Given the depth of the question, I would propose that you choose your best sound attenuator by simply pick up any sound attenuator catalogue (or an old phone book), close your eyes, flick pages until you randomly stop.
The page where you stop is your solution.
Here you go.
That company advertises sound attenuators/silencers along with many HVAC components. I was going to suggest removing this Thread, but why not leave it as a pothole in the road so others can go around it?
