How Can I Soundproof My Existing Ceiling?
Updated
You can soundproof an existing ceiling without demolition by sealing it and adding mass: caulk the perimeter, box in the recessed lights, and screw a second layer of 5/8 in. drywall (2.2 lb/sq ft, USG (opens in a new tab)) through into the joists. That helps with airborne noise like voices and TV, not footsteps, and the gain is modest: a second 5/8 in. layer added 3 STC points to an insulated 2x4 wall in USG's lab tests (opens in a new tab).
Sealing matters just as much as the new layer. In PABCO's Sound Design Guide (opens in a new tab), one unsealed 1/8 in. gap 1 ft long drops a partition from STC 46 to 36, and PABCO calls recessed lights "large open holes in the ceiling."
Watch out: Furring strips won't fix footsteps. Weyerhaeuser (opens in a new tab) says drywall on wood or stiff metal furring gives no significant improvement, because it's still rigidly tied to the joists.
For footsteps, the old drywall has to come down so the new ceiling can hang on resilient channel, with insulation in the joist bays. Weyerhaeuser credits resilient channel by itself with about 10 points of both STC and IIC. If you're between apartments, check with the building first, since the ceiling may be part of a fire-rated assembly.
How to soundproof a ceiling cheaply starts with the cheapest fixes. Panels on the old ceiling only cut echo, as do soundproof panels work on ceilings explains. You'll find echo options in the soundproof ceiling panels guide, with more in the soundproof panels guide and soundproof panels FAQ.