Use Green Glue noise-proofing Compound to make walls free of vibration. One tube of 828 ml is good for 1.5 square metres.
Seal cracks and holes in your sound-proof room with Green Glue noise-proofing Sealant.
The Green Glue Appgun is a must if you use Green Glue noise-proofing compound or sealant tubes, which do not fit in standard glue guns.