> why use multiple 1" thick filters to build a box, when you could just use 1x 4" filter. Probably uncertainty over how effective fans are when immediately obs

> why use multiple 1" thick filters to build a box, when you could just use 1x 4" filter. Probably uncertainty over how effective fans are when immediately obstructed, and maybe concerns about particles possibly getting deflected backwards if a filter messes with a smooth, laminar flow. This is, if we think of two kinds of airflow: 1. [laminar flow](https://en.wikipedia.org/wiki/Laminar_flow https://en.wikipedia.org/wiki/Laminar_flow ), which is like a smoothly flowing river; 2. [turbulent flow](https://en.wikipedia.org/wiki/Turbulence https://en.wikipedia.org/wiki/Turbulence ), which is like erratic flow inside a mixer; then it seems like a box-fan might effect a laminar-flow further away from the blades (under normal circumstances), but could it be more turbulent near the blades? The boxed-in design seems to try to dodge assumptions about how air flows near the blades, reducing uncertainty about how turbulent-flows might screw with it.