Measurement in decibels of the pressure or force exerted by a sound wave on the environment with increasing pressure generating increased loudness or higher volume (creating more pressure in the ear increases perceived loudness). Sound pressure level is essentially how loud a sound is. Very loud sounds, such as jet engines, have high sound pressure levels. Conversely, soft sounds have low sound pressure levels. he loudness of a sound (its SPL or sound pressure level) can be read by a SPL meter. The pressure level is measured in decibels with zero decibels being the threshold of human hearing (a just barely audible sound). The maximum level of human hearing is around 120 decibels sound pressure level, which is the level where people begin to experience pain due to the high sound pressure levels. he decibel scale is logarithmic meaning that a 10 decibel increase in sound pressure level is a doubling of the perceived sound pressure level (this doubling requires using 10 times the acoustic power however). Thus, the scale remains fairly low until around 60 dB or so where it begins to slope up much more steeply. For instance, doubling 1 only gets 2, doubling 2 gets 4, doubling 4 gets 8, doubling 8 get 16, doubling 16 gets 32 – at first the increases are small with a shallow slope, but they quickly build after a certain threshold gaining very rapidly at some point. he smallest change in sound pressure level the ear can detect is one decibel. Some examples of sound pressure levels are: whisper – 20 dB, normal speech – 70 dB, passing subway train – 100 dB, large jet plane – 120 dB. ounds become quieter as we move farther from the source. Each doubling in distance from a sound source results in a loss of 6 dB of sound pressure.