decibels (Latin: "ten" plus "bel" [Alexander Graham Bell]; a list of decibel levels and the examples that show the various decibel scales).A decibel (pronounced: DES uh buhl), also known as a dB, is a unit for measuring the relative intensity of sounds, equal to one-tenth of a bel. A bel is used in physics to measure the difference in the intensity level of sounds to normal human ears, equal to ten decibels. It is estimated that 0 dB corresponds roughly to the quietest sound that can be heard by a healthy young adult. Normal conversation has a level of 60-70 dB, while sounds above about 100 dB tend to be uncomfortably loud and can damage our ears if heard for a long time. Sounds with a level above 120 dB can damage peoples' ears within quite a short time, perhaps only a few minutes. When the level of a sound is increased by 10dB, the subjective loudness roughly doubles, whereas the sound power actually increases by a factor of 10. The smallest detectable change in level is about 1dB. The system was named after Alexander Graham Bell [1847-1922], who is given credit for being the inventor of the telephone. "Numerous studies have shown prolonged exposure to 85 decibels or more can cause permanent hearing loss. Other physiological damage can occur at lower levels." "A single, explosive noise is capable of damaging hair cells, but hearing loss is usually the result of continual exposure to volumes over 80-85 decibels." (Vol. II, No. 8, 1986), pp. 1-4. 180 decibels, equivalent to a rocket launching pad [hearing loss inevitable]. 140 decibels, equivalent to a gunshot blast, jet plane take-off at close range [approximately 200 feet], air raid siren [any length of exposure time is dangerous and is at the threshold of pain]. 130 decibels, equivalent to sound vibrations felt, as with thunder or near a four-engine jet at thirty meters. 125 decibels, equivalent to a diesel engine room. 120 decibels, equivalent to an amplified rock concert in front of speakers, sand-blasting, thunderclap [immediate danger], a nearby airplane engine, some rock or hard-metal cacophony groups, pneumatic hammer at one meter, thunderclap over head [at around 120 dB, the sensation of hearing is replaced by that of pain]. 110 decibels, equivalent to deafening factory noises and some musical boxes turned up too loudly, discotheque, thunder, rock-n-roll band. 108 decibels, equivalent to the coqui frog croak of Puerto Rico [up to 108 dB]. 105 decibels, In a Malaysian surgical-glove factory, making surgical-latex gloves by dipping porcelain models of the human hand into liquid latex, which when dried, is blown off the hands by air jets. Before modifications to the air jets, the gloves were blown off every 30 seconds at a deafening 125 decibels. 100 decibels, equivalent to a chain saw, pneumatic drill, printing plant, jackhammer, speeding express train, some car horns at five meters, farm tractor, riveting machine, some noisy subways [about 20 feet]. 90 decibels, equivalent to a police whistle, heavy traffic, truck traffic, noisy home appliances subway-rail train, pneumatic drill [or hammer] at one meter, walk-man ear phone [average volume], rock drill at 100 feet, some motorcycles at 25 feet, shouted conversation. 80 decibels, equivalent to heavy city traffic [25-50 feet], alarm clock at two feet, factory noise, vacuum cleaner, heavy truck, loud-radio music, garbage disposal. 70 decibels, equivalent to typewriter, average factory noise, busy traffic [at one meter], office tabulator, noisy restaurant [constant exposure], quiet vacuum cleaner, TV. 60 decibels, equivalent to an air conditioner at twenty feet, conversation [at one meter], sewing machine, large transformer, ordinary or average street traffic. 50 decibels, equivalent to quiet radio, average home, light traffic at a distance of 100 feet, refrigerator, gentle breeze, average office, non-electric typewriter, ordinary spoken voice. 40 decibels, equivalent to quiet office, living room, bedroom away from traffic, residential area [no traffic]; many computer hard drives range an average of 40-50 dB, soft whisper [five feet]. 30 decibels, equivalent to quiet conversation, soft whisper, quiet suburb, speech in a broadcasting studio. 20 decibels, equivalent to whispering, ticking of a watch [by the ear], rural area [without loud farm machinery or other excessive noises]. 10 decibels, equivalent to the rustling of leaves. 0-1 decibels, equivalent to the faintest sounds that can be heard, the threshold of audibility. There are professional acoustic engineers who are in the business of "noisebusting" machinery used by individuals and production lines. Some noisebusting is pure decibel reduction to meet safety standards. OSHA, the Occupational Safety and Health Administration (a U.S. government agency), has limited workers' exposures to eight hours per day at sound levels of 90 decibels, four hours at 95 decibels and two hours at 100 decibels, with special limits for quick, sharp sounds, such as explosions. (The Reader's Digest, January, 1997), from Smithsonian, by Richard Wolkomir (February,1996). |