Photo of saxophones to illustrates sound pressure

The decibel is a unit of measure of sound. Its scale is not linear, it is logarithmic. Therefore, its manipulation is not always very intuitive.

Here are some important rules:

  • We double energy at the sound source when sound is increased by only 3 dB. In this way, two saxophones playing at 60 dB produce a sound of 63 dB and not 120 dB. Conversely, if sound increases by 3 dB (for example in a nightclub) we multiply the sound energy by 2, so the safe listening time is diminished by 2.
  • We multiply sound energy at the source by 10 when we increase the sound by 10 dB.
  • When we combine 2 sources of sound of different intensities, the resulting intensity will be about equal to that of the strongest source. In our example an alto saxophone plays at 60 dB and a tenor sax plays at 70 dB at the same time, producing a combined sound of 70 dB.
  • The sound decreases by 6 dB when doubling the distance from the source.

In addition to these mathematical rules, we must add the particular functioning of our ear and its way of perceiving sound. This is what is called psychoacoustics. In other words we can say that each time that the sound level increases by 10 dB, we hear 2 times louder. In these terms sound of 100 db is heard 4 times louder than sound of 80 dB.

Reference points on the decibel scale

  • 0   dB: Normal hearing
  • 65 dB: Normal level for conversation
  • 80-85 dB: Below risk level for injury
  • 110 dB: This is the limit after which there is a potential  risk
  • 120 dB: Threshold For Auditory pain.

A rock group plays between 85 and 105 dB. These sound levels present a risk for the inner ear, and the risk increases according to increased rates of exposure. Moreover, we are not equal when faced with an auditory trauma, certain people are more sensitive than others.  As a result, not all  band members  who are exposed to the same loud noise will suffer the same consequences as another band member.