I am not sure that is true. I just decided not to continue in the discussion. I did not believe you were making an effort to understand, you were just playing word games for your own amusement.
The blurred boundary comment is an interesting observation. One could consider the lumped parameter sealed box and ported box enclosures as just simplifications of TL modeling. A routine that can predict behavior of a TL enclosure can also model a closed or ported box, but not the other way around. A routine that can model a TL can also model a horn, or you could say that a horn calculator can also model a TL if stuffing is ignored.
All of these enclosures can be modeled by the same math and therefore you don't need to be concerned about boundaries of applicability between models. If you are using one of the simple T/S based models, then you really need to be aware of the limits of applicability with respect to geometry and frequency.
Once you step up to a 1D wave equation TL style of model, then you need to be concerned about the other two dimensions and potential standing waves not accounted for across the TL (side to side or front to back) at higher frequencies. The mitigating factor is the stuffing, it will help suppress the modes you are not accounting for in your model so your results will probably still be accurate.
With respect to Hornresp, Augspurger's TL program, AJHorn, and my MathCad worksheets; a few years ago I ran tests of my MathCad models against these three other programs. If the same problem was formulated and run the results matched very closely, physics is physics. Each program has its own set of strengths and weaknesses so the user needs to determine what they want to accomplish and then pick the right tool. The accuracy of model results is driven by the knowledge and skill of the user.
Has anyone tried this? COMSOL : Acoustics Module
I have access to a copy (it's very expensive). This does full 3D FEM on arbitrary geometries and it does multi-physics so the thermal effects at LF can be included.
I have access to a copy (it's very expensive). This does full 3D FEM on arbitrary geometries and it does multi-physics so the thermal effects at LF can be included.
Not intending to minimize or disagree with the point you're trying to make, Ed, but your description of the second graph is not quite correct IMO. The graph shows the system response with the red line, the outputs of the driver and terminus/port combined in both magnitude and phase, whereas the dashed blue line is how the system response would behave in an infinite baffle arrangement. You need to show the 8th graph in the series to accurately show how the driver and terminus/port individually respond where the red line is the driver and the dashed blue line is the terminus/port. At least that's my thoughts, and if I'm all wet, I apologize.
Paul
Paul
Just to move this along:
Vifa P17 Mass Loaded Quarter Wave designs
The above simulations use the same parameters for a subject driver. The top sim is intended to make use of room gain to arrive at a "flat" response in room. In my experience this response is less subject to "boom" due to room modes. YMMV
The bottom sim is an exercise in attaining a "flat" response from the baffle. The area under the red curve, above the blue dash line, is the gain of the system from the terminus.
It does linear acoustics, can couple to structures to an extent and can include some thermal effects. It does not simulate the full physics in particular the nonlinear fluid motion is not handled which limits the coupling to structures, acoustic dissipation and nonlinear effects, etc...
Yes of course FEM is the modern compute, and purchase cost intensive solution. However, one should study the classics for insight into the nature of different well known alignments. I would welcome having an FEM program available but would probably still mostly use T&S type simulators where they apply. Non-linear modeling is another story.
I agree and as I mentioned used hornresp to model a vented system with a long (30") port here. And of course a horn with no flare is a TL. It did not seem to be completely accurate but I believe that no losses are included:
AudioKarma.org Home Audio Stereo Discussion Forums - View Single Post - AK Design Collaborative - Insubnia
pkitt,
I appreciate your comments. Together, we'll get it right. I've added them to the things I'll review this weekend.
I'm looking forward to diyIndiana. Hope to see you there.
I appreciate your comments. Together, we'll get it right. I've added them to the things I'll review this weekend.
I'm looking forward to diyIndiana. Hope to see you there.
It seems there is a lot of work involved with the setup. Please let us know what you think.😀
I think that most of the FEA programs will handle acoustics. The problem is the cost and the learning curve. They use ANSYS here in China where I am at the moment and it does a good job, but of course they ripped off the software and they spent endless hours learning to use it. Then the problem is that it's not a flexible model when its done. It's A model, of A single design. Very detailed for that specific design, but not very extensible in terms of changing the model substantially. FEA has its good and bad points, but I still think the same way about it today that I did 40 years ago when I used it in my thesis: its too detailed and cumbersome for rapid development. Its fine if you are trying to squeeze out the last few pennies from a design, as would be done in automotive or the like, where millions of the same product are made. But I have hardly used it since my school days.
I replaced the ANSYS models here with a T-matix model which is far less detailed, but detailed enough, and runs instantly. It will even search hundreds of designs for the best one - something that FEA would have real trouble with.
My experience with ANSYS is similar to Earl's comments. I use ANSYS to model the air volume in the enclosure to calculate the natural frequencies and map the standing waves. I use it to check my MathCad model results. Where I ran into trouble was simulating a TL or horn with an opening to the room that was large enough the acoustic impedance boundary condition provided both mass and damping that were frequency dependent. I did not see away of doing this and could only apply the simple pressure equal to zero boundary condition. I could make the box models somewhat parametric so rerunning different dimensions was quick and easy. It was a good tool for checking my MathCad models but not so good for doing iterative detailed designs.
Yes, there are some friends around here that have had experience with various packages. The real power are over the $300K range if I remember correctly. Even those are in very specific areas. The packages most widely used are okay for looking at trends where more cost effective finalization in sample modification is applicable.
I published a paper about 25 years ago on how to load a finite FEA model with a realistic boundary condition. If you want to see how difficult that really is look up that paper in the AES - or take it from me - you don't want to do it that way.
The way that I discovered the OS waveguide was trying to find a feasible way to model a horn, knowing that a 3-D analytic solution was not possible with Websters Equation. I, like you, had tried the FEA packages but they just were not up to the problem at the time (much better today of course), but then I find a way to do a 3-D anayltical solution and that changed everything.
Sometimes the simple models turn out to be the most elegant and are still powerful enough to do the required design work. In my opinion, MathCad is an amazing tool for speaker design and in most cases can do a better job than bigger more expensive FEM packages.
Absolutely - MathCAD is my most useful program. I am however dismayed by the poor support from the new owners and I have become disgusted with the programs lack of support especially on the new platforms like Vista and Win 7. Only MathCAD 14 will run on these platforms and then it has bugs, and the new owners do not seem to care very much.
My technique is to model in MathCAD to get the math right and then move these algorithms to a windows based GUI. MathCAD can then be used for confirmation of the windows code, but the Windows GUI offers a lot more flexibility in operation.
I recently bought Mathmatica at a huge discount (home use) and find it to be an amazingly powerful program as well.
Agreed, the new owners of MathCad could not do more to kill a great product. When I upgraded to Version 14, I could not find a way to order and pay for the upgrade. The support is horrific from point of sale to existing user. I think they are getting the message, but their main interest is in the large cooporate sales and not the little individual users.
Back to TL's .....
Back to TL's .....
back to TLs indeed...what do you guys make of this?
below is a link to a strange idea i had just now.
http://www.diyaudio.com/forums/full-range/162967-open-backed-tapered-tl.html
would anyone be able to offer some insight into what effects this would have on response? pr alternatively be able to offer advice on how to model this successfully?
below is a link to a strange idea i had just now.
http://www.diyaudio.com/forums/full-range/162967-open-backed-tapered-tl.html
would anyone be able to offer some insight into what effects this would have on response? pr alternatively be able to offer advice on how to model this successfully?
Yes guys the FEA method appears to be the big hammer method, posing the problem properly is a lot of work.
BTW I assume it predicts that a wave will reflect off of the open end of a pipe 😀.
BTW I assume it predicts that a wave will reflect off of the open end of a pipe 😀.
An interesting set of comments and I suspect reasonably representative of those of the DIY speaker community? Tempted though I am to point out who got what wrong and why the problem seems to be more that people do not understand how to use the tool of numerical simulation effectively to gather information to guide their design. Nor, perhaps more relevantly, do most people seem to want to and shifting that viewpoint probably requires exposure to a few positive examples rather than being bashed for ignorance.
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