Hearing by the Numbers: The Decibel Scale

When we talk about measuring sound, the unit we use is called a decibel. The decibel scale is based on the sounds our ears can hear in increasing intensity: this is quite a wide range to cover, as the human ear is highly sensitive.


How is sound measured?


The lowest level on the decibel scale is 0, which is almost total silence. This is the measurement of the softest sound that our ears can hear. With each increase of 10 decibels, a sound becomes 10 times more intense and twice as loud to our ears. By the time the decibel level reaches about 120 decibels, such as the sound of an ambulance siren or a jet engine, the intensity is 1 trillion times greater than the weakest audible sound.

Since decibel levels can be harder for us to estimate than distance or volume, many hearing organizations have developed helpful points of reference on the decibel scale. The sound of normal breathing is 10 decibels, a soft whisper is 30 decibels, a normal conversation is 60 decibels, and shouting in the ear is 110 decibels. Among common environmental sounds, a refrigerator is 50 decibels, a ringing telephone is 80 decibels, a noisy restaurant is 85 decibels, and a subway is 90 to 115 decibels.

What does this mean for my hearing health?


So, how does the decibel scale impact you and your hearing health? Experts have determined that any sound over 85 decibels can cause hearing loss, although the extent of any damage will naturally depend on both the power of the sound and how long and frequently you are exposed to it. (The National Institute for Occupational Safety and Health suggests a maximum of 8 hours of exposure to sounds of 85 decibels. For sounds of 110 decibels, the maximum exposure time is 1 minute and 29 seconds.)

As a general guideline, your environment is considered too loud when you cannot hear or be heard by someone standing less than 3 feet away from you, when the noise hurts your ears or makes your ears buzz or ring, or when regular sounds and speech seem muffled or dull even after you have left the loud environment.

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