The performance of a product is often only considered in terms of STC results from acoustic lab testing. Sound transfer that spreads throughout a structure cannot be properly tested in an acoustics lab. If the material or structure has low damping, the sound vibrations can travel from material to material for considerable distances, e.g. transferring into a wall, then to the ceiling and the floor above. If a structure has high damping, then the vibration dissipates quickly and cannot travel throughout the structure with ease.
Because of this, damping products like Green Glue Compound are vastly more crucial than lab tests show. Even in high STC assemblies, the Green Glue Compound will have considerable value in reducing the strength of the vibrations that do pass through the assembly from being able to travel throughout the structure with ease.