Numerical Simulation Software for Designing Loudspeakers?

[andy19191]

If one were to design, say, a folded horn or a transmission line cabinet is there any numerical simulation software available to help with the development?

[joensd]

Don´t know what you mean with numerical as it´s all bout numbers and stuff.
Anyway here are some :
http://www.aj-systems.de/indexe.htm
(very good program)
http://www.akabak.de/Ak-English.htm
http://www.quarter-wave.com/
http://www.users.bigpond.com/dmcbean/

greets

[andy19191]

Jens, thanks for the pointers but the programs use "lumped element" 1D modelling. Such simulations are very fast but rely heavily on empirical data and cannot really examine the 3D acoustic performance of the internal details of a cabinet. For example, the penalty in terms of reflections of folding a horn this way or that. My interest was in simulation programs which require a computational grid (hence numerical simulation) for the cabinet and take minutes or hours to perform a simulation.

[joensd]

Did you check the Ansys homepage?
http://www.ansys.com/products/multiphysics.asp
If Martin King doesn´t drop by you should send him your problem via email.

greets

[andy19191]

Yes I have some familiarity with Ansys software but I would assume it is far too expensive for someone designing loudspeakers for a hobby (also, I am fairly sure their software does not solve the required acoustic equations but there are Ansys-type engineering companies that sell the appropriate software but, unfortunately, for a similar price).

I think my original question may need clarifying. My enquiry is about software for simulating the sound waves in and around loudspeaker cabinents and whether DIY audio enthusiasts use such software. I do not have a particular design problem to solve. The question was prompted by looking at a few DIY audio designs that look a bit odd acoustically and knowing that a current PC is quick enough given a little patience to solve for the sound field in and around a loudspeaker cabinet (subject to one or two limitations).

[kelticwizard]

As I recall, Martin J. King's programs, using MathCAD, do not use lumped parameters, but instead actually crunch the numbers.

I have a slower computer, (300 MHz), and it takes a couple of minutes for any particular simulation to be calculated and graphed usisng MJK's software. Something must be going on there. All the lumped parameter programs graph it simultaneously.

[andy19191]

kelticwizard: I have very briefly scanned Martins equations. As you say, they are not based on lumped parameters but a 1D wave equation with a variable area. This is a step in the direction I was enquiring about but 1D cannot represent the 3D effects of folds, bends, the driver chamber, external cabinet effects, etc...

[joensd]

1D cannot represent the 3D effects of folds, bends, the driver chamber, external cabinet effects, etc..

Considering the precision of AJ-Horn and Martins sheets I´d like to ask what you think you´re aiming at further improving simulation results.
Quite a few measurements I´ve seen that were absolutely congruent with the simulations. If not, well I guess it´s other factors but mostly not the simulation that is the reason for the tolerance like materials used or several measurement flaws, wrong input data...

If you want to rebuild something like the nautilus from B&W such a "3D-program" will be quite useful of course.

greets

[andy19191]

> Considering the precision of AJ-Horn and Martins sheets I´d like to ask what you
> think you´re aiming at further improving simulation results.

joensd: At the moment I am not aiming at anything just asking questions about what is typcially used by DIY audio enthusiasts. Nonetheless, it is surely reasonable to expect simulation methods to improve as home computers become more able to run scientific/engineering software? (subject to the latter being available hence the question).

> Quite a few measurements I´ve seen that were absolutely congruent with the
> simulations. If not, well I guess it´s other factors but mostly not the simulation
> that is the reason for the tolerance like materials used or several measurement
> flaws, wrong input data...

I can only agree with you about the reasons for discrepencies between simulation and measurements but I am fairly sure you are not correct in believing simulations are good enough. The ear is certainly sensitive to significant to deviations in gross parameters like frequency response but it also picks up on many other lesser effects like harmonic distortion and secondary sources from edges, cabinet panels and internal cabinet reflections. Are current simulation methods providing useful information about such effects?

[MJK]

Interesting discussion!

My worksheets do use the 1D wave equation so they are better then a lumped parameter model, in my opinion, but are not as accurate as a complete 3D solution. I have used ANSYS to calculate the standing waves in TL enclosures to try an assess at what frequency the 1D wave equation results become inaccurate and to verify the fundamental tuning frequency of the enclosure. For a TL the inaccuracy seems to become apparent up in the 500 Hz or greater frequency range depending on the size of the line being modeled. For the bass range the 1D solution does OK even when folds are used to fit a long line to a rectangular enclosure. The ANSYS frequencies and mode shapes correlate well with the MathCad model below about 500 Hz. I have not used ANSYS for any more complicated acoustics problems although I believe the potential is there to do some more types of modeling.

I have a pair of MathCad worksheets that do calculate a 3D solution to the wave equation for rectangular closed and ported boxes. Right now they do calculate results but I need to clean up a few math errors to get accurate SPL plots. The results look interesting and promising, I would need to extend them to try and simulate folds and bends. These have been on the back burner for probably a year while I work on other improvements to the worksheets.

For me the biggest source of inaccuracy in the SPL predictions comes outside of the enclosure. The current worksheets treat the driver and open end as coincident sources radiating into 2 pi space. My newest worksheets are intended to calculate the SPL including the effects of driver and mouth/terminus/port position on the front or back baffle, baffle step, floor reflection, and even back wall reflection. I am still putting the finishing touches on these worksheets and I believe they will provide a better tool to assess BSC circuits and what you will hear in the way of SPL balance.

But in the end, listening is still the ultimate test.