The sound pressure 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. 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.