this term I read around here – and I strongly advocate to *not* use it for the effects but rather for the cause *only*.
Doing so we will be able to more easily sort things out and we also see that for a piston source radiating into 2Pi space (infinite baffle) for example, the "diffraction" is always the same : 90 degree towards either side – no matter if we mount our speaker flush or put some sort of baffle rounding or horn in between.
What makes all the difference regarding the outcome (the *effects*) of that same 90 degree "diffraction" is how "points of diffraction" actually are aligned to form that 90 degree contour.
I have shown – in an structured manner – how diffraction of flush mount piston sources in infinite baffle turns out at:
http://www.diyaudio.com/forums/showpost.php?p=1891535&postcount=418
In my next postings I like to present how diffraction for simple round overs' of piston sources into infinite baffle turn out
In
http://www.diyaudio.com/forums/showpost.php?p=1924924&postcount=472
I have presented how different diffraction alignment (round over) at the mouth of a horn turns out.
And I possibly will present some more simus about how different diffraction alignment at the throat of horns turns out (looking some closer at scattering junctions).
Over the course my work hopefully provides a useful bunch of information that can be cross correlated and allows us to develop a basic feeling and understanding about the topic of "diffraction" on a more objective basis than has been available until.
It certainly has transformed *my* understanding in that horns have to be seen as "diffraction aligned" device – by far superior compared to direct radiators - in most but few cases - if considered in this context of sound filed defects
I strongly agree with thend to recognise sound field defects as "new" kind of distortion – possibly best to be called "distortion of time of arrival consistency" (TAC distortion)
Michael
PS
Again,
besides it's beauty the plots to be shown present a awful lot of information in a highly concentrated manner.
If needed you can familiarise with that kind of plots in:
http://www.diyaudio.com/forums/showthread.php?postid=1888195#post1888195
PPS:
BTW Soongc, your most recent simus in
http://www.diyaudio.com/forums/showpost.php?p=1916139&postcount=3265
are impressive again!
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