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HOW LOUD IS TOO LOUD?
Experts agree that continued exposure to noise above 85 dBA over time, will cause hearing loss. To know if a sound is loud enough to damage your ears, it is important to know both the loudness level (measured in decibels, dBA) and the length of exposure to the sound. In general, the louder the noise, the less time required before hearing loss will occur. According to the National Institute for Occupational Safety and Health (1998), the maximum exposure time at 85 dBA is 8 hours. At 110 dBA, the maximum exposure time is one minute and 29 seconds. If you must be exposed to noise, it is recommended that you limit the exposure time and/or wear hearing protection. A person talking measures about 50 dB. It is a reasonably comfortable level of sound. You might think that ten people talking would be ten times louder. However, if you think of your experience, this is not the case. Ten people talking (in a classroom, for example) is louder than one person, but it isn’t ten times louder. This is because of the way that your ear and brain pick up sounds and interpret them.
As a rule of thumb, every ten decibel increase seems about twice as loud. However, this will vary from person to person and also depends on the pitch of a sound. So a 20 dB increase would be 100 times as powerful (10x10) but sound about 4 times as loud (2x2)
In noise reduction terms a 3dB reduction is actually a 50% reduction in the sound power level of the noise. A reduction of 10dB is an SPL reduction of 90%.