These are the most effective ways to soundproof existing walls from my list. Add Insulation Install a Second Layer of Drywall With Green Glue Use Resilient Clips & Channels Add Mass Loaded Vinyl Build a New Wall in Front of Existing Install Acoustic Foam Panels

Installing an additional layer of acoustic drywall over an acoustic membrane between materials and closing all gaps with an acoustic sealant to block cracks and gaps in both new and existing walls is the most efficient noise reduction method but using resilient channels, applying blown-in insulation, or covering the entire wall with soundproof blankets and curtains are other common solutions known to reduce noise.

The best way to soundproof an interior wall is to add another layer of acoustic drywall with an acoustic membrane between the layers. Also, close any air gaps around fixtures with acoustic caulk.