sound pressure level

n. (SPL) The absolute intensity of a sound in decibels relative to the standard of 10−16 watts per square centimeter, which is just below the human capacity to hear at 1,000 hertz, which is about two octaves above middle C on a piano. A sound of 100 dB SPL is 100 watts per square centimeter above the standard. Because 3 dB corresponds to a factor of 2 in SPL, a sound at 6 dB SPL is twice as loud as a sound at 3 dB SPL and half as loud as a sound at 9 dB SPL.