noiselevel

Noise level is a measure of the loudness of sound in an environment, typically quantified as sound pressure level in decibels (dB). Because sound pressure scales logarithmically, a small change in dB represents a large difference in acoustic energy; for example, a 10 dB increase is generally perceived as about twice as loud, while a 20 dB increase is perceived as roughly four times as loud.

Common measurement approaches use frequency weighting to reflect human hearing. The A-weighted scale (dBA) is widely used for general noise assessment because it de-emphasizes low and very high frequencies to resemble average human sensitivity. Other metrics include unweighted decibels (dB), C-weighted (dBC) for peak or low-frequency content, and multi-parameter indicators such as Leq (equivalent continuous sound level), Lmax (maximum level), and Lmin (minimum level). In environmental noise assessments, Lden (day-evening-night level) aggregates levels with penalties for evening and night to reflect differing human tolerance.

Measurement is performed with sound level meters or personal dosimeters, calibrated against a reference of 20 micropascals at 1 kHz. Standards guide methods, accuracy, and reporting, with regions adopting ISO 1996-1, IEC 61672, or ANSI S1.4 family standards.

Applications span environmental noise control, occupational safety, product testing, and compliance labeling for consumer devices. Typical exposure levels range from quiet rooms (30–40 dBA) to busy streets (70–85 dBA) to industrial settings (often above 85 dBA). Limitations include that decibel scales are not a direct measure of subjective loudness and that weighting schemes approximate perception rather than exact experience across all conditions.