i am adding transfer ducts w/1 inch soundlining over full height partitions ,most are only 12 inches long .whats the s/l doing for me ,,i've been showing this way for yrs and never thought about it
If its strictly to connect one plenum ceiling to another, I would say that the lining is doing nothing. If it's hard ducted from a return grille in one occupied space to another, then I could see the benefit. If it's just drywall partition with no insualtion, you are probably transferring more sound through the wall anyway.
Typically I would make a transfer duct out of an elbow or a 'Z', not a straight piece. The lining will absorb high frequency noise (e.g. talking). One other piece of advice is to watch where the return grilles are, if they are just on the other side of the wall from each other with a transfer above them you can clearly hear between rooms.