Density + Disconnection
The key to the success of sound insulating a common wall or ceiling is to introduce a combination of density and disconnection to the assembly. Density impedes vibrations (like grabbing the prongs of a tuning fork to kill sound), while disconnection forces the collapse of the sound wave (like snipping a string pulled tight between two coffee cans). Luxury grade STC values in the 55-60 range, or greater can be triggered by adding these two components to your common surface.
Layering Outperforms Pre-Engineered
Pre-engineered drywall is one means by which density can be added to your surface, but there are more cost effective alternatives that will trigger equal or greater sound results. To trigger luxury grade STC values, the industry experts prefer to see a layering approach. Much like clothing that insulates against cold temperatures, layering to a common wall or ceiling assembly will do a better job of insulating against sound bleed than will a single medium like pre-engineered drywall.
The image shown here illustrates the use of a channel system backed by the density of mass loaded vinyl and fronted by standard 5/8" drywall. This technique exceeds the STC values typicallly triggered by pre-engineered drywall. The density is maintained with the black dB-Bloc layer, while the stripping system introduces a dead air pocket that better insulates the wall by forcing the collapse of the structural connection points. The finishing layer is standard drywall, offering a much more cost effective sound insulation approach. dB-Bloc is shipped to your job site in 54" x 30' rolls, and can be stapled into place.
Your Soundproof Drywall Alternative
Your better alternative is to separate the density from the drywall and introduce a new dead-air pocket. This is a layering approach that starts with the use of dB-Bloc. dB-Bloc is a thin, mass loaded vinyl membrane that deadens a wall's ability to vibrate, just like pre-engineered drywall does. Anchor dB-Bloc to your surface with a staple gun, then install a firring strip spacer, then your drywall. This procedure creates that dead-air pocket you need to for the collapse of the sound wave, and will still maintain the density you need to impede vibrations. Your advantage is twofold: you trigger a better result at a lower price.