I. Definition and Core Function of STC
STC (Sound Transmission Class) is a standardized indicator that measures the ability of a building material or structure to block airborne sound. Its value is calculated through laboratory testing of sound attenuation at different frequencies. Higher values indicate greater sound insulation performance. For example:
STC30: Blocks only light conversations and is suitable for locations with minimal sound insulation requirements (such as ordinary warehouses).
STC50: Effectively blocks normal conversations and television volume, meeting basic requirements for homes and offices.
STC60+: Almost completely blocks traffic noise and musical instruments and is commonly found in recording studios and high-end hotels.
II. STC Testing and Certification Process
Laboratory Testing: Samples are exposed to sound waves at multiple frequencies (125Hz-4000Hz) in a professional acoustic laboratory, and the difference in sound pressure levels is measured.
Key Certification Information: Taking Hong Kong STC certification as an example, the basic fee is approximately HK$30,000-80,000 (including testing and factory inspection). Expedited service can shorten the process to 15 working days.
Validity: Typically 5 years, with regular re-inspections required.
III. Comparison of STC Values for Common Materials and Structures
Single-layer gypsum board (12mm): STC values range from 28-32, suitable for temporary partitions and low-demand office areas
Double-layer gypsum board + rock wool (50mm): STC values range from 45-50, suitable for residential partition walls and conference rooms
240mm brick wall: STC values range from 48-52, suitable for schools and hospital wards
Double-layer insulated glass windows (6+12+6mm): STC values range from 35-40, suitable for street-facing residences and ordinary offices
Professional soundproofing walls (multi-layer composite structure): STC values range from 55-65, suitable for recording studios, theaters, and high-end hotels
IV. How to Apply the STC Index in Renovation
Residential: Bedroom partitions are recommended to have an STC of 50+, using a "double-layer gypsum board + soundproofing felt + stud construction."
Commercial spaces: Open-plan offices require an STC of 45+. Lightweight steel stud partitions filled with glass wool can be used to balance cost and performance. Special places: KTV boxes require STC60+, with professional soundproof doors (STC55).
Door and window upgrade: ordinary aluminum alloy windows (STC25) are replaced with double-layer hollow glass windows (STC35), the cost increases by about 30%, and the sound insulation increases by 40%.
Soft furnishing assistance: thick curtains (NRC0.5) + carpets (NRC0.3) can reduce 5-8dB noise.
Gap treatment: Use sealing strips to fill the gaps in the door frame to avoid the "sound bridge" effect that causes the STC value to drop by 10-15.
Daliachi | Scientific material selection, reconstructing the spatial sound environment with STC values
By accurately matching the STC level with scene requirements, a balance between sound insulation effect and cost can be achieved.
