Eyrie Productions, Unlimited
There's variations with just 1 or 2 filters you can make too.https://cleanaircrew.org/boxfanfilterfaq/
--------Wedge Defense Force General Order 12: "Try to avoid freaking the mundanes."
Oh, there's commercial systems that do all of this. But between cost, panic purchasing, and limited need, it's sometimes the only option.
Peter Eng--Insert humorous comment here.
version 3.3 © 2001 Eyrie Productions, Unlimited Benjamin D. Hutchins E P U (Colour)