Cutoff frequency - The lowest frequency above which the normal incidence sound absorption coefficient is at least .990 for an anechoic wedge, or set of wedges,

Critical distance - The distance from a sound source at which the direct energy (energy radiated directly from the source) is equal to the reverberant energy (radiated from walls, floor and ceiling).

Constructive Interference - The addition of two waveforms of similar phase. Constructive interference is responsible for the production of standing Wavesin which a signal and its successive reflections are continually added to one another. The opposite is destructive interference.

Coloration - A term used to indicate audible alterations to sound due to its environment. Coloration can be a result of standing Wavesor room resonances

Cocktail Party Effect - The ability of a listener to focus attention on a single talker among a mixture of crowd conversations and background noise while, at the same time, ignoring speech from other locations. Understanding is possible due to the ear / brain discrimination of unwanted sound as well as lip reading and body langauge.

Comb filter - A distortion produced by combining an acoustical (or electrical) signal with a delayed replica of itself (offset in time). The result is constructive and destructive interference that results in peaks and nulls being introduced into the frequency response.

Ceiling Cloud - An acoustical panel suspended in a horizontal position from ceiling or roof structure.

Ceiling Attenuation Class (CAC) - Rates a ceiling's efficiency as a barrier to airborne sound transmission between adjacent closed offices. Shown as a minimum value, previously expressed as CSTC (Ceiling Sound Transmission Class). A single-figure rating derived from the normalized ceiling attenuation values.

Cancellation - The destructive interference of two or more sound waves. Waves of similar frequencies and amplitude, but of opposite phase (180°F) produce mutual cancellation effects.

Bright - Listening term that usually refers to excessive upper frequency (treble) energy.