Sound waves are vibrations that travel through a medium, such as air or water, carrying energy. These vibrations create patterns of pressure changes that our ears can detect and our brains interpret as sound. Understanding these waves, particularly their frequency, is fundamental to comprehending sound.
The Hertz: The Standard Unit
The metric unit used to measure the frequency of sound waves is the Hertz (Hz). Frequency quantifies how many complete cycles or oscillations of a wave occur within one second. One Hertz is one cycle per second. For example, if a sound wave completes 100 full vibrations in a single second, its frequency is 100 Hz.
This concept can be compared to a pendulum swinging back and forth; if it completes one full swing (forward and back to its starting point) every second, its frequency is 1 Hz. The Hertz is part of the International System of Units (SI), which provides a standardized framework for measurements across scientific and everyday applications worldwide.
Frequency and How We Hear
The frequency of a sound wave directly influences how humans perceive its pitch. Higher frequencies correspond to sounds that we hear as higher-pitched, like the high notes on a flute. Conversely, lower frequencies produce sounds that are perceived as lower-pitched, similar to the deep rumble of a drum.
The human ear can perceive frequencies from about 20 Hertz (Hz) to 20,000 Hertz (20 kHz). Sounds below 20 Hz are often felt as vibrations rather than heard, while sounds above 20 kHz become inaudible. This range varies among individuals and often decreases with age, particularly at the higher end.
Beyond Human Hearing
While humans perceive a specific range of frequencies, sound waves exist far beyond what our ears can detect. Frequencies below the human hearing threshold, less than 20 Hz, are known as infrasound. This type of sound can be generated by various natural phenomena, such as earthquakes, large storms, or even the movements of large animals. Some animals, including elephants, utilize infrasound for long-distance communication, allowing them to communicate across vast areas.
On the other end of the spectrum, frequencies above 20,000 Hz are referred to as ultrasound. Humans cannot hear these high-frequency sounds, but many animals, like bats and dolphins, use ultrasound for echolocation to navigate and locate prey. Ultrasound also has numerous practical applications, including medical imaging, where it is used to visualize internal body structures without invasive procedures. It is also employed in sonar systems for underwater navigation and mapping.