ARCHITECTURAL
Surface treatments and room geometries dominate architectural acoustics. Project costs can skyrocket for specialty products that often exceed $20/sf and are sometimes easily replaced with cheaper and equally effective commodity products.
CONSIDERATIONS
SOUND TRANSMISSION CLASS (STC)
STC is a lab rating that describes the approximate decibel (dB) reduction in noise across a building assembly. Increasing STC is usually achieved by providing mass (drywall, CMU, etc) separated with an airspace (more is better). Isolated walls are often not required and completely sealing penetrations is usually more important. For example, a 1% sound leak (surface area) results in a 20dB transmission loss limit...in other words no privacy! This condition is very common - think about doors with no gaskets or piping penetrations that haven't been sealed.
ABSORB + BLOCK + COVER-UP (ABC)
ABC is a common acronym that describes three ways to improve the room acoustics of a space. Absorbing sound typically involves providing surface treatments with higher Noise Reduction Coefficients (NRC) on the ceilings, walls, and floor (thin carpet tile doesn't do much!). Block means not allowing direct line-of-sight, but this is not always possible in open office spaces. Cover-up is often achieved using sound masking, though this is not always an option in spaces such as conference rooms and most private offices.
SPEECH PRIVACY (SP)
Combining sound transmission class (STC) and background noise (NC) results in speech privacy (SP). SP describes how audible and intelligible a normal and raised voice (speaker phone, yelling, etc) is:
SP = STC + NC
SP typically ranges from 55 (no privacy) to 85 (total privacy). So for a typical conference room with STC-50 walls and NC-25 background noise:
SP = 50 + 25 = 75
