Jim Ittenbach's Adventures in Soundproofing
A thick 12X9 carpet remnant was
purchased to hang up over a framed wall in an attempt to lower the amount
of noise from the heater/AC unit. It was also used to attempt to lower
the amount of noise traveling through the rest of the house. Although this did reduce the amount of noise from the HVAC
system it did almost nothing to reduce noise transmitted
through the rest of the house. This was intended to be an
initial phase, so research
was the next step. There was no shortage on the Internet, but most sites with anything remotely resembling
useful information had the ulterior motive of selling you soundproofing products. One concept that held
true in all the sites visited during the research is that the only way to soundproof a room is to build a room
inside the room and make sure it is completely isolated from the other parts of the existing structure.
Buy the book. It will save
you a lot of money.