WinISD is freeware speaker designing software for Windows environment. You can design Closed, Vented and Bandpass boxes with this program. It also allows you to calculate few different types of filters.
NOTE! WinISD is still in betaversion, so please be patient with errors that may occur. Most helpfull would be if you would report them to Juha Hartikainen.
Old versions are also available:
If you like the software, please consider making a donation.