infrasonic

This term describes a specific acoustic range that exists beyond the threshold of human perception. It is primarily used in scientific, geological, and biological contexts to describe low-frequency vibrations that can travel vast distances through the earth or atmosphere without significant attenuation.

Because it refers to a technical physical property, the word carries a neutral, clinical connotation. It is frequently contrasted with ultrasonic (above human hearing) and sonic (within human hearing) to categorize the spectrum of sound waves based on their frequency.