Let’s say we double the intensity of a sound - what is the change in dB? If we double the intensity, our ratio is 2:1, where 2 is the louder sound and 1 is the initial sound, the point of reference. This value represents the dB intensity level. It’s important to account for this in our equation by multiplying the logarithm by 10 → To avoid the excess use of decimals, we simplify the bel into the decibel, which is one-tenth of a bel. It’s easier to represent the range of magnitudes, from barely audible to very loud, as 1 to 10 rather than 1 to 10,000,000,000,000! A change from 1 to 2 (1:2) is perceived as the same amount of increase as a change from 4:8 or 8:16. On a logarithmic scale, a change between two values is perceived on the basis of their ratio. For example, a change from 1 to 2 is perceived as the same amount of increase as a change from 2 to 3 or 3 to 4. On a linear scale, a change between two values is perceived by the difference between those values. Simply put, this is the logarithm of the ratio. ![]() Where N is number of bels, Ix is the intensity level of the sound in question and IR is our reference intensity, which, for our purposes, is the threshold of hearing, 1012Watts/m2 ![]() The human ear responds to a really wide range of intensity and pressure levels - a ratio of 1012 to 1! Instead of a linear value, it's much more convenient to express these relative magnitudes as a logarithmic value, which we call the bel, named after Alexander Graham Bell. Our threshold of hearing serves as a reference point upon which it can be based. The absolute power of a given sound doesn’t mean anything on it’s own. Our threshold of human hearing is 10-12 W - yes, one trillionth of a Watt.Īgain, when we talk about sound power level, we’re talking about the ratio of the power of a sound in comparison to our threshold of hearing. Compare this with an incandescent light bulb, which typically has 60 W of power. For example, the acoustic power of a lawn mower is about. In absolute terms, acoustic power is quite small. Sound intensity refers to the power per unit area, like Watts/m2 or Watts/cm2. So when we say “sound power” or “acoustic power” we’re referring to the total power produced by the sound source in all directions. Sound power is the rate at which that energy is transferred, measured with respect to the sound source. ![]() (power = work/time and pressure = force/unit area) We can measure sound as power (in Watts) or force (in Pascals) over an area. Let’s unpack this!Īs sound waves travel, the energy of air molecules propagates through the air. Sound levels are measured in decibels, but what does this actually mean?Ī decibel is a logarithmic unit of the ratio of two levels - the magnitude of a sound compared with a reference, which for our purposes would be the threshold of human hearing, the quietest possible sound we can perceive. In one of my courses this semester, I learned about a fundamental audio topic that, as silly as it sounds, I hadn't previously given enough thought - the decibel! ![]() This fall I began pursuing my doctorate of audiology at City University New York.
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