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#21 | |
diyAudio Member
Join Date: Apr 2005
Location: -
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It is good to see more numerical simulations and I will follow your progress with interest.
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ABEC uses flat zero-order elements which are the least accurate requiring higher numbers of elements to achieve a given level of accuracy but they are relatively easy to program and require the least computer resources per element. Generally where you will need to increase resolution in order to reasonably specify the problem with flat triangles are things like the tweeter surrounds and lips. For example, it is well known that diffraction from a non-recessed tweeter will create small but audible differences. This requires resolving with flat triangles if the simulation is to be accurate. |
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#22 |
diyAudio Member
Join Date: Jan 2009
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Thanks for following along
![]() According to the ABEC help file the Edge length should be at a minimum 1/2 x C / Mesh Frequency, which I have taken to be half the speed of sound divided by the highest frequency of interest. Which for the 12KHz in my sims works out to be 14.3mm. Which is why I have stuck to 10mm as the maximum on the front baffle and that seems to have been sufficient. The waveguide goes down to 5mm at the driver (throat) end as without sufficient resolution there the waveguide contour is not preserved. So I think your comments are a more informed expansion but not really at odds with what I said? |
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#23 | |
diyAudio Member
Join Date: Apr 2005
Location: -
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#24 |
diyAudio Member
Join Date: Jul 2007
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You don't think they look useful already?
__________________
Use Science to design your speakers and they will sound like a piece of Art... |
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#25 | |
diyAudio Member
Join Date: Jan 2009
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I would like to make the simulations as realistic as possible but I am already approaching a point of diminishing returns with resolution in ABEC. With the code you are used to you can probably just use whatever resolution you need and use a faster computer to crunch through it. In my experience with ABEC beyond 4,000 elements the solve time gets out of hand quickly and 10,000 elements seems to be a practical limit before there will never be a solution found in a realistic time frame. My laptop is faster than my server but I don't like to leave it on overnight that often so it tends to be used for less than 2 hour sims. I have no other need for a monster workstation and I'm not convinced it would be a solution even if I had one. If I expand the model to cover a complete baffle and woofer (which is in the works) then I am limited to half symmetry and the problem gets twice as bad. I personally think the simulations are quite useful as they are, I have had the benefit of seeing more of them in various different stages to know that these current ones look much more acceptable. There have been a few constructions made already where the results from ABEC at similar resolution to this matched reality well enough which gives me hope I'm not chasing ghosts. |
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#26 | ||
diyAudio Member
Join Date: Jan 2017
Location: Ottawa
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One thing that should be mentioned is that you are using Fusion and I am using FreeCad for the CAD work. FreeCad can easily capture the horn mouth outline to create a polyline wire with exactly all the edges and vertices. Your Fusion flow is merging multiple straight lines to form a single longer line (missing intermediate vertices). There may be someone familiar with Fusion that knows how to avoid this merge and preserve the polyline. |
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#27 | |||
diyAudio Member
Join Date: Jan 2017
Location: Ottawa
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#28 | |
diyAudio Member
Join Date: Jan 2017
Location: Ottawa
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How would you know when the mesh is fine enough to have an acceptable level of discretization errors. ? Since these are entire speakers, it's not really practical to use the same resolution everywhere. |
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#29 | ||
diyAudio Member
Join Date: Jan 2009
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![]() There are no controls in the extrude command that allow the polyline to remain. Using another command might be able to accomplish that but I think maybe not. If anyone has any suggestions I am open to try them. Quote:
Fusion does capture the exact outline through the mesh to BRep conversion it just refuses to keep the single line cuts where they form a straight line with the extrude command. So if that could be solved Fusion would be very easy. CAD programs are so different in terminology and layout that once you've learned one learning another can be frustrating. |
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#30 | |
diyAudio Member
Join Date: Sep 2004
Location: Prague, Czechia
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https://at-horns.eu Last edited by mabat; 26th July 2020 at 10:59 AM. |
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