There is a fair amount of general open source simulation code that can be used to solve loudspeaker related problems. What physical processes do you want to simulate? Note that little of it will be easy to use interactive GUI programs with most being batch programs controlled by scripts and text files. There will be little in the way of user's guides and fairly often what is available won't be in English.
Without knowing what you want to do it is hard to answer. If a low order linear acoustic BEM code is a good choice for what you want to simulate then acousto has been a better choice for some since it is free open source not commercial proprietary closed, will run on linux/OSX as well as Windows, integrates with widely used input and output processing software, runs in parallel, etc... There is other software like elmer and alternative numerical approaches to BEM for solving acoustic wave problems with their pros and cons. Without details of the information required and constraints like user capabilities, OS, memory, number of processors, etc... one cannot really say.
in AKABAC you can model your cabinet or horn that you mock up in 3d fusion or Autocad or similar..... I'd like to see what else software can do this like AKabak, thoughts were it might gel with me better...might in AKABAC using 3d models it will sim polar response and such.
VituixCad is in use currently but it cannot model a horn.
VituixCad is in use currently but it cannot model a horn.