How is STC measured and what does it indicate? | ASLONG Guide

How is STC Measured and What Does It Indicate?

What is STC and Why is it Important?

STC (Sound Transmission Class) is a numerical rating that measures how well a building material or assembly reduces airborne sound transmission. It is crucial in the sound insulation materials industry as it helps professionals, architects, and building owners select the right materials for noise control and optimize acoustic comfort in residential, commercial, and industrial spaces.

How is STC Measured?

STC is measured using standardized laboratory tests. Panels, walls, doors, or windows are placed in a specially designed test facility with two rooms separated by the test material. A calibrated speaker emits sound on one side, and sensors measure the sound that passes through to the other side. The difference in decibels across a range of frequencies (125 Hz to 4000 Hz) is calculated, and the results are plotted to determine the STC rating according to ASTM E90 and E413 standards.

What Does an STC Rating Indicate?

An STC rating indicates how effectively a material or assembly blocks airborne sound. A higher STC value means better sound insulation. For example, a wall with an STC of 30 provides only basic speech privacy, while an STC of 60 or more is required for spaces needing high levels of noise control, such as recording studios or theaters.

What Materials Have the Highest STC Ratings?

Dense, multi-layered constructions—such as concrete walls, double or triple-glazed windows, and specialized acoustic panels—typically have the highest STC ratings. Adding mass, using resilient channels, installing insulation batts, and minimizing gaps or penetrations can significantly increase a wall or partition’s STC value.

How Can STC Ratings Help in Material Selection and Building Design?

STC ratings guide professionals in choosing appropriate materials for specific environments. For example, residential bedrooms and offices may require walls with an STC of 40–50, while areas with stricter requirements—like hotel rooms near busy streets—benefit from higher STC-rated materials. Understanding these ratings ensures compliance with regulations and boosts occupant satisfaction.