Sound pressure level
The sound pressure level is defined as the change in pressure caused by the molecules of air oscillating. The range of sound pressures that our ears can identify lies between 2x10exp-5 N/m² and 20 N/m² (at 1000 Hz). This is equivalent to a factor of 1,000,000. In order to make it easier to perform mathematical calculations in this range, the decibel (dB) was introduced as the logarithmic equivalent, or volume level. In this way, a sound pressure of 2x10exp-5 N/m² is equivalent to a volume level of 0 dB, a sound pressure of 20 N/m² means a volume level of 120 dB. A change in sound pressure of 10 dB is perceived as a doubling of the volume. A change of 3 dB is clearly audible. Smaller changes in volume level are generally only perceived in a direct comparison.