Hi, this is Ken,and I will hopefully be able to solve your problem, since I majored in audio engineering.
There are different techniques used for different purposes, for example music studios, annoying neighbors and busy streets, etc., and also for the type of construction.
Please tell me:
(1) The dimensions of the room, including ceiling height (without a dropped ceiling).
(2) Is the room a perfect rectangle with parallel walls?
(3) Wood/sheetrock construction?
(4) How many windows and doors, and their sizes?
(4) what is the source or the sound you are trying to squelch?
(5) In your own words, what are you trying to accomplish? Please be specific.
When I receive your reply, I will be able to help you.
p.s. It is late now, so please expect a reply tomorrow.