Measuring sound pressure levels is complex and requires complicated calculations. The
decibel scale was introduced to make measurements easier for us to grasp. It looks at the unique capability of
human hearing to strongly differentiate low sound levels while even large differences in sound pressure are not as precisely perceived in the high decibel range.
Using various filters, particularly low or high frequencies are reduced or regulated depending on our perception. The value on the scale thus corresponds more with our perceptions and is made measurable. dB values are most often given in dB (A) – the A standing for the use of the A filter, the so-called sound level evaluation curve A.
Decibel values are only linear at first glance – 120 dB would seem to be twice as loud as 60 dB but that’s not the case. The decibel scale is structured logarithmically. For measured values this means that a circular saw is not just twice as loud as talking but that its relative sound pressure is actually approx. 1,000 times as high.
Apart from this so-called dB(A) scale to measure noise, there is the dB(HL) scale used by
audiologists and hearing acousticians to determine hearing loss.
Leaves rustling in the wind, a gnat or modern computers only measure a measly 10 dB, for instance. Whispering reaches 30 dB and regular talk roughly 60 dB. Screaming babies and motorcycles score 80 dB. Those who love to frequent night clubs are subjected to the same (110 dB) noise level that jackhammers and circular saws produce.
The noise created by jet planes – roughly 130 dB – is where our pain threshold starts. Slaps in the face and firecrackers going off right next to the ear are extremely loud and harmful. They reach dB values of up to 180. The extent to which we feel sound, meaning how disruptive it is to us, is also influenced by the distance between the source of the sound and our hearing system.