Simple Explanation

How loud or soft a sound feels to your ears—not just the volume, but how your brain hears it.

Concise Technical Definition

The perceived intensity of sound, measured in phons, and influenced by frequency as well as sound pressure level (SPL); not a linear function of amplitude.

Layman-Friendly Analogy

Like how a whisper can seem loud in a quiet room or how bass feels stronger even if it’s not actually louder—it’s about how your ears feel the sound.

Industry Usage Summary

On preamps or receivers, a loudness control boosts bass and sometimes treble at lower volumes to match how human hearing perceives sound at different levels, based on the Fletcher-Munson curves (equal loudness contours).

Engineering Shortcut

Perceived volume; not just SPL—depends on frequency and level.

Full Technical Explanation

Loudness is the perceived strength or intensity of sound by the human ear, which doesn’t respond equally to all frequencies. At low volumes, the ear is less sensitive to low and high frequencies, so sounds can seem "thin" or lacking in depth. To compensate, audio systems may use a loudness control, which boosts the low and high frequencies at lower volume levels to create a more natural listening experience. Scientifically, loudness is measured in phons, a unit that equates a given SPL at a specific frequency to how loud it seems compared to a 1 kHz tone. This relationship is mapped by the Fletcher-Munson curves, which show how our hearing sensitivity changes with both frequency and amplitude. Understanding loudness is essential in audio mixing, playback system design, and sound perception research.