What is S.T.C.?

STC
Sound Transmission Class is a single-number system used to rate the airborne sound transmission performance of a wall, panel, ceiling, etc. The higher the STC number, the better the product's ability to block sound transmission.

Drywall Construction
Drywall construction can achieve higher STC ratings, but the costs are much higher. For instance, if you wanted to achieve a STC of 45 or greater, the minimum construction for such a wall would be one layer of 1/2" gypsum board on one side and two layers on the other, attaching to metal studs and packed with fiberglass insulation to fill the space between the gypsum sheets. Additionally, you would need to bring the drywall construction to the slab above through the ceiling tile and not cutting in for electrical or data outlets. (Goldbond Design U498, WP-545, WP 7079, ASW 1215, Test no. 2617.)

A 4"-wide typical drywall construction consists of one layer of 5/8" gypsum board on each side of the metal studs with no insulation in between. This type of construction will have an estimated STC of 36. You can upgrade the STC value of this wall construction to 42 by adding insulation and not cutting in for electrical and data outlets. (Goldbond Design no. U499, WP-755, WP 6905. Test no. 2542.)