You can also make this with a box fan, construct a box with 4 filters of roughly the same size as the fan, the bottom of the box can be cardboard. Did this back

You can also make this with a box fan, construct a box with 4 filters of roughly the same size as the fan, the bottom of the box can be cardboard. Did this back in 2019 and it works great, though I ended up switching to a Coway a few years later because of the noise.