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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 ...
A-weighting is only really valid for relatively quiet sounds and for pure tones as it is based on the 40-phon Fletcher–Munson equal-loudness contour. [3] The B and C curves were intended for louder sounds (though they are less used) while the D curve is used in assessing loud aircraft noise ( IEC 537 ).
A graph of the A-, B-, C- and D-weightings across the frequency range 10 Hz – 20 kHz Video illustrating A-weighting by analyzing a sine sweep (contains audio). A-weighting is a form of frequency weighting and the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. [1]
The decibel watt (dBW or dB W) is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt.It is used because of its capability to express both very large and very small values of power in a short range of number; e.g., 1 milliwatt = −30 dBW, 1 watt = 0 dBW, 10 watts = 10 dBW, 100 watts = 20 dBW, and 1,000,000 W = 60 dBW.
Dynamic range (abbreviated DR, DNR, [1] or DYR [2]) is the ratio between the largest and smallest measurable values of a specific quantity. It is often used in the context of signals, like sound and light.
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In general, the interior of an anechoic chamber can be very quiet, with typical noise levels in the 10–20 dBA range. In 2005, the best anechoic chamber measured at −9.4 dBA. [2] In 2015, an anechoic chamber on the campus of Microsoft broke the world record with a measurement of −20.6 dBA. [3]
Originally, the A-weighting was only meant for quiet sounds in the region of 40 dB sound pressure level (SPL), but is now mandated for all levels. C-weighting is however still used in the measurement of the peak value of a noise in some legislation, but B-weighting – a halfway house between 'A' and 'C' has almost no practical use.
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