Humans have a very wide range of hearing when measuring intensity in units of Watts per meter. For this reason, a logarithmic unit of measurement called sound intensity level is often used for measuring loudness. The unit for sound intensity level is the bel or decibel (dB).
\(I_0\) is a very small intensity, at the lower limit of human hearing. When \(I = I_0\text{,}\) it does not mean there are no sound waves present, just that humans cannot hear them.
When the sound intensity level increases by 10 dB, the intensity increases by a factor of ten. You start to feel pain from high intensity sound at about 130 dB
