Explore the fascinating world of human hearing, from the frequencies we can perceive to the amazing abilities of animals. Discover how technology helps us hear better and how sound is used in various applications.
The audible range of sound for human beings extends from about 20 Hz to 20,000 Hz (one Hz = one cycle/s).
Children under the age of five and some animals, such as dogs can hear up to 25 kHz (1 kHz = 1000 Hz).
As people grow older their ears become less sensitive to higher frequencies. This is why elderly people often have difficulty hearing high-pitched sounds.
The human ear is most sensitive to frequencies between 1000 Hz to 4000 Hz, which includes the range of human speech.
Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.
If we could hear infrasound we would hear the vibrations of a pendulum just as we hear the vibrations of the wings of a bee.
Earthquakes produce low-frequency infrasound before the main shock waves begin which possibly alert the animals. This is why some animals get disturbed before earthquakes.
Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.
Ultrasound is produced by animals such as dolphins, bats and porpoises for navigation and hunting purposes.
Moths of certain families have very sensitive hearing equipment. These moths can hear the high frequency squeaks of the bat and know when a bat is flying nearby, and are able to escape capture.
Rats also play games by producing ultrasound that humans cannot hear.
People with hearing loss may need a hearing aid. A hearing aid is an electronic, battery operated device.
The hearing aid receives sound through a microphone. The microphone converts the sound waves to electrical signals.
These electrical signals are amplified by an amplifier. The amplified electrical signals are given to a speaker of the hearing aid.
The speaker converts the amplified electrical signal to sound and sends to the ear for clear hearing.
Metallic components are generally used in construction of big structures like buildings, bridges, machines and also scientific equipment.
The cracks or holes inside the metal blocks, which are invisible from outside reduces the strength of the structure.
Ultrasonic waves are allowed to pass through the metal block and detectors are used to detect the transmitted waves.
If there is even a small defect, the ultrasound gets reflected back indicating the presence of the flaw or defect.
Other Applications of Ultrasound:
• Medical Imaging: Used to create images of internal body structures
• Cleaning: Ultrasonic cleaners remove dirt and contaminants
• Sonar: Ships and submarines use ultrasound for navigation
• Thickness Measurement: Measuring thickness of materials without damaging them
Understanding the Science Behind Sound Frequencies
Sound is a mechanical wave that travels through air, water, or solid materials by vibrating particles.
Frequency (Hz) determines the pitch - higher frequencies produce higher pitches, lower frequencies produce lower pitches.
The human ear contains specialized structures that convert sound waves into electrical signals the brain can interpret.
Outer ear collects sound waves and funnels them into the ear canal toward the eardrum.
Middle ear amplifies vibrations through three tiny bones: hammer, anvil, and stirrup.
Inner ear contains the cochlea with thousands of hair cells that convert vibrations to nerve signals.
Wavelength and frequency have an inverse relationship - as frequency increases, wavelength decreases.
Sound speed in air is approximately 343 m/s at room temperature and varies with medium density.
Amplitude determines loudness (decibels), while frequency determines pitch (Hz).
Animals like bats and dolphins emit high-frequency sounds and analyze returning echoes.
Time delay between call and echo reveals distance to objects in the environment.
Echo characteristics provide information about object size, texture, density, and movement.
Digital signal processing allows modern hearing aids to filter noise and enhance speech frequencies.
Directional microphones focus on sounds from specific directions while reducing background noise.
Frequency shaping amplifies specific frequency ranges based on individual hearing loss patterns.
Medical ultrasound uses frequencies between 1-20 MHz to create images of internal body structures.
Industrial testing employs ultrasound to detect flaws in materials without causing damage.
Sonar technology uses sound waves for underwater navigation, mapping, and object detection.