[quercusa]

If you go the old school "filter taped to box fan" route, be sure to add a shroud for the corners, as blade tip turbulence there actually causes reverse air flow. See the article by the 'R' of Corsi-Rosenthal.

https://www.texairfilters.com/how-to-improve-the-efficiency-...

[burnt-resistor]

I bet this moves more air per unit noise and/or power too.