Interior Design Implementation (IDIX) 2 Practice Exam 2026 - Free Interior Design Practice Questions and Study Guide

Sound isolation between interior rooms is quantified with the STC rating, which stands for Sound Transmission Class. This measures how well a wall or partition blocks airborne noise from passing from one room to another. The test evaluates transmission loss across a range of frequencies, and a higher STC means better isolation of speech and other ordinary sounds between spaces.

Other terms play different roles: IIC (Impact Isolation Class) gauges how well a floor-ceiling assembly blocks impact sounds like footsteps, not airborne noise between rooms. NRC (Noise Reduction Coefficient) describes how much sound a material absorbs inside a room, affecting reverberation and interior acoustics rather than transmission between rooms. SAB isn’t a standard, widely used metric for wall isolation. Therefore, the term that specifically measures sound isolation between rooms via transmitted airborne sound is STC.