Sound Transmission & Impact Isolation

Design Conditions

There are many building and program types which require sensitivity to sound. Some of these are obvious, like music venues and sound recording studios. Some are less obvious, but can severely alter a user's experience, such as hospitality and multi-family; sound transmission from a hallway to units or between units.

Regardless, always look to the program's specific needs to determine the conditions that need to be designed for. Special care should be noted for potentially extra or sensitive requirements if converting from one program use to another. A premium might need to be paid in order to make the space usable from a ‘sound’ perspective.

Sound Transmission vs Sound Absorption

Sound transmission is the amount of sound that makes it through a barrier; in other words, the amount of sound isolation. Sound absorption is the amount a material absorbs to stop reflecting the sound (reverberation) back into the space. If you have an echo in a room, you want to increase sound absorption. If you can hear your neighbors, you want to increase sound isolation.

Sound Transmission Class (STC)

Sound Transmission Class (STC): Average of a barrier’s ability to reduce sound over several frequency bands. Essentially, the higher the value, the better the barrier is at stopping sound, or in other words; the higher the value, the better the ability of the barrier to control sound transmission.

• STC Values are determined under ideal laboratory conditions. In reality, construction tolerances and quality of work should be taken into account, along with all the different types of openings in a barrier. For example, the STC rating of a wall does not matter much, if the construction of the wall does not exactly match those criterias; or the wall is perforated with many windows or openings.
• Walls and floors are generally rated with their STC Rating.
• Any openings in the barrier (doors, windows, MEP, etc) that have a lower STC rating than the barrier itself, will lower the overall rating of the barrier.