silencing exhaust fan

[D.W.FAAMER]

bought a new 424cfm inline exhaust fan. problem is that venting the 6 inch pipe out a wall through a 4 inch hole at the end sealed around hole creates turbulance,in other words it sounds like a 747 warming up for take-off when it's on medium(speed controller).on high i'd rival a shuttle lift off.what can i do? make hole full 6 inches cutting down resistance,and trying to conceal a 6 inch hole. or what? help fast.

 

[SPEARCHUCKER]

Can you put a beveled lip to the wall? So its running out smoother.
Maybe a couple inch thick piece of thin plastic or something across the middle. Going towards the inside. Splitting the airflow before it can cause 1 big turbulence mass.
Or reduce the line to 4 inch sooner than right at the wall.

 

[D.W.FAAMER]

u think reducing it sooner will kill some of the sound? i will wrap insulation around ducting tonight also see if that helps.dammmm.loud as hell hate that.