Decibel a scale4/13/2024 ![]() ![]() While sound intensity (in W/m 2) is the SI unit, the sound intensity level in decibels (dB) is more relevant for how humans perceive sounds. The decibel equation can also be written in terms of a change. You may have noticed that when people talk about the loudness of a sound, they describe it in units of decibels rather than watts per meter squared. For instance, any increase by 5 dB represents an increase in intensity by a factor of 3.16. Similarly, a 60 dB sound has ten times the intensity of a 50 dB sound, and 1/10th the intensity of a 70 dB sound.Īn increase of x dB means that the sound has increased in intensity by some factor. Any more intense than this and sounds start getting uncomfortable.Īn earthquake measuring 6.0 on the Richter scale is 10 times more powerful as one measuring 5.0, and 1/10th as powerful as one measuring 7.0. 120 dB, 12 orders of magnitude higher than our reference level, has an intensity of 1 W/m 2. Every 10 dB represents a change of one order of magnitude in intensity. This is around the lowest intensity sound we can hear, and it works out to 0 dB. A decibel level of 120 is nearly 1 million times greater in terms of sound. ![]() With every 6.02 dB, the sound pressure actually doubles or with a -6.02 dB, the sound pressure actually halves. This means that the intensity (amplitude) of a sound increases more quickly than the numbers along the decibel scale. Where I is the intensity in W/m 2 and I o is a reference intensity known as the threshold of hearing. The decibel scale is a logarithmic scale. This is why we use the decibel scale - much like the Richter scale for measuring earthquakes, the decibel scale is logarithmic. The ear can do this because it responds to sound intensity logarithmically. ![]() It can handle sound with frequencies covering three orders of magnitude, and intensities covering 12 orders of magnitude! The human ear is actually an amazing instrument. ![]()
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