How does STC differ from other sound rating metrics like NRC or OITC? | ASLONG Guide

How Does STC Differ from Other Sound Rating Metrics Like NRC or OITC?

What is STC and What Does It Measure?

STC, or Sound Transmission Class, is a single-number rating used to measure how well walls, doors, windows, and other barriers block airborne sound. Primarily utilized for partition elements within buildings, STC focuses on mid-frequency sounds such as human speech. It does not account for low-frequency noises like heavy traffic or construction.

How is NRC Different from STC?

NRC stands for Noise Reduction Coefficient and measures the ability of a material to absorb sound rather than block it. While STC evaluates sound insulation, NRC rates materials like panels and ceilings for reducing echo and reverberation inside a room. NRC values range from 0 (no absorption) to 1 (total absorption).

What About OITC – How Does It Compare to STC?

OITC, or Outdoor-Indoor Transmission Class, is designed to assess a barrier's effectiveness at blocking exterior low-frequency sounds, such as traffic and airport noise, from entering buildings. Unlike STC, OITC is more relevant for exterior building elements and better reflects real-world, low-frequency insulation performance.

When Should You Use STC, NRC, or OITC Ratings?

Use STC ratings when comparing walls, floors, and doors for interior noise control. Choose NRC when your goal is to manage internal room acoustics by reducing echo. OITC is essential for doors, windows, and exterior walls exposed to significant environmental noise.

Why Are These Ratings Important for the Sound Insulation Materials Industry?

Understanding these ratings helps professionals select the correct sound insulation products for their specific needs. Using the right metric—STC for indoor noise, NRC for absorption, and OITC for external noise—ensures optimal performance and satisfaction for end users.