Application of Impulse Excitation for DML Design and Analysis

[Veleric]

Nice find Christian,
I did the algebra for the isotropic case and it came out to an aspect ratio of 5.07 to meet my proposed criteria of 1.3. LISA confirmed the same.
Luckily for me, my panels are not isotropic, so I don't need such an extreme aspect ratio. Also, clamped edges pushes the natural frequencies closer together than simple edges, so getting a little "clamping" action from the perimeter is not so bad in that respect.
I'll have to take a look at the orthotropic solution a little closer, and see if that can be converted to a relatively simple rule that applies for typical plywood properties.
Eric

 

[Deude_Mann]

What DSP do you guys use? From what Ive read, it seems the most versatile could be to buy one of the recent Pioneer or Onkyo home theatre systems with Dirac live, or Denon system with latest Audyssey app configurable from laptop. Lots of channels for crossovers or multipanel systems, plus subwoofer channel(s). Another option may be to put all music on a laptop and use a streaming software plus windows Equaliser APO, again feeding a multichannel home theatre system.

I doubt it's worthwhile going to true 'hifi' amplifiers as to get a system with multichannel and DSP would be very expensive, and I doubt that differences in distortion figures can be heard anyway. Noise may be an issue though in sub-hifi systems. And possibly power, as the way they quote power handling in the multi-channel systems is pretty bogus.

This thread on diyaudio is very interesting.
https://www.diyaudio.com/community/...controlled-integrated-dsp-amp-tas3251.325826/
They built a modular system that maintains a digital signal path (no multiple ADC/DAC as with eg the miniDSP) with one of the latest TI class D amplifier chips TAS3251. They adopted the design from the TI evaluation board for that amp, (which has been withdrawn from sale). But Im not sure I want to commit to that sort of effort/risk, which required soldering SMD by hand. Also the chips have very long lead times now, but it looks like a great solution. But if there was a bunch of people starting on the same project, I would be interested...

Paul

Parts-Express has a low-cost stand-alone option. Before anyone gets in a fit, I did not say it was the best, or the worst, but as DSP goes it's affordable.
Parts Express DSP
They also have some mini Class-D amps with built-in DSP that have plenty of power for home DMLs
Class-D with DSP


A lot of home receivers have a lot of the basic DSP functionality, and have for years, which means the used market is full of relatively low cost possibilities. For example I have an old Denon a friend gave me that has parametric EQ, active crossover, and time alignment. I also have a Yamaha I bought a long time ago (10 years?) that has DSP. From what I have seen here a unit with multiple parametric EQ per channel and active crossover would do most, maybe all that is needed for a DML; all of them have subwoofer out these days. The main thing IMO is that if you are looking for the nth degree of fidelity then you want one with a good ADC/DAC that samples at high bit resolution and frequency, higher than CD quality if you can find one.

FWIW In a car I use a MiniDSP C unit which granted is not cheap. That being said, there are multichannel amps with integrated DSP which include parametric EQ, active crossover, time alignment, etc. all integrated into the unit. Pioneer HUs, and now many others, also have integrated DSP.

 

[pway]

Deude,

Thanks yes I have seen those units and the minidsp.

Idk how much DSP affects the audible quality (suspect I would have difficulty hearing it) but if it does at all, I would think it best to avoid stand-alone dsp with analog in, where you end up having multiple DACS and ADCs.

I have a Denon amp now with dsp, and I have bought an after-market ipad app to configure it. Have not tried it much yet. But it’s not the latest model and cannot be controlled from laptop. Only the very recent ones allow you to control the curves properly afaik, and you pay a premium for that.

Paul

 

[Deude_Mann]

Yes agreed. When setting up a system I try to avoid multiple ADC DAC conversions. For example I use coax SPDIF (digital) to send the audio to the MiniDSP so there is only one stage of DAC (at the analog output to the amps).

 

[pway]

Agreed.
PS: I meant to say DAC, not DSP in the prev message. "Idk how much the DAC affects the audible quality...

 

[homeswinghome]

@pway
Hello Paul,
After the difficulties with code aster, I had a look to other possibilities including tools to solve PDE. I understood with that the plate PDE (Kirchhoff) is not "FEM friendly". On the Elmer side, it is clear the orthotropic materials are not supported in the 2D simulations. So I came to the conclusion that the FDM (Finite Difference) is not a so bad way... Let me know if you see new possibilities.
Christian

 

[homeswinghome]

@pway
Just to keep you inform : I have installed Fenics thanks to a docker container. Seems it runs just out of the box. I added on it Fenics shells which is a package dedicated to shells so plates... Seems also it runs. The tricky point is to understood the functionalities that are in PDE and FEM vocabulary... A bit obscure to me in first approach. Hopefully some examples are provided. Will see.
Christian

 

[pway]

@pway
Hello Paul,
After the difficulties with code aster, I had a look to other possibilities including tools to solve PDE. I understood with that the plate PDE (Kirchhoff) is not "FEM friendly". On the Elmer side, it is clear the orthotropic materials are not supported in the 2D simulations. So I came to the conclusion that the FDM (Finite Difference) is not a so bad way... Let me know if you see new possibilities.
Christian

Hi Christian
Sorry for the delay - Im finding it a bit hard lately to allocate time to this.

Not sure what you mean that plate PDE is not FEM friendly. I remember Elmer used the smitc technique to prevent 'locking', is that what you mean?. I think I read that code aster uses some other techniques to prevent the same phenomenon of convergence failure. But I doubt plate PDE is any more subject to this than other PDEs.

I think you've made great progress with the FDM, but I would prefer to stick with techniques which have been validated, and can accomodate any shape or support condition.

Elmer almost supports orthotropic, it just requires a bit more code to be added, which they won't do unless its attached to a project or funding. One response I had from Kevin Arden on the Elmer forum had him adding that extra code by another mechanism. He said it worked, but I didn't pursue it because I didn't want to open yet another can of worms:

I was able to copy the Smitc.F90 solver to my working directory renamed
MySmitc.F90
added a subroutine, and forced the code to call it. I hard coded the Ematrix, and received the correct solution.
I then modified the E22 and E33 terms and the answer changed accordingly.

I copied the perforated subroutine, but hard coded the Ematrix instead of letting the original code calculate it.
Not an ideal solution, but seems to work.

I have not been back to Code Aster, are you convinced it is a non-starter for you? If so, there is no point in me pursuing it further.

Paul

 

[pway]

@pway
Just to keep you inform : I have installed Fenics thanks to a docker container. Seems it runs just out of the box. I added on it Fenics shells which is a package dedicated to shells so plates... Seems also it runs. The tricky point is to understood the functionalities that are in PDE and FEM vocabulary... A bit obscure to me in first approach. Hopefully some examples are provided. Will see.
Christian

There are examples of using Fenics here https://computational-acoustics.gitlab.io/website/
I think it may be made by the same people as bempp.

I read through the first couple of tutorials, it seems mathematical grounding is needed (but the same is true of bempp, and I managed to get results from that).
At this point, I have a bunch of half-finished bits and pieces I want to get back to, so I may just go my own way with isoptropic Elmer + bempp. I'm in danger of losing the threads if I try anything else I think. I just need to find some time, I need to be more focused...

I would be happy to try Fenics if you make progress on that .

 

[homeswinghome]

Hi Christian
Sorry for the delay - Im finding it a bit hard lately to allocate time to this.

Hello Paul
Don't worry. We have all our lives and priorities to manage. This is a DIY so leisure time topic

Not sure what you mean that plate PDE is not FEM friendly. I remember Elmer used the smitc technique to prevent 'locking', is that what you mean?. I think I read that code aster uses some other techniques to prevent the same phenomenon of convergence failure. But I doubt plate PDE is any more subject to this than other PDEs.

I read in different documents (Scikit-fem, Fenics?) that the PDE of plate being of the 4th order (biharmonic), their transformation by the FEM approach (trial function + integral) leads to discontinuity. It can be solved by specific finite elements and some advanced transformation of the standard initial PDE. My knowledge in FEM is too weak to make a precise synthesis.

I think you've made great progress with the FDM, but I would prefer to stick with techniques which have been validated, and can accommodate any shape or support condition.

I understand and I have in mind what you want to do with non rectangular shape. You're right to highlight the validation question. We saw some posts ago the interest to compare results. I continue to search for an FEM alternative.

Elmer almost supports orthotropic, it just requires a bit more code to be added, which they won't do unless its attached to a project or funding. One response I had from Kevin Arden on the Elmer forum had him adding that extra code by another mechanism. He said it worked, but I didn't pursue it because I didn't want to open yet another can of worms:

Yes, I saw the answer you get in the Elmer forum. Let's keep an eye on it.

I have not been back to Code Aster, are you convinced it is a non-starter for you? If so, there is no point in me pursuing it further.

I was really disappointed with Code Aster. As I don't want to have at the top of the questions "how to make the tool working on my computer?", it is a no go for me.

 

[homeswinghome]

There are examples of using Fenics here https://computational-acoustics.gitlab.io/website/
I think it may be made by the same people as bempp.

Thank you to remind us this source!

I read through the first couple of tutorials, it seems mathematical grounding is needed (but the same is true of bempp, and I managed to get results from that).

This is the difficulty! Solid physics and mathematical basis are needed. My hope for starting is to find examples close enough to what we search just to have to make some variations in the way the results are used. Second hope is to find some documents that will demystify the mathematical form.

At this point, I have a bunch of half-finished bits and pieces I want to get back to, so I may just go my own way with isoptropic Elmer + bempp. I'm in danger of losing the threads if I try anything else I think. I just need to find some time, I need to be more focused...

I would be happy to try Fenics if you make progress on that .

I will inform on the progress or... the non progress!