Acoustic Terminology
Ambient Noise
The distinctive acoustical characteristics of a given space consisting of all noise sources audible at that location. In many cases, the term ambient is used to describe an existing or pre-project condition such as the setting in an environmental noise study.
Attenuation
The reduction of an acoustic signal.
A-Weighting
A frequency-response adjustment of a sound level meter that conditions the output signal to approximate human response.
Decibel (DB)
Fundamental unit of sound, A Bell is defined as the logarithm of the ratio of the sound pressure squared over the reference pressure squared. A Decibel is one-tenth of a Bell.
CNEL
Community Noise Equivalent Level. Defined as the 24-hour average noise level with noise occurring during evening hours (7.00pm-10.00pm) weighted by a factor of three and night time hours (10.00pm-7.00am) weighted by a factor of 10 prior to averaging.
Frequency
The measure of the rapidity of alterations of a periodic signal, expressed in cycles per second or hertz.
Ldn
Day / Night Average Sound Level. Similar to CNEL but with no evening weighting.
Leq
Equivalent or energy-averaged sound level.
Lmax
The highest root-mean-square (RMS) sound level measured over a given period of time.
Loudness
A subjective term for the sensation of the magnitude of sound.
Masking
The amount (or the process) by which the threshold of audibility for one sound is raised by the presence of another (masking) sound.
Noise
Unwanted sound.
Peak Noise
The level corresponding to the highest (not RMS) sound pressure measured over a given period of time. This term is often confused with the "Maximum" level, which is the highest RMS level.
Threshold Of Hearing
The lowest sound that can be perceived by the human auditory system, generally considered to be 0 dB for persons with perfect hearing.
Threshold Of Pain
Approximately 120 dB above the threshold of hearing.
