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Insulation of Building Against Highway Noise

Glossary

Absorption	The dissipation of noise energy by viscous interaction at porous surfaces such as carpets or draperies.
Acoustic Baffle	A fitting in a ventilation duct that attenuates noise traveling along the duct while presenting little flow resistance.
Attenuation	A reduction in the noise level of transmitted noise, as often provided by a berm, wall, or acoustically-absorptive ground surface. The amount of attenuation is measured in dB.
Decibel	A unit for describing the amplitude or level of acoustical quantities - see Level. Decibel is abbreviated dB.
EWNR	Abbreviation for Exterior Wall Noise Rating, a single-number rating of the maximum attenuation of a particular type of exterior wall construction.
Histogram	A graph showing the frequency of occurrence of noise at various levels.
Infiltration	The leakage of air through wall panels due to incomplete sealing of corners, window frames, and doors.
L_eq	Abbreviation for Equivalent Noise Level, a metric for describing the noise level of a time period of fluctuating environmental noise with a single number. L_eq is an average level based on the average energy content of the noise rather than average noise pressure level. It is the constant noise level which would contain the same amount of acoustical energy as a fluctuating level for the given period. L_eq values are not measured directly, but are computed from measurements, often taken over 1, 8, or 24-hour periods. These measurements, and the resulting L_eq values, are usually A-weighted.
L_10´ L_50´ L₉₀	Statistical metrics indicating the noise level which is exceeded for a particular percentage of the time during a given period. The percentage exceeded corresponds to the subscript for each metric.
Level	A scale for describing the amplitude of acoustical quantities -usually 10 times the logarithm (base 10) of the ratio of an acoustical quantity of the same kind.
Metric	A measure of noise. Some metrics are complex and may account for characteristics such as noise duration, noise level, frequency content, time of occurrence, or single events.
Noise Level	The instantaneous sound pressure level defined as SPL = 10 log (P² /P² _ref) where P is acoustic pressure and P_ref is 20 micro-Pascals (20 µN/m or 2 x 10^-4 microbar). The frequency distribution of the pressure is usually A-weighted. A-weighted noise levels can either be calculated or measured using instrumentation with an A-weighting network.
NR	Abbreviation for Noise Reduction, the difference between the noise levels immediately outside and inside a structure. Noise reduction can be measured directly or calculated from known building properties.
Shielding	With respect to buildings, the tendency of the portions of a structure facing a noise source to attenuate the noise before it reaches portions of the structure not facing the noise source. The shielded building faces can be thought of as an "acoustical shadow."
STC	Abbreviation for Sound Transmission Class, a single-number rating describing the attenuation of wall- or panel-type structures.
TL	Abbreviation for Transmission loss, a rating of the attenuation of a particular type of wall construction.