The volume of an audible sound or signal is relative. Although an increase in the sound pressure of 3 dB means that the sound energy has doubled, the human ear only senses that the volume has doubled when there has been an increase of 10 dB. Our sense of hearing can therefore be said to work on a logarithmic scale.
As well as the absolute volume of a signal, the perceived volume is also determined by the distance between the sounder and the person. When this distance is doubled, this equates to a 6 dB decrease in the sound pressure. The signal is then perceived to be about 25% quieter. The following range table can be used as a basis for estimating the sound level.
These values only serve as a guideline, however, as environmental factors such as wind speed, wind direction, humidity and weather conditions do also have an effect on audible signals.