I recently stayed in an apartment that didnt have central air so I created a corsi-rosenthal box since the smoke from the Canadian wildfires were so bad.
After 30 days of continuous use, with very minimal periods of it being turned off, this is what the filters look like!
It's disgusting yet also so satisfying to see the filters get darker from debris, dust, and dirt.
Edit: typos
Pretty sure its about creating negative suction below the fan. Instead of just pulling air from the intake side of the fan, its pulling it from all 4 directions. Theoretically the air flow going through the filter would be at least 4x but probably more in practice.
Well the rate of airflow through the fan is at its maximum when there are no filters attached to it. Each filter likely slows down airflow if hooked up in a "series" pattern, but you're right that having these four in "parallel" will increase flow compared to one strapped directly to it. I'm sure there's a problem with reducing the airflow too much, because the fans motor would start to burn, and I'd guess that hoisting the fan up in the air rather than standing upright on the ground would improve airflow.
That being said, I'd need to do it myself and see what strapping a single filter to a fan does. I have hunch it wouldn't burn out the motor, and I imagine it'd still be effective. If the rate of airflow isn't severely reduced with a single filter, that'd just mean the same amount of air is being forced through a filter in either case (1 vs 4 filters).
Of course the single filter would wear out four times as fast so it probably won't make a difference in how many you buy in the long run. I'm just sort of rambling at this point but it's a neat concept to think about.