Two Numbers, Two Kinds of Noise, One Assembly
STC (Sound Transmission Class) is airborne sound: voices, televisions, music. The defense is mass. Pouring 1.5 inches of gypsum concrete over a bare wood subfloor adds the mass the assembly needs. Higher STC means less of the neighbor’s television.
IIC (Impact Insulation Class) is structure-borne sound: footfalls, dropped objects, dragged chairs. Mass alone will not stop it. The defense is decoupling, and that is the acoustic mat’s job: the gypsum topping floats on the mat, so impact energy is absorbed instead of transmitted to the ceiling below. Higher IIC means fewer footsteps overhead.
One thing worth knowing: STC and IIC lab ratings describe a whole tested assembly. Change any layer and the rating no longer applies, which is why the mat product, topping thickness, and topping density in your spec are not suggestions. We install the mat and pour the topping as one scope, and the Smart Batch® GC-1 weighs every batch against the mix design the assembly was engineered around, then archives the record to the cloud for your closeout file.
Systems We Install
- Acoustic mat + gypsum concrete topping: the standard wood-frame multifamily assembly; sound attenuation mats (including Formulated Materials M-series and comparable systems) under Treadstone® gypsum toppings
- Sound mat under resilient finish floors: attenuation mats installed for sound-rating compliance where LVP, sheet vinyl, or engineered flooring is going down
- Retrofit sound upgrades: adding mass and decoupling over existing subfloors in renovation and change-of-use projects
- Assembly consultation at bid time: we read your architect’s tested-assembly callouts and flag mismatches before they become change orders
