Sound Transmission Class (STC) Rating System
Sound Transmission Class is a rating of how well airborne sound can be attenuated by a building partition or building material. Sound transmission is a common acoustic issue in virtually any space. Sound can be transmitted both airborne and/or structure borne vibration. Airborne sound can almost travel through any openings in a house. Sound can pass through a material, assembly or partition, under doorways, through ventilation, over, under, around and through obstacles. Noise occurs when unwanted sound reaches a certain room in a place. Noise can be generated from automobiles, trains, airplanes, and human’s mouth and construction work in progress.
There are some issues that can be caused by sound transmission; they are noise control confidentiality and privacy issues. Sound can be transmitted from a noisy environment to a quieter space and it turns into unwanted noise. Apart from being a nuisance, unwanted noise in a quieter space can render that space unusable for its intended purpose.
The basis for determining Sound Transmission Class of a partition is by measuring Transmission Loss over a range of 16 different frequencies between 125-4000 Hz. Whereas, Transmission Loss is a measurement of the ability of a partition to block sound at a given frequency (dB) that is reduced when passing through the partition.
The general rules of thumb for controlling noise between spaces:
- To achieve optimal isolation, a wall must extend to the structural deck
- Sound will travel through the weakest structural elements (e.g. doors, windows, ventilation or electrical outlet)
- Doubling the mass barrier will increase STC rating by approximately 5 dB (i.e. clearly noticeable)
- Installation of sound insulator (e.g. glasswool, fibreglass) within a wall, floor cavity and ceiling cavity will increase STC rating by approximately 4-6 dB (i.e. clearly noticeable)
- Specialty insulations performs just as good as standard batt insulation
- Metal studs perform better than wood studs
- Increasing air gap within a wall cavity or window assembly will improve soundproofing quality
Changes in STC in Apparent Loudness:
Recommended STC ratings:
Generally, loud speech can easily be transmitted through an STC 30 wall. However, it will not be audible through an STC 60 wall. The common STC rating for a common building is STC 50 and this wall blocks approximately 50 dB sound transmissions. Hence, in order to satisfy the building code requirement, an STC 50 assembly is required.
Please Contact SCS for further inquiries regarding to the STC rating systems used for each window.