From another thread (hope you don't mind Bryan, I copied and pasted your last message from the AS-EQ1 thread).
Quote:
The problem is that while the flex or duct board is great at not passing vibrations and absorbing mids and highs, it has almost no mass to it so it's effectively a hole for bass to pass through.
Yes - you want bends and length but you want those to occur starting where it enters your room 'aquarium' and goes for at least 15' with at least 3 90 degree bends in it before leaving the MDF box (the mass).
Think of it this way... If you cut a hole in the ceiling that you just spent a ton of time sealing up and getting sound proofed, and then just put 1/4" thick insulation in the flex or the 3/4" duct board, you effectively have a hole in your ceiling for bass to pass straight up to and through the subfloor above you.
I don't mind answering the questions at all. In all fairness to the purpose of this thread, we should probably continue it somewhere else.
Bryan
End Quote
Curious on more of this Bryan (thanks so much for all your incredible advice so far!!! :bigsmile

.
So, would building box at the exit of the vent (register of the HVAC into the HT), out of 3/4" MDF, let's say 3' x 3' x 3' with 1' of insulation on all sides of the interior and the ducting at 90 deg from the register take care of 'bass' transfer? Or would this create some type of transmission line at a specific freq in the lower regions?
Thanks!
Ray