Sound, fundamental to our environment, reaches our ears as vibrations traveling through a medium like air. These vibrations possess distinct characteristics, including frequency. Measured in Hertz (Hz), frequency refers to the number of sound wave cycles per second. Humans perceive only a specific portion of the vast spectrum of frequencies.
The Lowest Audible Frequency
The lowest frequency a human can perceive is around 20 Hz, though some individuals might detect sounds as low as 12 Hz under ideal laboratory conditions. At this lower limit, sound is experienced less as a distinct tone and more as a physical sensation, such as a rumble or vibration. The ear’s sensitivity decreases significantly as frequencies drop, meaning low-frequency sound requires substantial sound pressure to be perceived.
Sounds at or near 20 Hz are characterized by their low pitch, referred to as “sub-bass” or “bass” sounds. Examples of natural occurrences include the deep rumble of distant thunder or powerful vibrations from large waterfalls. In music, bass notes from instruments like large pipe organs can approach this lower threshold. Specialized audio equipment, such as subwoofers, is necessary to reproduce sounds at 20 Hz effectively, as most standard speakers cannot generate such low frequencies.
Individual Hearing Variations
The 20 Hz figure represents an average, and an individual’s lowest frequency perception can vary. A primary factor influencing this range is age, as the ability to hear both high and low frequencies can diminish over time. While high-frequency hearing loss is more commonly discussed with aging, the lower threshold can also be affected.
Beyond age, other elements can influence an individual’s hearing range. Prolonged exposure to loud noise can damage inner ear structures, potentially impacting the ability to perceive sounds across the frequency spectrum. Certain medical conditions (like Meniere’s disease), genetic predispositions, some medications, or viral infections can also alter an individual’s low-frequency hearing.
Sounds Below Our Range
Frequencies below the human hearing threshold of 20 Hz are known as infrasound. Humans cannot hear infrasound because our auditory system is not designed to efficiently process these long wavelengths and slow vibrations. Despite being inaudible, powerful infrasound can be perceived as vibrations throughout the body or may cause physiological effects.
Natural sources generate infrasound, including large-scale phenomena like earthquakes, volcanic eruptions, avalanches, and severe weather such as storms. The powerful interactions of ocean waves can also produce infrasound vibrations. Certain animals, like elephants and whales, utilize infrasound for long-distance communication, demonstrating their ability to perceive frequencies beyond human range. Artificial sources of infrasound include large machinery, wind turbines, and even sonic booms. While not heard, strong infrasound exposure has been linked to feelings of unease, pressure sensations, or even disrupted sleep in some individuals.