Understanding STC and OITC: The Definitive Guide to Acoustic Ratings

What are STC and OITC? STC (Sound Transmission Class) is an integer rating that determines how well a building partition attenuates airborne interior sound, while OITC (Outside-Inside Transmission Class) measures the isolation of low-frequency exterior noise like traffic. When designing commercial spaces, recording studios, or high-end residential properties, controlling noise requires understanding these specific acoustic metrics.

STC (Sound Transmission Class) Explained

STC evaluates interior walls, ceilings, floors, doors, and interior windows. The higher the STC rating, the better the sound isolation. According to standard acoustic engineering benchmarks:

• STC 30-35: Loud speech can be heard and understood.
• STC 40-45: Loud speech can be heard but not understood; normal speech is inaudible.
• STC 50+: Very loud sounds (like musical instruments or shouting) are barely audible, reducing ambient noise by over 45 dB. This is the gold standard for premium acoustic environments.

OITC (Outside-Inside Transmission Class) Explained

While STC is excellent for interior noise, it falls short when measuring low-frequency exterior noise such as transportation infrastructure or aircraft. OITC places more emphasis on low-frequency sounds (down to 80 Hz), making it the superior metric for exterior windows and facade elements.

Choosing the Right Acoustic System

At Kiran Slido Craft, our acoustic engineering focuses on both high STC and OITC performance. Our premium soundproof sliding doors and casement windows utilize advanced compression seals, specialized Polyvinyl Butyral (PVB) acoustic laminated glass, and decoupled aluminum frame structures. These engineered systems consistently achieve STC ratings upwards of 50+, ensuring total acoustic isolation regardless of the external environment.