Sound Pressure Levels

Sound pressure or sound pressure level is the result of the variations of pressure in the air, achieved by the sound waves.

The sound is an auditory sensation caused by vibration and an acoustic wave frequency between 20 Hz and 20,000 Hz, propagating in a solid, liquid or gaseous medium. Contrary to electromagnetic waves (light waves, radio waves, etc.), propagating the sound requires a medium. When the excitation frequencies of the acoustic phenomenon are below 20 Hz, we can speak of an infrasound. When they are greater than 20,000 Hz., it is an ultrasound.

The magnitude measured with a microphone sound pressure is normally effective. The pressure can reveal all the other quantities, but as the field values of the sound pressure are very large (there are pressure variations ranging from 0.00002 to 200 Pascals) a new magnitude practice in the sound pressure level in decibels or dB was introduced, which is compared to a pressure corresponding to the hearing threshold and equal to the reference pressure. This changes the pressure scale’s linear logarithmic pressure and simplifies the way you work with pressure, noise or sound.

SPL = Sound pressure level

SPL = Sound Pressure Level

Therefore we can conclude that:

A margin pressure of 20 mPa (threshold of hearing) to 200 Pa (pain threshold) is audible.
There is a rage of very large numerical values to work with (from 0.00002 to 200 Pa).
The audible frequency ranges between 20 Hz and 20,000 Hz.

The appearance of the logarithmic scale, which applies a logarithmic weighting of the decibels, simplifies the following:

Working with Pascal or other unit of pressure is uncomfortable for a great variety of values (between 2.10-5 and 200 Pa).
With this form of expression, the noise margin is set between 0 and 140 dB.

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