Sound Pressure Level (SPL)

음압이란 음파가 매질속을 지날 때 매질의 각 질점에서 발생하는 압력의 변화량을 말한다. 음압은 공기중에서는 마이크로폰, 수중에서는 하이드로폰으로 측정할 수 있다. 단위는 파스칼(Pa) 등으로 표시한다.

음압 레벨은 음압과 기준 음압과의 비율을 로그 규모로 표현한 것을 말한다. 단위는 데시벨(dB)을 쓴다.

음압 레벨(sound pressure level) L_p은 음압과 기준 음압 p_ref과의 비율을 로그 규모로 표현한 것을 말하며, 이 때 음압은 실효값(root mean square)을 쓴다.

기준 음압은 공기 중의 음파일 경우 p_ref = 20 µPa를 쓰는데, 이는 1kHz에서의 최소 가청치를 기준으로 한 것이다.

음압 레벨의 단위는 데시벨(dB)을 사용하며, 음압 레벨임을 밝혀주기 위해 dB (SPL) · dBSPL · dB_SPL 등의 표기를, 특별히 기준 음압을 밝혀줄 때에는 dB re 20 µPa · dB (20 µPa) 등의 표기를 쓴다.

(출처: http://ko.wikipedia.org/wiki/%EC%9D%8C%EC%95%95)

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Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level.

where pref is the reference sound pressure and prms is the rms sound pressure being measured.

Sometimes variants are used such as dB (SPL), dBSPL, or dBSPL. These variants are not recognized as units in the SI.

The unit dB (SPL) is often abbreviated to just "dB", which can give the erroneous impression that a dB is an absolute unit by itself. The commonly used reference sound pressure in air is pref = 20 µPa (rms), which is usually considered the threshold of human hearing (roughly the sound of a mosquito flying 3 m away). Most sound level measurements will be made relative to this level, meaning 1 pascal will equal 94 dB SPL. In other media, such as underwater, a reference level of 1 µPa is more often used.

Ears detect changes in sound pressure. Human hearing does not have a flat spectral sensitivity (frequency response) relative to frequency versus amplitude. Humans do not perceive low- and high-frequency sounds as well as sounds near 2,000 Hz, as shown in the equal-loudness contour. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring sound pressure: A, B and C. A-weighting applies to sound pressures up to 55 dB SPL, B-weighting applies to sound pressures between 55 and 85 dB SPL, and C-weighting is for measuring sound pressure above 85 dB SPL.

(출처: http://en.wikipedia.org/wiki/Sound_pressure_level#Sound_pressure_level)