While some improvement in sound dampening is gained, this is the least effective of our three recommended solutions.
The subfloor above is left untreated, and the drywall on the ceiling below is completely coupled to the joists. Adding more drywall and Green Glue only provides modest gains.
Two extra layers of 5/8" drywall + two Green Glue damping layers on the existing ceiling
This solution adds an additional TWO layers of standard 5/8” drywall to the existing drywall or plaster ceiling. This makes the ceiling more massive (an additional 8 pounds per square foot) and again utilizes standard $12 drywall.
Install a medium coverage of Green Glue between layers. This will damp more vibration than a single layer of Green Glue, but still not all, since the vibration will still race through the framing (joists) above the new drywall layers, with some of this energy available to enter your ceiling and walls.