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Old 5th July 2009, 02:42 AM   #5921
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Default what's the difference??

Quote:
Originally posted by mige0



Thanks John for pointing to that.

Where do you see the main differencies - I mean as a visualisation tool as I used it for acoustic wave front propagation / wave front bending / interference pattern?


Michael

For one thing it's more or less two dimensional at best...

John L.
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Old 5th July 2009, 03:21 AM   #5922
gedlee is offline gedlee  United States
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Quote:
Originally posted by john k...
Please do not confuse ripple tank simulations as being represenative of acoustic wave propagation. The ripple tank yields surface wave results (or sgallow water waves). These are not the same as waves propagationg in free space. See for example:
Hi John

The Falstad apps are quite useful, I use them in my physics class all the time. The "ripple tank" applet actually solves the wave equation in 2D, its not a water wave at all (which is different from a sound wave). He just uses that name because it sounds "catchy" - the sims are quite accurate for what they are. But you are quite corect that 2D can sometimes be misleading. For example a 2D cross section of a 3D axisymmetric waveguide WILL NOT be accurate. There is no way to do an accurate 3D problem in 2D, its always an approximation.

But heck, who cares about "reality" its just too much fun playing with the software.
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Old 5th July 2009, 06:27 AM   #5923
mige0 is offline mige0  Austria
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Default Re: what's the difference??

Quote:
Originally posted by auplater



For one thing it's more or less two dimensional at best...

John L.

What would you say about the shape of a wave front in one plain - isn't it *exactly* "a two dimensional at best"?
So I don't see why to complain.


Quote:
Originally posted by gedlee


Hi John

The Falstad apps are quite useful, I use them in my physics class all the time. The "ripple tank" applet actually solves the wave equation in 2D, its not a water wave at all (which is different from a sound wave). He just uses that name because it sounds "catchy" - the sims are quite accurate for what they are. But you are quite corect that 2D can sometimes be misleading. For example a 2D cross section of a 3D axisymmetric waveguide WILL NOT be accurate. There is no way to do an accurate 3D problem in 2D, its always an approximation.

But heck, who cares about "reality" its just too much fun playing with the software.

You are mixing things and again are simply talking down any attempt to bring in some light to diffraction impacts other than your beloved math.

But as you have already joined the topic may I ask you the same question:

- Where do you see the main differencies - I mean as a visualisation tool as I used it for acoustic wave front propagation / wave front bending / interference pattern?


Michael
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Old 5th July 2009, 10:36 AM   #5924
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Actually, as long as it is recognized that the solutions are 2-D I would wirthdraw my objection. It can be shown that the shallow water equations yield the same wave linear equation as those for a compressible gas. The only questions would be what the details of the simulations are; dimensions, wave speed, wave number, etc.

[edit] But I would also agree with Earl that there is danger in assuming what you do in 2-d has any connections to what happens in 3-d. As a demonstation that edges and boundaries mess things up they are find, but the degree to which diffraction and reflection enter the pictide is another thing. These appletes are basically educational toys. If they help gain insight, fine.
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Old 5th July 2009, 11:41 AM   #5925
mige0 is offline mige0  Austria
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Quote:
Originally posted by john k...
...but the degree to which diffraction and reflection enter the pictide is another thing.
Thanks John for your clarification.

Yes, its first hand do gain insight / understanding and second about the "degree to which diffraction and reflection enter the pictide" in terms of comparable numbers


Until now I haven't found a tool that does this "degree to which diffraction and reflection enter the pictide" correct - CARA is mere ray tracing (though with smashing results when working around with some tricks) and BEM doesnt show what's going on either.

On the other hand there is a lot of confusion going on about the very mechanisms involved and how they translate.

Earl's statements are of little help as he is confused the most when it comes to this very topic - no "real" understanding IMO - just giant general knowledge and some impressive math juggling for the sake of a "rigor single spec optimisation".

Hence I do not understand what he wants to tell me and he does not understand what I'm after.


Michael
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Old 5th July 2009, 12:22 PM   #5926
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Default Re: Re: what's the difference??

Quote:
Originally posted by mige0



What would you say about the shape of a wave front in one plain - isn't it *exactly* "a two dimensional at best"?
So I don't see why to complain.


...yes, it may be a 2D representation of wavefront behavor, but (by necessity) it will ignore any confounding from the Z axis solutions, hence it does not represent 3D space, and as John K says the danger is in misinterpreting this as reality for sound waves

Quote:
Originally posted by mige0


You are mixing things and again are simply talking down any attempt to bring in some light to diffraction impacts other than your beloved math.

But as you have already joined the topic may I ask you the same question:

- Where do you see the main differencies - I mean as a visualisation tool as I used it for acoustic wave front propagation / wave front bending / interference pattern?


Michael
I don't see Earl talking down at all... just stating reality...
as a visualization tool for diffraction of 2D waves ok... but we don't listen to 2D waves, sound waves are 3D, and since you seem to want to predict audio performance using sims, I don't see the application as representing anything accurate in doing so...

John L.
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Old 5th July 2009, 01:02 PM   #5927
mige0 is offline mige0  Austria
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Default Re: Re: Re: what's the difference??

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Originally posted by auplater



... just stating reality...


John L.

there is no "reality" in *any* allegory or equation - lets face it...



Michael
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Old 5th July 2009, 03:22 PM   #5928
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Default Re: Re: Re: Re: what's the difference??

Quote:
Originally posted by mige0


there is no "reality" in *any* allegory or equation - lets face it...


Michael
yes... equations have limitations as well... but until you demonstrate some understanding of the mathematical approach to modelling sound transmission, rather than dismiss it, your approach has less credibility...

John L.
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Old 5th July 2009, 03:58 PM   #5929
mige0 is offline mige0  Austria
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1 +1 = 2

need more?


Its not exactly "equations have limitations" that I'm concerned about with Earl's math - he is for sure brilliant in this - but - he has had some severe misconcept about the terms of "soundfield" and "wave front" (*and* to some other topics we went through in the past) that lead me to question what exactly he set up as the ancillary conditions to solve the equations.

This is where we need some more "real" understanding in the first place - no?



Michael
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Old 5th July 2009, 07:25 PM   #5930
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I think this thread is long overdue. Mostly internal mirror looking. Like this last write up with claims not at all documented as to what is estimated or how. But maybe blueprints can be estimated ?

This can be seen as tragic or just as a case among a lot of others when nothing is to be achieved but more to provide a playground. And yes of course, it's just a hobby !

/Erling
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