Online Tone Generator
What is a decibel?
The internet is full of overly complicated explanations of this widely used but rarely understood unit of measurement.
Firstly, it is important to understand exponents and logarithms. Here's a simple example: Here, the little 2 is called the exponent. It means multiply 10 by itself twice. Similarly, for: 3 is the exponent, and means multiply 10 by itself 3 times.
A logarithm is the exact opposite of an exponent. Take another simple example. This is pronounced "the logarithm to base ten of one thousand equals three":10 is called the base. The logarithm of 1000 is simply the number of times the base (in this case 10) must be multiplied by itself to get to 1000, i.e. 3 times. And you should notice that this is just the same as the exponent from the equation above. Each equation uses the same three numbers, just arranged in a slightly different way.
Now, the strange thing is that exponents and bases don't have to be whole numbers. In fact, they can be any numbers at all. Here is a completely random example: One important rule to learn is that the logarithm of 1 is always zero, regardless of its base.
The decibel (dB) is one tenth of a bel and is named in honour of Alexander Graham Bell. The intensity in dB of a sound of intensity I is given by It is a relative unit which means it only makes sense when you have a reference level to compare to. For our reference we use the threshold of human hearing. The quietest thing any human can hear, I0, is one trillionth of a watt per square meter. So, if a sound is twice as intense as I0, its intensity will be
|Scenario||Number of times more intense than I0||Intensity in dB|
|Limit of human hearing||1||0|
|Sound of Breathing||10||10|
|Jet Plane on Take-off||100,000,000,000,000||140|
|Space Rocket Launch||10,000,000,000,000,000,000||190|