I am looking into making some subwoofers using td18h with passive radiators. Volume of the boxes will be as large as I can do, but most likely something like 220-260l. I want to do tuning to 20-21hz(yes, will most probably need some EQ). How many and what weight will I need for the passive radiators?
A vented port of decent size will be very long and take a lot of space inside the box.