What is the physical unit most commonly used to describe sound levels?

• A. Decibel
• B. Bel
• C. Hertz
• D. Watt

Answer: (A)

Sound levels are described with a logarithmic unit because our ears perceive intensity logarithmically, and the decibel provides that scale. The decibel is the commonly used unit to express sound pressure level or sound intensity relative to a reference, making it practical to cover the wide range of sounds we encounter. In practice, measurements are often given as dB SPL, using 20 micropascals as the reference pressure for air. This is why decibels are the standard choice for describing how loud something is.

The other options don’t fit as well: a bel is the larger, rarely-used precursor to the decibel; Hertz measures frequency (cycles per second) rather than level; Watt measures power, not a perceptual level of sound.