The single most cost-effective thing I did was replace the garbage hollow-core interior doors with nice hefty solid-core doors. Hollow-core doors are common for interiors since they&#x27;re cheap -- but they also act effectively as sound amplifiers since they&#x27;re just two vibrating planks with a small air gap.<p>Solid-core doors -- even ones filled with dense fiberboard (vs pure solid wood) are VERY effective at reducing sound. And they&#x27;re cheap -- you can get a nice basic one for ~$100.  If you pad the door frame with $5 in closed-cell weatherstripping and put in a $10 door sweep at the bottom (creating a nice seal around the door), you&#x27;ve eliminated one of the lowest-hanging fruits of sound transmission for very little $.<p>Next on the list:  Green Glue. If you don&#x27;t mind a bit of messy DIY stuff, you can make your own drywall&#x2F;Green Glue sandwich for a very reasonable amount of $.<p>Doors &amp; Walls cover about 80% of sound issues, and it doesn&#x27;t have to be expensive.