I just found the best calculator program ever if you build boxes or will one day. I think its only for ti 83/84 plus though.
Its a Box Calculator program..It lets you figure out Port Length,Frequency,Volume,Slot Disp.,Round Disp.
Heres a link, but your gonna need the TI conncect software/cable. I bought mine off ebay you need it to download things like games and stuff.