Fans speed controller is what you need. You should be able to get that sound down to very reasonable. You can build a muffler out of a simple cardboard box. Do a search for DIY duct muffler and you'll be set.
bigsby Reviewed by bigsby on . Vortex fan too loud Hello people, I have a question for you. Anyone have any suggestions for muffling the roar of a 6" vortex fan? Mofo sounds like a jet engine! :) Thanks in advance for any help. Rating: 5