Ambient noise level - AbsoluteAstronomy.com

Atmospheric sounding

An atmospheric sounding is a measurement of vertical distribution of physical properties of the atmospheric column such as pressure, temperature, wind speed and wind direction , liquid water content, ozone concentration, pollution, and other properties...

and noise pollution

Noise pollution

Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...

, ambient noise level (sometimes called background noise
Background noise
In acoustics and specifically in acoustical engineering, background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise regulations...

level, reference sound level, or room noise level) is the background sound pressure level at a given location, normally specified as a reference level to study a new intrusive sound source.

Ambient sound levels are often measured in order to map sound conditions over a spatial regime to understand their variation with locale. In this case the product of the investigation is a sound level contour map

Contour line

A contour line of a function of two variables is a curve along which the function has a constant value. In cartography, a contour line joins points of equal elevation above a given level, such as mean sea level...

. Alternatively ambient noise levels may be measured to provide a reference point for analyzing an intrusive sound to a given environment. For example, sometimes aircraft noise

Aircraft noise

Aircraft noise is noise pollution produced by any aircraft or its components, during various phases of a flight: on the ground while parked such as auxiliary power units, while taxiing, on run-up from propeller and jet exhaust, during take off, underneath and lateral to departure and arrival paths,...

is studied by measuring ambient sound without presence of any overflights, and then studying the noise addition by measurement or computer simulation

Computer simulation

A computer simulation, a computer model, or a computational model is a computer program, or network of computers, that attempts to simulate an abstract model of a particular system...

of overflight events. Or roadway noise

Roadway noise

Roadway noise is the collective sound energy emanating from motor vehicles. In the USA it contributes more to environmental noise exposure than any other noise source, and is constituted chiefly of engine, tire, aerodynamic and braking elements...

is measured as ambient sound, prior to introducing a hypothetical noise barrier

Noise barrier

A noise barrier is an exterior structure designed to protect sensitive land uses from noise pollution...

intended to reduce that ambient noise level.

Ambient noise level is measured with a sound level meter

Sound level meter

Sound level meters measure sound pressure level and are commonly used in noise pollution studies for the quantification of almost any noise, but especially for industrial, environmental and aircraft noise. However, the reading given by a sound level meter does not correlate well to...

. It is usually measured in dB

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

above a reference pressure level of 0.00002 Pa, i.e., 20 μPa (micropascals) in SI units

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

. A pascal is a newton per square meter. The centimeter-gram-second system

System

System is a set of interacting or interdependent components forming an integrated whole....

of units, the reference level for measuring ambient noise level is 0.0002 dyn/cm². Most frequently ambient noise levels are measured using a frequency weighting filter, the most common being the A-weighting

A-weighting

A Weighting curve is a graph of a set of factors, that are used to 'weight' measured values of a variable according to their importance in relation to some outcome. The most commonly known example is frequency weighting in sound level measurement where a specific set of weighting curves known as A,...

scale, such that resulting measurements are denoted dB(A), or decibels on the A-weighting

A-weighting

scale.

See also