ambient noise level

{{Short description|Background sound pressure level}}

Image:Integrating Sound Level Meter dB(A) Brüel Kjær 2225.jpg

In atmospheric sounding and noise pollution, ambient noise level (sometimes called background noise 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.{{cite web|url=https://gracey.co.uk/basics/background-noise-b1.htm|title=Sound and Vibration Instrument Hire and Calibration Background Noise Measurement|access-date=22 October 2021|publisher=Gracey & Associates}}

Ambient sound levels are often measured in order to map sound conditions over a spatial regime to understand their variation with locale.{{cite journal|issn=2006-0459|url=http://repository.futminna.edu.ng:8080/jspui/handle/123456789/12697|publisher=SCHOOL OF ENVIRONMENTAL TECHNOLOGY, FUT MINNA|title=SPATIAL ANALYSIS AND GEOGRAPHICAL INFORMATION SYSTEM (GIS) MAPPING OF NOISE POLLUTION IN BOSSO LOCAL GOVERNMENT COUNCIL, NIGER STATE, NIGERIA|first1=S.A|last1=Jonah|first2=A.N|last2=Baba-Kutigi|first3=U.E|last3=Uno|first4=M.L|last4=Dangana|first5=M.T|last5=Kolo|first6=N.P|last6=Ofor|first7=C.I|last7=Unuevho|first8=F.M|last8=Abba|first9=D.U|last9=Alhassan|first10=A.N|last10=Amadi|first11=M.O|last11=Umar|first12=M.I|last12=Kimpa|journal=Environmental Technology & Science Journal |date=2011}} In this case the product of the investigation is a sound level contour map.{{cite journal|url=https://web.s.ebscohost.com/abstract?direct=true&profile=ehost&scope=site&authtype=crawler&jrnl=15829596&AN=34525080&h=mw0NZuMmyhIpTu6JFbUaIeHMbta4i%2fUFwUQ%2fhcnJBxT51m8eWGsHEFySYISTZ2DHMZNZSi%2bCdYcgRwQXq2C6rA%3d%3d&crl=c&resultNs=AdminWebAuth&resultLocal=ErrCrlNotAuth&crlhashurl=login.aspx%3fdirect%3dtrue%26profile%3dehost%26scope%3dsite%26authtype%3dcrawler%26jrnl%3d15829596%26AN%3d34525080|journal=Environmental Engineering & Management Journal|first1=Cahit Tagi|last1=Celik|first2=Lale|last2=Guremen|title=Analytical Noise Contour Construction Using Inverse Square Law of Sound Propagation |date=2008|issue=4|volume=7|pages=423–426|doi=10.30638/eemj.2008.061 |bibcode=2008EEMJ....7..423C }} 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 is studied by measuring ambient sound without presence of any overflights, and then studying the noise addition by measurement or computer simulation of overflight events. Or roadway noise is measured as ambient sound, prior to introducing a hypothetical noise barrier intended to reduce that ambient noise level.

Ambient noise level is measured with a sound level meter. It is usually measured in dB relative to a reference pressure of 0.00002 Pa, i.e., 20 μPa (micropascals) in SI units. This is because 20 μPa is the faintest sound the human ear can detect.{{cite web|url=https://heartaudio.co.nz/what-decibels-pascals-means|publisher=HeartAudio|title=Decibels & Pascals|access-date=22 October 2021}} A pascal is a newton per square meter. The centimeter-gram-second system of units, the reference sound pressure for measuring ambient noise level is 0.0002 dyn/cm², or 0.00002 N/m².{{cite web|url=https://www.justintools.com/unit-conversion/pressure.php?k1=micropascals&k2=newton-per-square-meter|publisher=Justin Tools|title=PRESSURE Units Conversion micropascals to newton-per-square-meter|access-date=22 October 2021}} Most frequently ambient noise levels are measured using a frequency weighting filter, the most common being the A-weighting scale, such that resulting measurements are denoted dB(A), or decibels on the A-weighting scale.{{cite web|url=https://www.nexflow.com/blog/what-does-dba-mean/|title=What does dBA mean when someone talks about noise levels?|date=November 6, 2018|publisher=Nex Flow|access-date=22 October 2021}}