reducer placement

I am setting up a 6" booster fan connected to a 4" carbon filter. The filter has to be upright to work so I will need to use a 90 degree connector (inline fan will be horizontal.

so my options are:

fan -> 6"-4" reducer -> 4" 90 degree conector -> filter

fan -> 6" 90 degree connector -> 6"-4" reducer -> filter

which would work best?

I am using the zen DIY pencil cup filter.


Thanks guys.

I would use the 6" 90, then reduce to 4". My logic being, if you have to use a 90 deg connector, keep the diameter as large as possible for less restriction.

yah thats what I was thinking.