Inaudible Audible Sound - Frequency Range and Vibration

Edited By Vishal kumar | Updated on Jul 02, 2025 05:04 PM IST

A musical sound is pleasing to listen while noise is not. The meaning of audible is “Loud enough to be heard or able to be heard”. A sound is energy is vibrations made in the air, which are audible in living creatures. According to frequency, sound can be classified into audible or inaudible. In this article, we will discuss the concept of Audible and Inaudible sound, along with examples for better understanding.

This Story also Contains

What is Audible Sound?
What is Inaudible Sound?
Difference between Audible Sound and Inaudible Sound
Applications of Audible Sound
Applications of Inaudible Sound

Inaudible Audible Sound - Frequency Range and Vibration

What is Audible Sound?

The sound waves ranging between 20Hz and 20 KHz are called Audible sound. SI unit of frequency is the hertz (Hz).

Frequency of Audible sound:

An audio frequency or audible frequency is a repeated vibration whose frequency is in the band audible to the common man, the human hearing range.

Low-frequency sounds (around 20 Hz ) are recognized as deep or bass sounds.
High-frequency sounds (close to $20,000 \mathrm{~Hz}$ ) are recognized as high-pitched sounds.

Human Hearing:

Hearing is determined by how the ear organ is formed, the ear canal, drum, and cochlea. According to the theories when sound waves get in touch with the eardrum, they make vibrations and these vibrations are converted into sound by the brain.

The 'normal' hearing frequency range of a fit young person is about 20 to 20,000Hz. However, a 'normal' audible range for noise or loudness is from 0 to 180dB, anything over 85dB is considered damaging, so we should try not to go there.
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Examples of Audible Sound:

Loud speech, songs, horns, and mechanical noises, squeaking or cracking noises, voices and shouts, music, birds singing, and a barking of a dog are all examples of sound that one can hear as an auditory sensation.

What is Inaudible Sound?

The sound that falls outside the range of human hearing is called an inaudible sound. The frequencies occupying below 20Hz and those occupying above 20 kHz cannot be recognized by the human ears. Therefore these frequencies are called audible sounds.

Frequencies lower than 20Hz are referred to as Infrasonic Sound. These frequencies are felt as a vibration. Example- Earthquake, sounds produced by some animals like elephants or whales for long-distance communication.
Frequencies higher than 20KHz are referred to as Ultrasonic Sound. Humans are unable to detect these sounds but they can be recognized using special equipment. Example- Sound waves used in Pest control, and medical ultrasound imaging.

Example of Inaudible Sound

The hearing range of animals like dogs can recognize the frequencies lying above 20 kHz. Therefore dogs are trained in police forces with the help of warble (Whistle) which serve as a source of frequencies greater than 20 kHz.

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Difference between Audible Sound and Inaudible Sound

Below table shows the key differences between Audible Sound and Inaudible Sound for easy understanding:

Audible Sounds	Inaudible sounds
Audible sounds are sounds of frequency that are audible to the human ear	Inaudible sounds are sounds of frequency that are not audible to the human ear
The frequency of audible sound is usually 20 Hz -20 KHz.	The frequency of inaudible sound is usually less than 20 Hz and above than 20 KHz.
It can be heard by humans and animals	It can be heard by only some animal life like dolphin
Example: sounds with frequency from 20 Hz to 20, 000 Hz	Example: Sounds with frequency less than 20 Hz or more than 20,000 Hz

Applications of Audible Sound

Communication: Human speech and music are fundamental to communication.
Entertainment: Music, movies, radio, and other items used sound within the audible frequency.
Safety: Sounds like bells and horns call our attention to risks that are present like fire or thief.

Applications of Inaudible Sound

Ultrasound: Applied in medicine for full-body scans without surgery, for instance, pregnancy scans.
Infrasound: Used for purposes of identifying natural phenomena such as an earthquake or tsunami.
Animal Communication: A lot of animals use low-frequency for communication to find their way like bats and dolphins.

Frequently Asked Questions (FAQs)

1. What is human ear decibel range?

Most speech sounds vary from 30 to 70 decibels, the right human hearing frequency vary that describes mild-to-moderate hearing disorder.

2. How much Hertz human can hear?/What is the audio frequency range of humans?

Humans will hear about/the audible sound range for humans is/audible get human range of 20 Hz to 20kHz.

3. Define intensity of sound?

The intensity of sound at a point is the time rate of flow of sound energy passing normally through a unit area at the point. Its unit is the joule per sec. sq. m (J/s.m²) or watt per square metre (W/m²).

4. Which quantity out of frequency and amplitude determines the pitch of the sound? Or Which out of pitch and frequency is a measurable quantity?

The frequency of sound determines its pitch. A high pitched or shrill sound is produced by a body vibrating with a high frequency and a low pitched or flat sound is produced by a body vibrating with a low frequency.

Frequency is a measurable quantity whereas pitch is not a measurable quantity.

5. Give reason: The notes of sitar and a guitar sound different even if they have the same loudness and the pitch.

The quality or timbre of the sound of a sitar is different from that of a guitar. The number of overtones or partials present and their relative intensities determine the quality or timbre of the sound of a musical instrument. Therefore, even if the pitch and the loudness are the same, the notes of a sitar and guitar sound different.

6. How is the audible frequency range test done?

The frequency range is tested using frequency counter or spectrum analyzer.

7. Why can't humans hear all sound frequencies?

Humans can't hear all sound frequencies because our ears have physical limitations. The structures in our inner ear, particularly the cochlea and its hair cells, are optimized to respond to a specific range of frequencies. Sounds outside this range don't effectively stimulate these structures, making them inaudible to us.

8. What is the typical human hearing range?

The typical human hearing range is approximately 20 Hz to 20,000 Hz (20 kHz). This range can vary slightly between individuals and tends to decrease with age, especially at higher frequencies.

9. What is infrasound?

Infrasound refers to sound waves with frequencies below the lower limit of human hearing, which is typically 20 Hz. These low-frequency sounds are inaudible to humans but can be detected by some animals and specialized equipment.

10. What is ultrasound?

Ultrasound refers to sound waves with frequencies above the upper limit of human hearing, which is typically 20,000 Hz (20 kHz). These high-frequency sounds are inaudible to humans but can be heard by some animals and are used in various technological applications.

11. How do animals like bats and dolphins use ultrasound?

Bats and dolphins use ultrasound for echolocation. They emit high-frequency sound waves that bounce off objects in their environment. By analyzing the echoes, these animals can determine the location, size, and movement of objects around them, allowing them to navigate and hunt effectively.

12. Why do some people claim to hear sounds that others can't?

Some people may have a slightly wider hearing range or increased sensitivity to certain frequencies. Additionally, factors like age, previous noise exposure, and individual variations in ear structure can affect hearing abilities. In some cases, people may also experience tinnitus, which can create the perception of sounds that aren't present in the environment.

13. Can infrasound or ultrasound be dangerous to humans?

While not directly audible, both infrasound and ultrasound can potentially affect humans. Prolonged exposure to high-intensity infrasound can cause feelings of discomfort, disorientation, and even physical symptoms. High-intensity ultrasound can heat and damage tissues, which is why it's carefully controlled in medical applications.

14. How does age affect our ability to hear high-frequency sounds?

As we age, we typically experience a gradual loss of hearing, especially at higher frequencies. This condition, known as presbycusis, occurs due to the natural deterioration of hair cells in the inner ear. It's why older adults often have difficulty hearing high-pitched sounds or understanding speech in noisy environments.

15. What is the relationship between frequency and wavelength in sound waves?

Frequency and wavelength in sound waves are inversely related. As frequency increases, wavelength decreases, and vice versa. This relationship is described by the equation: wave speed = frequency × wavelength. Since the speed of sound is relatively constant in a given medium, higher frequency sounds have shorter wavelengths, and lower frequency sounds have longer wavelengths.

16. How do musical instruments produce different frequencies?

Musical instruments produce different frequencies through various mechanisms. String instruments change frequency by altering string length, tension, or thickness. Wind instruments use different lengths of air columns and changes in embouchure (mouth position). Percussion instruments often use different sizes or tensions in vibrating surfaces. The specific design of each instrument determines its range of producible frequencies.

17. How does the medium affect sound propagation?

The medium through which sound travels significantly affects its propagation. Sound waves travel faster in denser mediums. For example, sound travels faster in water than in air, and faster in solids than in liquids. The medium also affects how far sound can travel and how much it's attenuated (reduced in intensity) over distance.

18. What is resonance, and how does it relate to sound frequencies?

Resonance is the tendency of a system to oscillate with greater amplitude at certain frequencies, known as resonant frequencies. In the context of sound, when an object is exposed to sound waves at its natural frequency, it will vibrate more readily, potentially amplifying the sound. This principle is used in musical instruments and can also explain why certain structures might vibrate in response to specific sound frequencies.

19. What is the Doppler effect, and how does it relate to sound frequency?

The Doppler effect is the change in frequency of a wave for an observer moving relative to its source. For sound, this means that as a source of sound approaches an observer, the perceived frequency increases (higher pitch), and as it moves away, the frequency decreases (lower pitch). This effect occurs because the motion of the source compresses or expands the wavelengths relative to the observer.

20. How does the shape of the ear affect our ability to localize sound?

The shape of the outer ear (pinna) plays a crucial role in sound localization. Its complex folds and ridges modify incoming sound waves differently depending on the direction of the sound source. These modifications, along with the time difference between when sound reaches each ear and the intensity difference between ears, provide cues that our brain uses to determine the location of a sound source in three-dimensional space.

21. How do harmonics relate to the fundamental frequency of a sound?

Harmonics are integer multiples of the fundamental frequency of a sound. When an object vibrates, it often produces not just the fundamental frequency but also these harmonic frequencies. The presence and strength of different harmonics contribute to the timbre or quality of a sound, allowing us to distinguish between different instruments or voices even when they're playing the same note (fundamental frequency).

22. What is the difference between forced and natural vibrations?

Forced vibrations occur when an object is made to vibrate by an external periodic force. The frequency of these vibrations matches the frequency of the applied force, regardless of the object's natural frequency. Natural vibrations, on the other hand, occur at an object's natural frequency when it's disturbed and left to vibrate freely. The frequency of natural vibrations depends on the object's physical properties like mass, stiffness, and shape.

23. What is acoustic impedance, and how does it affect sound transmission?

Acoustic impedance is a measure of how much a medium resists the flow of sound energy. It's determined by the density of the medium and the speed of sound in that medium. When sound waves encounter a boundary between media with different acoustic impedances (like air and water), part of the sound is reflected and part is transmitted. The greater the difference in impedance, the more sound is reflected. This principle is important in understanding sound transmission between different materials and in designing acoustic treatments.

24. How do standing waves relate to room acoustics and sound frequencies?

Standing waves are patterns of sound waves that occur in enclosed spaces when reflected waves interfere with incident waves. In room acoustics, standing waves can create areas of increased and decreased sound intensity at specific frequencies, known as room modes. These modes depend on the room's dimensions and can lead to uneven frequency response in different parts of the room. Understanding and managing standing waves is crucial in acoustic design for spaces like recording studios and concert halls.

25. What is the role of the basilar membrane in frequency discrimination?

The basilar membrane in the cochlea plays a crucial role in frequency discrimination. It's structured so that different frequencies cause maximum vibration at different points along its length. High frequencies cause maximum vibration near the base of the cochlea, while low frequencies cause maximum vibration near the apex. This tonotopic organization allows the auditory system to separate and analyze different frequency components of complex sounds, forming the basis for our ability to distinguish different pitches.

26. What is the significance of the Nyquist frequency in digital audio recording?

The Nyquist frequency is half the sampling rate of a digital system and represents the highest frequency that can be accurately represented in digital form. According to the Nyquist-Shannon sampling theorem, to accurately capture a sound, the sampling rate must be at least twice the highest frequency component of the sound. This concept is crucial in digital audio recording to avoid aliasing, where higher frequencies can be misrepresented as lower frequencies, causing distortion.

27. How do different materials absorb or reflect different sound frequencies?

Different materials interact with sound waves differently based on their physical properties and the frequency of the sound. Generally, porous materials like foam or fiberglass are more effective at absorbing high-frequency sounds, while denser, more massive materials are better at blocking low-frequency sounds. The thickness and structure of a material also play a role. For example, resonant absorbers can be designed to target specific frequency ranges. Understanding these properties is crucial in acoustic design and soundproofing.

28. How does the concept of beats relate to slightly different frequencies?

Beats are periodic variations in amplitude that occur when two sounds with slightly different frequencies interfere with each other. The beat frequency is equal to the difference between the two original frequencies. For example, if two sounds with frequencies of 440 Hz and 444 Hz are played together, beats will be heard at a frequency of 4 Hz. This phenomenon is used in tuning musical instruments and demonstrates the wave nature of sound.

29. What is the difference between frequency modulation (FM) and amplitude modulation (AM) in sound?

Frequency modulation (FM) and amplitude modulation (AM) are two ways of encoding information in a sound wave. In FM, the frequency of a carrier wave is varied to encode information, while the amplitude remains constant. In AM, the amplitude of the carrier wave is varied while the frequency remains constant. FM generally provides better sound quality and is less susceptible to noise, which is why it's often preferred for high-fidelity audio transmission.

30. How does the speed of sound affect its frequency?

The speed of sound in a medium does not directly affect its frequency. Frequency is determined by the source of the sound and remains constant as the sound travels through different media. However, the speed of sound does affect the wavelength of the sound wave. As the speed changes (e.g., moving from air to water), the wavelength changes proportionally to maintain the same frequency, following the relationship: speed = frequency × wavelength.

31. What is the concept of critical frequency in room acoustics?

In room acoustics, the critical frequency (or Schroeder frequency) is the point above which the sound field in a room is considered diffuse. Below this frequency, individual room modes (standing waves) dominate the acoustic response. Above it, there are enough modes overlapping that the sound field becomes more uniform. The critical frequency depends on the room's size and reverberation time. Understanding this concept is crucial for acoustic treatment and speaker placement in rooms.

32. What is the role of formants in speech and vowel recognition?

Formants are concentrations of acoustic energy around particular frequencies in the speech spectrum. They result from the resonant frequencies of the vocal tract and are crucial for vowel recognition. Different vowel sounds are characterized by different formant patterns, typically involving the first two or three formants. The ability to perceive and distinguish these formant patterns allows us to differentiate between vowel sounds, even when the fundamental frequency (pitch) of the voice changes.

33. How do noise-cancelling headphones work with different frequencies?

Noise-cancelling headphones use active noise control to reduce unwanted ambient sounds. They work by using microphones to detect incoming sound waves, then generating sound waves of the same amplitude but with inverted phase (anti-noise) to cancel out the unwanted noise. This technology is most effective for lower frequency sounds, which have longer wavelengths and are more predictable. Higher frequency sounds are more challenging to cancel due to their shorter wavelengths and more complex patterns.

34. What is the difference between frequency and pitch?

Frequency is a physical property of a sound wave, measured in Hertz (Hz), which represents the number of wave cycles per second. Pitch, on the other hand, is the psychological perception of frequency. While frequency and pitch are closely related, they are not identical. Our perception of pitch can be influenced by factors other than frequency, such as loudness and timbre.

35. How do animals with different hearing ranges communicate?

Animals with different hearing ranges have evolved various communication strategies. Some use vocalizations within their species' hearing range. Others may use visual, chemical, or tactile signals. For example, elephants can communicate using low-frequency infrasound that travels long distances, while bats use high-frequency ultrasound for both communication and echolocation. Some species may also be sensitive to vibrations or electric fields for communication.

36. What is the concept of critical bands in hearing?

Critical bands are a psychoacoustic concept related to how our auditory system processes different frequencies. The ear doesn't perceive frequencies as a continuum but rather groups them into critical bands. Within a critical band, frequencies are processed together and can mask each other. This concept is important in understanding how we perceive complex sounds and in applications like audio compression algorithms.

37. What is the Fletcher-Munson curve, and how does it relate to perceived loudness across frequencies?

The Fletcher-Munson curve, also known as equal-loudness contours, illustrates how the perceived loudness of a sound varies with frequency. These curves show that human hearing is not equally sensitive to all frequencies at the same sound pressure level. We are most sensitive to frequencies in the 2-5 kHz range and less sensitive to very low and very high frequencies. This means that to be perceived as equally loud, low and high-frequency sounds need to have higher intensity than mid-range frequencies.

38. How does sound intensity relate to frequency?

Sound intensity, which is related to the amplitude of sound waves, doesn't inherently depend on frequency. However, our perception of loudness (which is related to intensity) does vary with frequency, as illustrated by the Fletcher-Munson curves. Additionally, in practical situations, higher frequency sounds tend to attenuate more quickly over distance than lower frequency sounds, which can affect perceived intensity at a distance from the source.

39. What is the cocktail party effect, and how does it relate to our ability to focus on specific frequencies?

The cocktail party effect refers to the brain's ability to focus on a specific voice or sound source in a noisy environment, effectively filtering out other sounds. This phenomenon demonstrates our auditory system's capacity for selective attention and frequency discrimination. It involves complex processing in the brain, including the ability to separate and analyze different frequency components of sounds, as well as using spatial cues to distinguish between sound sources.

40. How do bone conduction headphones work, and why can they transmit sounds outside the typical air conduction range?

Bone conduction headphones transmit sound vibrations directly through the bones of the skull to the inner ear, bypassing the outer and middle ear. This technology can be effective for people with certain types of hearing loss that affect the outer or middle ear. Bone conduction can transmit a wider range of frequencies than air conduction, including some frequencies outside the typical human hearing range, because it doesn't rely on the same physical limitations of the ear canal and eardrum.

41. How does the concept of masking apply to different sound frequencies?

Masking occurs when the perception of one sound is affected by the presence of another sound. It's particularly relevant when considering different frequencies. Lower frequency sounds tend to mask higher frequency sounds more effectively than vice versa. This is partly due to how the basilar membrane responds to different frequencies. Masking can occur within critical bands (frequency masking) or over time (temporal masking). Understanding masking is crucial in fields like audio compression and acoustic design.

42. What is the relationship between frequency and energy in sound waves?

The energy of a sound wave is directly proportional to its frequency. Higher frequency waves have shorter wavelengths and oscillate more rapidly, carrying more energy per unit time than lower frequency waves of the same amplitude. This relationship is described by the equation E = hf, where E is energy, h is Planck's constant, and f is frequency. This concept explains why high-frequency sounds can be more damaging to hearing at the same amplitude as lower frequency sounds.

43. How do phase differences between frequencies affect sound perception?

Phase differences between frequency components can significantly affect how we perceive sound. When multiple frequencies are in phase, they reinforce each other, potentially creating a stronger or clearer sound. Out-of-phase components can lead to cancellations or a perceived change in the timbre of the sound. Our auditory system is more sensitive to phase differences at lower frequencies. Phase relationships are particularly important in stereo sound reproduction and in understanding how we localize sounds.

44. How does the concept of frequency response apply to audio equipment?

Frequency response in audio equipment refers to the range of frequencies that a device can reproduce and how evenly it reproduces them. It's typically represented as a graph showing the output level across the audible frequency spectrum. An ideal frequency response would be flat, meaning all frequencies are reproduced at the same relative level. In practice, most audio equipment has some variation in response across frequencies. Understanding frequency response is crucial for selecting and using audio equipment for accurate sound reproduction.

45. What is aliasing in digital audio, and how does it relate to frequency?

Aliasing in digital audio occurs when frequencies above the Nyquist frequency (half the sampling rate) are incorrectly represented as lower frequencies. This happens because the sampling rate is too low to accurately capture the high-frequency content. Aliasing can introduce distortion and unwanted artifacts in the audio. To prevent aliasing, audio signals are typically filtered to remove frequencies above the Nyquist frequency before analog-to-digital conversion.

46. How do combination tones arise from multiple frequencies?

Combination tones are additional tones perceived when two or more tones are played simultaneously. They include sum tones (at the sum of the original frequencies) and difference tones (at the difference of the frequencies). These tones