The unit for measuring the loudness of sound is the decibel. This unit is one-tenth of a Bel. The Bel was named in honor of Alexander Graham Bell, the inventor of the telephone and phonograph.
Sounds at 0 decibels are at the threshold for human hearing. Those at 140 decibels cause pain to the hearer. Sounds above 85 decibels cause hearing damage. At 100 decibels, sound results in permanent hearing damage in only 15 minutes. Sounds above 120 decibels often result in immediate damage to the hearing. Talking in normal tones occurs at 60 decibels, a level safe for one's hearing.