Usually thick insulation because you need mass to block bass. Like rockwool: https://www.rockwool.com/north-america/products-and-applications/products/safensou

Usually thick insulation because you need mass to block bass. Like rockwool: https://www.rockwool.com/north-america/products-and-applications/products/safensound/?selectedCat=safensound®%20downloads https://www.rockwool.com/north-america/products-and-applicat...