It is called a Cosri-Rosenthal box [1]. I've built three variations on these using different kinds and sizes of Filtrete filters they are very cheap and effect

It is called a Cosri-Rosenthal box [1]. I've built three variations on these using different kinds and sizes of Filtrete filters they are very cheap and effective. The downsides are that they take up a lot of space, are a big eye sore and awkward to carry and move. They also can make a lot of (white) noise on high, which can mask sounds you want to hear. They're great for special situations like wildfires or out of the way areas like basements where looks don't matter. For common living spaces we use Coway Airmega AP1512's which are relatively compact, auto cycle up and down fan speed and are much more attractive than DIY stuff. [1] https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box