Editing Noise pollution (section)

====Sound level meters====
Sound can be measured in the air using a [[sound level meter]], a device consisting of a microphone, an [[amplifier]], and a time meter.<ref>{{cite book |last1=Webster |first1=Roger C. |title=Plant Engineer's Handbook |year=2001 |isbn=978-0-7506-7328-0 |pages=707–719 |chapter=Noise and Vibration |doi=10.1016/b978-075067328-0/50044-6}}</ref> Sound level meters can measure noise at different frequencies (usually A- and C-weighted levels).<ref name=":02" /> There are two settings for response time constants, fast (time constant = 0.125 seconds, similar to human hearing) or slow (1 second, used for calculating averages over widely varying sound levels).<ref name=":02" /> Sound level meters meet the required standards set by the International Electrotechnical Commission (IEC)<ref>{{Cite web |title=IEC 61672-1:2013 {{!}} IEC Webstore |url=https://webstore.iec.ch/publication/5708 |url-status=live |archive-url=https://web.archive.org/web/20210126101227/https://webstore.iec.ch/publication/5708 |archive-date=2021-01-26 |access-date=2020-11-29 |website=webstore.iec.ch}}</ref> and in the United States, the American National Standards Institute as type 0, 1, or 2 instruments.<ref name=":13">{{Cite web |date=1983 |title=ANSI S1.4-1983, Specification for Sound Level Meters |url=https://law.resource.org/pub/us/cfr/ibr/002/ansi.s1.4.1983.pdf |url-status=live |archive-url=https://web.archive.org/web/20210211011219/https://law.resource.org/pub/us/cfr/ibr/002/ansi.s1.4.1983.pdf |archive-date=2021-02-11 |access-date=2020-11-28 |website=American National Standards Institute}}</ref>

Type 0 devices are not required to meet the same criteria expected of types 1 and 2 since scientists use these as laboratory reference standards.<ref name=":13" /> Type 1 (precision) instruments are to study the precision of capturing sound measurements, while type 2 instruments are for general field use.<ref name=":13" /> Type 1 devices acceptable by the standards have a margin of error of ±1.5&nbsp;dB, while type 2 instruments meet a margin of error of ±2.3&nbsp;dB.<ref name=":13" />