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DECIBELS 16th January 2012
The decibel, or dB, is a means of expressing either the gain of an active device (amplifier) or the loss in a passive device (attenuator). The decibel was developed by the telephone company to conveniently express the gain or loss in telephone transmission systems.
Since the range of intensities that the human ear can detect is so large, the scale that is frequently used by physicists to measure intensity is a scale based on multiples of 10. This type of scale is sometimes referred to as a logarithmic scale. The scale for measuring intensity is the decibel scale.
The intensity of a sound reaching a persons ear depends not only on the intensity of the sound produced, but also on the persons distance from the source of the sound. If you were standing one foot away from a loud machine, for instance, you would experience higher decibel level than if you were ten feet away, even though the intensity of the sound produced remains unchanged. This is so because the intensity of sound decreases as sound waves spread out over time and distance. The intensity of sound is measured in a unit called the decibel (dB), which describes the relative intensity of a sound based on an algorithmic decibel scale containing values ranging from 0 to 194.
The important thing to know about the decibel is that it represents a ratio, not an amount. In other words, there is not an amount of energy called a decibel that can be added or subtracted to achieve a different volume. Instead, a decibel compares the loudness of two different sounds. When we want to determine a noises decibel level, we must compare it to a certain predetermined baseline.
Humans are equipped with very sensitive ears capable of detecting sound waves of extremely low intensity. This faintest sound that a human ear can detect is known as the threshold of hearing. The most intense sound that the ear can safely detect without suffering any physical damage is more than one billion times more intense than the threshold of hearing.
On the decibel scale, the smallest audible sound (threshold of hearing) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB and so on. The average human range of hearing is about zero decibels to 120 decibels. Past this point, sound becomes painfully loud and may cause permanent damage to the ears.