Decibels & Pascals
and what does 0dB really mean?
What exactly is a Pascal?
Sound pressure is usually measured in pascals, which is an SI (metric) unit. This calculates the amount of force per unit area. Thing is, the human ear is so sensitive that it can pick up as little as 20 micropascals (0.000020 Pa)! This makes expressing i.e. the sound of leaves rustling (0.0000632 Pa) vs the sound of an extremely loud band (200 Pa) inconvenient and difficult to interpret. So they devised a logarithmic scale, the Decibel, to make working with these numbers more manageable.
Okay fine, so what is a Decibel?
The intensity (volume) of sound is measured in decibels (dB).
The decibel scale is a little odd because it was devised to express the hearing range of humans. Again, since the human ear is incredibly sensitive, it can pick up as little as 20 micropascals (0.000020 Pa). This is used as the reference level for decibels (dB), so 0.000020 Pa = 0 dB.
Here’s an example of how some typical sound pressures are expressed in Pascals and Decibels:
Common sounds measured in Pascals and Decibels
As you can see, we now have a range of numbers that seems more convenient – from 10 to 150 – instead of a range from a very, very, small number to a number in the hundreds.
The drawback, however, is that the scale with decibels is not linear, but rather logarithmic. So 90dB, the volume of the average lawnmower, is 1,000,000,000 times more powerful than near total silence!
So don’t scoff when someone tells you that “it’s only 10dB louder”. Every increase in 3dB doubles the sound intensity, and therefore halves the amount of time that you can be exposed to it before you use up your noise dose!
You'll also notice that the sound pressure drastically increases when a jet engine is 1m away, as opposed to 100m. This is because every doubling of the distance from the source halves the sound (inverse square law). So if you're standing right in front of speakers at a gig with no hearing protection available, sometimes just walking a few steps back is all you really need to help protect your ears from harmful levels.
Now that you understand what decibels mean and why 85dB + 85dB = 88dB, learn how you can easily measure sound.. for free! Or skip ahead and check out how hearing relates to stress, fatigue, depression and even obesity.
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