20dB

20dB, or twenty decibels, is a unit expressing sound intensity or power ratio in a logarithmic scale. The decibel (dB) originates from the Greek word "decimus," meaning tenth, and was introduced in the early 20th century as a convenient logarithmic measure for engineering applications. One ear‑noise unit (EN) is defined as that intensity which a person at a 1‑meter distance hears as loud as an international standard neon lamp, roughly equaling 17 dB of background noise over an audible frequency range.

In acoustics, sound pressure levels are calculated with the formula Lp = 20 log10(p/p0), whereas electrical power levels use Lp = 10 log10(P/P0). Thus a 20‑decibel increase corresponds to a ten‑fold increase in sound pressure or a hundred‑fold increase in power. In audio contexts, a guitar amp outputting 20 dB above the loudness threshold is more than a mild annoyance and may be perceived as a slight hum. In telecommunications, a 20‑dB gain in a radio amplifier dramatically improves signal reception. In environmental noise monitoring, a 20‑dB rise at a window can mean a significant shift from a quiet office to a moderately noisy street.

Because the decibel scale is logarithmic, it allows concise representation of huge dynamic ranges, from the quietest background noise to the loudest explosions. The 20‑dB step is frequently used as a standard reference for comparing relative sound levels, identifying changes in acoustic environments, and adjusting electronic amplifier settings.