Jeff writes again from Syracuse, Indiana: "I'm insulating the floor between the basement and 1st floor. The floor joists are 2 X 12 and I plan on installing a suspended ceiling. Can you give me an idea of the STC difference between a suspended ceiling and a 1/2 drywall with resilient channel. The other question is what is the STC difference between going from 4" 6" 8" 10" of fiberglass in the floor joist."

Answer: STC (Sound Transmission Class) is an assembly rating. Insulation and other individual products do not carry STC ratings alone. In order to calculate the approximate STC, we would need to know the entire assembly including:
- Finish of the floor above.
- Is there underlayment and how thick?
- What thickness is the insulation?
- What are the 2 x 12s spaced at?

Owens Corning does not have information comparing general assemblies of the type you describe.