What is the most cost-effective way to sound-proof a room?

Question by Bill Smith: What is the most cost-effective way to sound-proof a room?
In the process of building interior walls to create offices inside a building. Private conversations will be taking place in those offices, so they need to be soundproofed. Is there any particular (preferably inexpensive) material that can be placed within the walls that is effective at blocking sound?

Best answer:

Answer by Phil
The best way to soundproof a room is to build double walls around the office. both walls should have batts of insulation in them and leave a small space between the walls so that vibrations cannot pass from 1 wall to the other. It is also good to put a foam sill seal material under and over the framing to lessen the vibration transfer into the main building structure.

Give your answer to this question below!