> I use ANSYS at work. I called and asked for a price once - I think it was in the
> neighborhood of $80k for what I wanted (all the solvers). They would also lease
> it to you for a similarly outrageous price (I don't remember what, but it was in
> the $10k-$30k a year range, I'm pretty sure).
I can confirm these are typical quotes for this type of software with support. However, similar software is freely available from other sources if you go looking for it. It may not be as slick and would require a modest amount of computer literacy to use (i.e. compiling codes, understanding file formats, etc...). But if it is a hobby and the code is free it would seem fit for purpose.
> The question is when does one stop?
It stops when the information gained is not worth the effort put in. Numerical simulation is best used to determine how something works or why something is wrong and how to correct it. Listening and measurements do not give you this information. What listening and (reliable!) measurements give you is information on actual performance.
> Actually, a few years ago I wrote an add-on for my worksheets that treated
> room reflections. It was limited to a rectangular room but could account for
> carpet on the floor, walls, and ceilings. The reflections coefficients were functions
> of frequency and the summation was reasonably quick. This is when I stopped
> worrying about every little ripple in the calculated response of a speaker.
Room effects are large but the ear does not "hear" what a microphone measures in a room. The brain is used to hearing sound in enclosures and interprets direct and reflected sound differently. There is a good chance, subject to the room, that the ear will "hear" those little ripples [in the direct sound] in the calculated response of a speaker.
> You could model a speaker in a room, but the problem you would run into would
> be the size of the model at high frequencies. You generally need the element
> size to be 0.2 times the wavelength of the frequency you're interested in or
> smaller, so if you want to go up to a high frequency in a large room, your model
> gets huge.
Resolving every nuance of the complete high frequency spectrum is computationally intractable in a room. However, it is also rarely necessary to solve engineering problems. There are statistical approaches which work fairly well at high frequencies where the modal density is high, FEM/BEM works well for low frequencies but the bit in the middle can be problematic.
> I am playing with a supertweeter model at the moment, and I am modeling in
> 2D, axisymmetric (a simplification from 3D obviously). I am also just modeling a
> small sphere around the tweeter. My model size is around 300MB, and a one
> freqeuncy solution produces around 8.5GB of data in about 2.5 hours. Each
> additional frequency doubles the time requirement and adds about 700MB of
> data storage requirement. This is on a 3GHz P4 computer with 1GB of ram.
I guess this defines the practical limit of what can be done in support of ones hobby.
Perhaps I should add that you are not using the optimum numerical approach for the problem being solved. For an external radiation problem of the type you describe a Boundary Element Method is going to be more accurate, require less computational time, give you an answer throughout space and require only the meshing of the external geometry of the supertweeter.
> neighborhood of $80k for what I wanted (all the solvers). They would also lease
> it to you for a similarly outrageous price (I don't remember what, but it was in
> the $10k-$30k a year range, I'm pretty sure).
I can confirm these are typical quotes for this type of software with support. However, similar software is freely available from other sources if you go looking for it. It may not be as slick and would require a modest amount of computer literacy to use (i.e. compiling codes, understanding file formats, etc...). But if it is a hobby and the code is free it would seem fit for purpose.
> The question is when does one stop?
It stops when the information gained is not worth the effort put in. Numerical simulation is best used to determine how something works or why something is wrong and how to correct it. Listening and measurements do not give you this information. What listening and (reliable!) measurements give you is information on actual performance.
> Actually, a few years ago I wrote an add-on for my worksheets that treated
> room reflections. It was limited to a rectangular room but could account for
> carpet on the floor, walls, and ceilings. The reflections coefficients were functions
> of frequency and the summation was reasonably quick. This is when I stopped
> worrying about every little ripple in the calculated response of a speaker.
Room effects are large but the ear does not "hear" what a microphone measures in a room. The brain is used to hearing sound in enclosures and interprets direct and reflected sound differently. There is a good chance, subject to the room, that the ear will "hear" those little ripples [in the direct sound] in the calculated response of a speaker.
> You could model a speaker in a room, but the problem you would run into would
> be the size of the model at high frequencies. You generally need the element
> size to be 0.2 times the wavelength of the frequency you're interested in or
> smaller, so if you want to go up to a high frequency in a large room, your model
> gets huge.
Resolving every nuance of the complete high frequency spectrum is computationally intractable in a room. However, it is also rarely necessary to solve engineering problems. There are statistical approaches which work fairly well at high frequencies where the modal density is high, FEM/BEM works well for low frequencies but the bit in the middle can be problematic.
> I am playing with a supertweeter model at the moment, and I am modeling in
> 2D, axisymmetric (a simplification from 3D obviously). I am also just modeling a
> small sphere around the tweeter. My model size is around 300MB, and a one
> freqeuncy solution produces around 8.5GB of data in about 2.5 hours. Each
> additional frequency doubles the time requirement and adds about 700MB of
> data storage requirement. This is on a 3GHz P4 computer with 1GB of ram.
I guess this defines the practical limit of what can be done in support of ones hobby.
Perhaps I should add that you are not using the optimum numerical approach for the problem being solved. For an external radiation problem of the type you describe a Boundary Element Method is going to be more accurate, require less computational time, give you an answer throughout space and require only the meshing of the external geometry of the supertweeter.
Ron E said:
From a sound field point of view, if you can see the dispersion of waves at various frequencies, that would probably be enough.
From a signal reporduction point of view, if you can get results to adentify non-linear regions so that you can optimize driver design, then that might be enough.
How about CAE Linux live-DVD ?
http://www.caelinux.com/
I am interested a in linaeum & Aero -kind of bending wave "planars" and this Live DVD seems to be a dream come true. Don't know yet if I have enough skills and/or computing power to calculate membrane resonance, radiation pattern and frequency response for such elements but CAE Linux looks extremely good live-DVD for any FEM applications.
http://www.caelinux.com/
I am interested a in linaeum & Aero -kind of bending wave "planars" and this Live DVD seems to be a dream come true. Don't know yet if I have enough skills and/or computing power to calculate membrane resonance, radiation pattern and frequency response for such elements but CAE Linux looks extremely good live-DVD for any FEM applications.
Thanks for the link. I was not aware that someone had put together a collection of CAE programs and this looks a reasonable set. There is even a bit of a community with people talking to each other.
On the other hand, apart from dynamic FEM (solving exactly what I have not yet determined due to extremely limited French from a long time ago) a quick scan has not thrown up a BEM or acoustics code.
On the other hand, apart from dynamic FEM (solving exactly what I have not yet determined due to extremely limited French from a long time ago) a quick scan has not thrown up a BEM or acoustics code.
how might one model a Karlson-coupler in hopes to proportion so it may play reasonably smooth other than guesstimates from 3rd Z peak (assuming its partly coupled cavity) plus guesstimates based upon experience with other k-coupler?
An externally hosted image should be here but it was not working when we last tested it.
Tested CAE Linux.
Propably you could do all kind of things with this free distribution but just can´t in practice. It is very complicated because some of programs are in English and some only in French and all have a lot of properties you must understand and set. Really... Not meant for even average engineer
Learning takes a lot of time. Especially with this kind of SW.
On the other hand... If you know how to use this beast it would really be a super tool for it´s price... which is zero.
Propably you could do all kind of things with this free distribution but just can´t in practice. It is very complicated because some of programs are in English and some only in French and all have a lot of properties you must understand and set. Really... Not meant for even average engineer
Learning takes a lot of time. Especially with this kind of SW.
On the other hand... If you know how to use this beast it would really be a super tool for it´s price... which is zero.
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