Acoustics
The disturbance of molecules in an elastic medium (usually air).
Decibels (dB)
A logarithmic unit used to measure the intensity or loudness of sound.
Hertz (Hz)
Measure of frequency (beats per second).
Frequency
Beats per second; low frequency = long wavelength. Measured in Hertz
Octave Bands
Groupings of frequencies on a geometric scale used in architecture.
Sound Absorption
Sound entering a material and becoming heat by causing friction.
Absorption Coefficient
Ranges from 0 (full reflection) to 1 (fully absorbed).
Noise Reduction Coefficient (NRC)
The average absorption coefficient across four mid-frequency octave bands.
Scattering
Sounds won’t scatter on geometry smaller than their wavelengths.
Reverberation Time (T60)
The time it takes for sound to drop 60 decibels.
Necessary properties for a sound barrier (3)
Airtight, Massive, Structurally Discontinuous
Sound Transmission Class (STC)
A rating trying to illustrate performance across all frequencies for blocking sound. A higher STC rating indicates better sound insulation. Minimum 50 required between MF units
Noise Criteria (NC)
Single-number rating specifying the max allowable continuous background noise (Higher = louder)
dBA
A-Weighted Decibels that summarize sounds across frequency level based on human ear sensitivity.
Impact Insulation Class (IIC)
a standardized, single-number rating that measures a floor-ceiling assembly’s ability to block impact-generated structure-borne noise, such as footsteps, dropped objects, and moving furniture. Higher numbers indicate better sound isolation, with a minimum of IIC 50 usually required by building codes for multi-family dwellings
Sound transmission of Concrete and Wood at different frequencies
Concrete is worse than wood at high frequencies, wood worse than concrete at low frequencies.
Sabins
The unit of total sound absorption in a room (SF x Absorption Coefficient).
Inverse Square Law (Acoustics)
Sound intensity decreases by 6 dB for every doubling of distance.
Mass Law (Acoustics)
Doubling the mass of a partition increases Transmission Loss by roughly 6 dB.
Resilient Channels (Acoustics)
Metal rails used to mechanically decouple drywall from studs to improve STC.
Diffusion (Acoustics)
The scattering of sound energy evenly in a space using irregular surfaces.
Echo
A distinct reflection of sound that arrives more than 50ms after the direct sound.
Flutter Echo
Rapid, repetitive reflections between two parallel, highly reflective surfaces.
