Understanding STC – STC is roughly the decibel reduction in noise a material/partition can provide, abbreviated ‘dB’. The human ear perceives a 10dB reduction in sound as roughly reducing the volume by half. For example, a sound reduction from 50dB to 40dB seems half as loud. This is an important fact to keep in mind when considering a sound solution that ‘fits’ the problem. To understand how to soundproof a wall to create a higher STC rating.
Example: For instance, sound insulation material with a 35 STC would block most normal speech while material with a rating of 60 would render most sounds inaudible.
Common STC Ratings
A common acoustic issue in virtually any space is sound transmission. Sound transmission can be both airborne and/or structure borne vibration.
Airborne sound travels through the air and can transmit through a material, assembly or partition. Sound can also pass under doorways, through ventilation, over, under, around, and through obstructions. When sound reaches a room where it is unwanted, it becomes noise. Noise such as that from automobiles, trains and airplanes can transmit through the exterior structure of a building. In the same way, noise from mechanical equipment or speech can transmit from one room within a building to an adjacent space.
Sound transmission can cause noise control, confidentiality, and privacy issues. Sound from a noisy environment such as a mechanical equipment room or an area with loud activities or music can transmit through a partition into a quieter space. This will cause unwanted noise within the quieter space. This is not only an annoyance; in several cases it can cause the quieter space to become unusable for its intended purpose. Several spaces require confidentiality. Offices of counselors, lawyers, or human resource departments cannot function in a space where sound will transmit through the surrounding walls and into an adjacent space. In most other office situations if confidentiality is not an issue, privacy is. If sound transmission is not properly controlled, the space or environment will not provide privacy for its users.
- When soundproofing rooms, the STC of your doors & windows need to be equal to or greater
than the STC of your walls in order to maximize the rating.
- Structurally decoupling drywall panels from each other (using steel studs, a staggered-stud wall, double wall stud, or resilient channels) can produce an STC rating as high as 63 (for a double stud wall) and will result in effective low-frequency loss. This figure, when compared to a normal wall with an STC of 33, will make most frequencies inaudible, making the room sound 88 percent quieter.
- Music-related sounds may require the highest STC ratings. In practical terms, a 55 STC rating will prevent a resident living in a multi-family home from being bothered at all by their neighbor’s loud music.