Simple Explanation

Sound that’s too deep or low in frequency for humans to hear—below 20 Hz.

Concise Technical Definition

Refers to acoustic waves or vibrations with frequencies below the audible threshold of human hearing, typically under 20 Hz.

Layman-Friendly Analogy

Like an earthquake rumble you can feel but not hear—it’s sound, just too low for your ears to pick up.

Industry Usage Summary

Infrasonic frequencies are filtered out in audio systems using infrasonic filters to remove unwanted low-end noise like turntable rumble; the term is often confused with "subsonic," which technically refers to speed, not frequency.

Engineering Shortcut

Frequencies < 20 Hz; filtered to reduce inaudible rumble.

Full Technical Explanation

Infrasonic describes sound waves with frequencies below 20 Hz—below the threshold of normal human hearing. While these frequencies are not audibly perceived, they can often be felt as vibrations. In audio systems, infrasonic content typically originates from mechanical noise, subwoofer artifacts, or environmental sources like HVAC systems. Since such low frequencies can waste amplifier power or cause speaker damage without contributing to perceived audio quality, many systems include infrasonic (low-cut or high-pass) filters to remove them. The term "subsonic" is frequently used interchangeably but inaccurately; subsonic technically relates to the speed of sound, not frequency.