What is a Decibel?
A decibel (dB) is a logarithmic unit used to measure sound intensity or loudness. Because human hearing can perceive an enormous range of sound pressures, from the faintest whisper to a jet engine, a linear scale wouldn't be practical. The decibel scale compresses this vast range into a more manageable set of numbers, reflecting how humans perceive loudness, where a small change in dB represents a large change in sound power.
The Logarithmic Nature of Decibels
The decibel scale is logarithmic, meaning that a 10 dB increase represents a tenfold increase in sound power or intensity, and roughly a doubling in perceived loudness. For instance, 60 dB is ten times more intense than 50 dB, and 70 dB is one hundred times more intense than 50 dB. This mathematical approach helps quantify very large and very small values effectively, aligning with the non-linear way our ears respond to sound.
Decibels in Everyday Life
Decibels are commonly used to describe the noise levels of various environments and activities. A quiet whisper might be around 30 dB, normal conversation 60 dB, a busy street 80 dB, and a rock concert often exceeds 100 dB. Prolonged exposure to sounds above 85 dB can cause permanent hearing damage, highlighting the importance of understanding decibel levels for health and safety.
How Decibels Are Measured
Decibels are typically calculated by comparing a measured sound pressure level to a reference sound pressure level, usually the threshold of human hearing (0 dB). This is expressed by a formula involving logarithms: L(dB) = 10 * log10(P/P0) for power, or L(dB) = 20 * log10(V/V0) for amplitude (like sound pressure), where P0 or V0 is the reference level. Specialized instruments called sound level meters are used to take these measurements.