Subfrequency

Subfrequency is a term used in acoustics, signal processing, and related fields to denote a frequency range that lies below a defined threshold. In many contexts the threshold is the lower bound of human auditory perception, about 20 Hz, but in technical analyses it may refer to frequencies below a user-specified cutoff. Subfrequency components can be significant for the perception of bass, room acoustics, and certain physical processes, even when they are not individually audible.

In audio and music production, subfrequency typically refers to the bass and sub-bass portion of the spectrum, roughly from 20 Hz to 60–80 Hz depending on the system. Subwoofers are designed to reproduce these frequencies to provide tactile and perceptual bass. Subfrequency content can influence perceived loudness, tightness, and spatial impression even when higher frequencies carry the main melodic content.

In signal analysis and instrumentation, subfrequency bands are isolated with low-pass filters or by methods such as Fourier analysis, wavelets, or decimation. Subfrequency measurements are common in seismology, vibration analysis, and structural health monitoring to study phenomena like infrasonic waves, ambient vibrations, or resonance modes.

Challenges include environmental noise, room modes, and equipment sensitivity. Because subfrequencies have long wavelengths, they interact with large spaces and structures in complex ways, making accurate measurement and reproduction technically demanding.

See also: infrasonic, sub-bass, low frequency, Fourier transform, filtering, bass, subwoofer.