Text: [Acoustics] The ratio, expressed in decibels, of mean square sound pressure to a reference mean square pressure which by convention has been selected to be equal to the assumed threshold of hearing. Lp = 10 log10(P/Pref)2 = 20 log(P/Pref) where: Lp = sound pressure level P = root mean square sound pressure Reference pressure: Pref = 2 x 10-5 N/m2 = 0.0002 dynes/cm2 = 0.0002 microbars = 20 micropascals (rms)

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