The range of sound intensities the human ear can detect is quite large. For example, at a frequency of 1 kHz, the intensity of the lowest sound you can hear is about 10^-12 W/m² and the intensity of the highest sound you can tolerate without pain is about 1 W/m².  Over this range, your perception of the sound loudness is not linear with the sound intensity. This allows your ear to be sensitive for very low sound intensities and at the same time be able to detect sounds which are 10¹² times as large in intensities. You need to increase the sound intensity roughly by 10 times for your ear to feel that its loudness is doubled.  Because of the huge range of the sound intensities you can hear and the way you perceive loudness, it is more convenient to use a logarithmic scale of sound intensities to express sound levels. The sound level b is defined as

where I₀ = 10^-12 W/m² is a standard reference intensity taken to be very close to the threshold of hearing. The unit of the sound level b is the decibel and its abbreviation is dB.  Decibel is formed from two words deci and bel.  Deci means part of 10 and bel refers to Alexander Graham Bell (1847-1922), the inventor of the telephone .  The sound level corresponds to I = I₀ is b= 10 log(I₀/I₀) = 0 dB and the sound level corresponds to the loudest sound you can tolerate is b = 10 log (1/I₀) = 120 dB. Thus, the sound level range for the sound you can hear is from 0 to 120 dB.  Since you need to increase a sound intensity roughly by ten times to feel that it is twice as loud, the loudness of a sound doubles with each increase in sound level of 10 dB.