Physics
Decibel (dB)
Quick fact
A 3 dB increase corresponds to a doubling of sound intensity, but the human ear perceives it as only a slight increase in loudness.
Why this is interesting
Ever wondered why a whisper is 30 dB and a rock concert is 120 dB, yet a 10 dB increase doesn’t mean it sounds twice as loud—but actually 10 times more intense?
Read the full explanation
Understanding Decibel (dB)
The decibel is not a linear unit like meters or kilograms. Instead, it compares two quantities on a logarithmic scale. For sound, the reference is typically the threshold of hearing (0 dB = 20 micropascals). Every 10 dB increase means the sound intensity has multiplied by 10. Because our ears respond to a huge range of pressures (from the faintest whisper to a jet engine), the logarithmic scale collapses that range into a convenient 0–140 dB scale. To compute dB, you take the logarithm of the ratio of two powers: dB = 10 × log10(P/P₀). For pressure or amplitude, the formula becomes 20 × log10(p/p₀) because power is proportional to the square of pressure.
A deeper explanation
The decibel originated in telecommunications to measure signal loss in cables, but its use in acoustics is tied to the Weber–Fechner law: the just noticeable difference in a stimulus is proportional to the size of the stimulus. That means perceived changes are logarithmic, making dB a natural fit. More formally, the dB is a dimensionless unit expressing a ratio. It matters because it allows engineers and scientists to think about large dynamic ranges (e.g., 0 dB SPL to 120 dB SPL) without dealing with huge numbers. In electronics, dB is used for gain, attenuation, and signal-to-noise ratio, unifying comparisons across different systems. Understanding the decibel is thus essential for anyone working with sound, communications, or any field where relative intensity matters.