Havent personally used a silencer but if your goal is simply to quiet down your fan noise a bit you can build a sound proof box for your fan to sit in. This has always been how i quiet down mine, i've used cardboard boxes, plastic totes, wooden boxes, etc for the housing, just has to be big enough to allow foam packing on all sides of the fan, then simply cut holes for your ducting and power cord to run through, then with the fan placed inside connect your ducting and proceed to fill the box with foam pieces, you can use pretty much any foam for this, the more dense it is the better though, ive used packing peanuts, cut up mattress topper foam, and actual sound proofing foam, all work but the sound proof specific stuff is a little better than the mattress topper was, and mattress topper was alot better than packing peanuts. once the box is closed up you will notice significantly less sound, hope this helps.
