The author fabricated a model to represent a wall whose other side is a neighbor’s property, where nothing can be changed.
The crew installs a "mass-loaded vinyl" (MLV) membrane over stud cavities filled with sound-blocking insulation such as Roxul rock wool or QuietInsul.
All seams, including the edges, are sealed with a special tape made from the same MLV material as the membrane.
Clips and channel are used for drywall furring. The clips are fastened to the studs with screws through plastic washers.
The screws touch the studs and the washers, but not the metal of the clips, effectively decoupling the studs from the clips.
Being careful not to damage existing plumbing and wiring, the crew tears out any spray foam insulation by hand and replaces it with special acoustic rock wool fiber batts.