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The decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. Until the mid-1920s, the unit for loss was miles of standard cable (MSC). 1 MSC corresponded to the loss of power over one mile (approximately 1.6 km) of standard telephone cable at a frequency of 5000 radians per second (795.8 Hz), and matched closely the smallest attenuation detectable to a ...
Noise may be measured using a sound level meter at the source of the noise. [23] [24] [25] Alternatively, an organization or company may measure a person's exposure to environmental noise in a workplace via a noise dosimeter. [26] The measurements taken using either of these methods will be evaluated according to the standards below.
The SI unit of intensity, which includes sound intensity, is the watt per square meter (W/m 2). One application is the noise measurement of sound intensity in the air at a listener's location as a sound energy quantity. [3] Sound intensity is not the same physical quantity as sound pressure. Human hearing is sensitive to sound pressure which is ...
Examples of electrical noise-level measurement units are dBu, dBm0, dBrn, dBrnC, and dBrn(f 1 − f 2), dBrn(144-line). Noise may also be characterized by its probability distribution and noise spectral density N 0 (f) in watts per hertz. A noise signal is typically considered as a linear addition to a useful information signal.
A noise dosimeter (American) or noise dosemeter (British) is a specialized sound level meter intended specifically to measure the noise exposure of a person integrated over a period of time; usually to comply with Health and Safety regulations such as the Occupational Safety and Health (OSHA) 29 CFR 1910.95 Occupational Noise Exposure Standard ...
The centimeter-gram-second system of units, the reference sound pressure for measuring ambient noise level is 0.0002 dyn/cm 2, or 0.00002 N/m 2. [6] 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 ...