Home made duct muffler anyone?

looking to make a home made duct muffler anyone got any info?

yeah goto home depot and pickup a section of the rigid 4' long air ducting thats 2" larger than your ducting and get two reducers to go from the larger size down to your duct size. Glue acoustic foam to the interior of the duct and assemble, put the reducers on, and slap it inline with your duct...whala you have yourself a duct silencer

6" round duct
2 6" to 4" reducers
Egg crate foam (pricey)
Foil tape
Cut foam to fit inside 6" pipe add reducer to each end and tape connect to outlet of fan. This is for a 4" setup.

sweet thank man