Quote Originally Posted by dash View Post
With ductboard you just cut and fit on the job,very esay for them.The other reson to use the vanes is to have the airflow evenly,as directed by the vanes,thru the filter.3 to 4 feet of stright would do the same,but not possible.

If you follow your plan,ductboard is easier then metal to fab.
OK, ductboard is easier, but I have that center 2x4 at the front. Each
square measures 11"x12" opening size. Might be a bit iffy.

Just for kicks I threw down an old bath rug on the cavity floor, and a
12" x 18" USPS shipping box fit perfectly up at the front of the rectangle.
Right there that cut the sound by at least 15%.
I do plan on using some type of sound absorbing board and line the rest
the walls in there.

First I wanna see why I'm getting such a back flow
of air pushing down from the filter. Shouldn't a return intake draw in air only???
I'm calling the installer back. Maybe the blower motor could be turned down a tad, if that's even possible.
Some things need fixing on this install. I'm can feel a few minor cold air leaks at some areas at the evaporator, and there's a stream of air coming down at the plenum where it enters the attic.