Sound travels as waves, and the frequency of these waves is measured in Hertz (Hz). One Hertz represents one cycle per second. In the context of hearing, frequency determines the pitch of a sound: lower frequencies correspond to deeper sounds, while higher frequencies correspond to sharper ones.
The Standard Human Hearing Range
For a healthy young adult, the typical range of human hearing spans from approximately 20 Hz to 20,000 Hz, also known as 20 kHz. Sounds below 20 Hz are generally too low to be consciously heard, while those above 20,000 Hz are too high.
Low frequencies, such as 20 Hz, are perceived as deep bass tones, similar to the lowest notes on a large pipe organ or the rumble of distant thunder. Conversely, high frequencies, like 20,000 Hz, are heard as piercing, high-pitched sounds, comparable to a mosquito’s buzz or the highest notes produced by a tiny bell. The human auditory system is most sensitive to frequencies between 2,000 and 5,000 Hz, which includes most speech frequencies.
Factors Influencing Hearing Range
Individual hearing capacity varies due to several factors. Age is a primary influence, as the ability to hear higher frequencies naturally diminishes over time, a condition known as presbycusis. For example, while someone in their twenties might hear up to 17,000 Hz, an individual in their fifties may find sounds above 12,000 Hz imperceptible. This age-related decline typically begins around age eight, with a gradual reduction in the upper frequency limit.
Exposure to loud noise is another significant factor. Prolonged or intense exposure to sounds exceeding 85 decibels can damage the delicate hair cells in the inner ear. These hair cells are responsible for transmitting sound vibrations to the brain, and unlike other cells, they do not regenerate once damaged. This damage can lead to noise-induced hearing loss, reducing the range of frequencies an individual can hear.
Other less common factors can also affect hearing, including genetics, certain medical conditions, and some medications. Conditions like ear infections or Meniere’s disease, for instance, can impact hearing ability.
Beyond the Range and Protecting Your Hearing
Sounds exist beyond the human hearing range, categorized as infrasound and ultrasound. Infrasound refers to frequencies below 20 Hz, which are typically inaudible to humans but can sometimes be felt as vibrations. Natural sources of infrasound include earthquakes, volcanoes, and ocean waves. Some animals, such as elephants, use infrasound for long-distance communication.
Conversely, ultrasound refers to frequencies above 20,000 Hz. Animals like bats and dolphins use ultrasound for echolocation, navigating and hunting by emitting high-frequency sounds and interpreting the echoes. In medical applications, ultrasound is used to create images of internal body structures, such as in fetal scanning or examining internal organs.
Protecting your hearing preserves your auditory range. Avoiding prolonged exposure to loud noises is a key preventive measure; if a sound is so loud that you need to shout to be heard, it is likely damaging your ears. Using hearing protection, such as earplugs or earmuffs, is advisable in noisy environments like concerts or when operating loud machinery. Being mindful of headphone volume and taking breaks from listening can help reduce the risk of noise-induced hearing loss.