6" Muffler on a 4" fan

I just got myself a 4" Vortex fan, but I cant seem to find a 4" muffler to go with it (only 6" + at local hydro shop). There is a bunch online but they all cost 100$ + for just the shipping (im in Canada). Anyone know if I can put a 6" muffler on the 4" fan with a 6" to 4" duct reducer? Thanks

Yeah that will work. Any more serious questions you should just call the manufacturer.