What is Sound?
What we hear is nothing but sound, right? That’s it? Is it that simple? Physicists sometimes tend to complicate things. They define sound as a vibration that propagates the mechanical wave of displacement and pressure, through a medium can be of any matter. Sound just got complicated!
What we hear is the effect produced because of the to-and-fro motion of the particles from any medium. The to-and-fro motion is referred to as vibration. Sound moves through a medium by alternately expanding and contracting the parts of the medium which it is traveling through. This compression and expansion create a minute difference in pressure that we perceive as sound. Thereby, it is a mechanical wave of displacement and pressure. In other words, the sound is the thin line between Music sound and Noise.
In human psychology and physiology, the sound is the reception of such waves and perception by the brain.
Types of Sound
Sounds are of various types, based on the pitch, loudness, frequency, and amplitude of the sound wave, but not all these please our hearing sense. Based on whether we like it or not, the types of sound are widely classified into noise and music. Music is what pleases our hearing sense. It depends on various factors and varies from person to person. On the other side, the definition of noise is simply hazy, which is not clear. The boundary that separates the musical sound from noise is blurry. Music to someone can be noise to someone else.
Acoustics of Sound
Acoustics is referred to as an interdisciplinary science, deals with the study of mechanical waves in solids, liquids, gases, together with vibration, sound, ultrasound, infrasound. One of the scientists who work in the acoustics field is referred to acoustician, whereas someone working in the acoustical engineering field may be called an acoustical engineer. On the other side, an audio engineer is concerned with the recording, mixing, manipulation, and reproduction of sound.
Applications of acoustics are found mostly in every aspect of modern society; subdisciplines include audio signal processing, aeroacoustics, architectural acoustics, electro-acoustics, bioacoustics, environmental noise, musical acoustics, psychoacoustics, noise control, ultrasound, vibration, speech, and underwater acoustics.
Acoustic Foam
An open-celled foam used for acoustic treatment is an Acoustic foam. It attenuates airborne sound waves, reducing their amplitude, for noise reduction or noise control purposes. The energy is dissipated as heat. Acoustic foam panels can be made in several colors, sizes, and thicknesses.
Acoustic foam can be attached to walls, doors (as a soundproof door), ceilings, and other features of a room to control noise levels, echoes, and vibrations, which are called acoustic panels or sound-absorbing panels or soundproof panels.
Many of the acoustic foam panels or products are treated with dyes and/or fire retardants.
Acoustic Treatment
Treating a room acoustically is important for audio production because of the fact that very few “spaces” contain physical qualities that make for desired recording or accurate monitoring. There are various things that are done to space before and during construction to optimize its acoustic behavior. These include the shape of the space, surface materials, and isolation. Once a room is constructed already, Acoustic Treatment mostly tends to consist of treating the surfaces. There are two primary elements to consider, which are diffusion and absorption.
Acoustic foam panels (sound free panels) are well suited to flutter echo and alleviate slap, the most two common problems in rooms not specifically designed for music sound recording and reproduction or performance. In fact, foam even can turn the gymnasium or most cavernous warehouse into a suitable acoustic environment. Diffusion holds wave sounds from grouping, so there are no nulls or hot spots in a room. In conjunction with absorption, diffusion effectively can turn any space virtually into a useful and appropriate for the recording or monitoring sound purpose with a high degree of accuracy.
Sound Pressure Level
Sound Pressure Level (SPL), usually refers to the root mean squared sound pressure of a sound relative to a reference value. The SPL is written as Lp.
A sound pressure level is the logarithmic measure of the root mean squared (RMS) sound pressure of a sound that is relative to a reference value.
A simple sound wave can be represented by a sine wave. A sine wave diagram which would be the typical output signal of a single tone noise level (a calibrator tone), if it is shown on an oscilloscope. The fundamental or basic parameters associated with a sound wave are Peak, Periodic Time, Peak-Peak, RMS (root-mean-square).
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Sound level meters measure the acoustic pressure, and by international agreement, they are calibrated in decibels (dB). The sound pressure level (Lp) in decibels is given as,
Lp = 20log (\[\frac{P}{P₀}\])
Where P is the sound pressure of measured root mean squared (RMS), and P0 is the RMS reference sound pressure (20µPa).
Also, note that the decibel is a ratio of two quantities having dimensions of power and is not a unit.
FAQs on Sound
1. What is sound and how is it produced?
Sound is a form of energy that travels as a wave and can be heard when it reaches an ear. It is always produced by vibrating objects. When an object vibrates, it causes the particles of the medium around it (like air, water, or a solid) to also vibrate. These vibrations pass from one particle to the next, creating a sound wave that propagates outwards from the source. For example, when you speak, your vocal cords vibrate, producing sound.
2. Why can't sound travel through a vacuum, such as in outer space?
Sound is a mechanical wave, which means it requires a medium (a substance made of particles like gas, liquid, or solid) to travel. Sound propagates by causing vibrations in these particles, which then bump into their neighbours, passing the vibration along. In a vacuum, there are essentially no particles to vibrate. Therefore, there is nothing to carry the sound vibrations from a source to a receiver, and sound cannot travel.
3. What are the main characteristics of a sound wave?
The main characteristics that define a sound wave and determine how we perceive it are:
- Amplitude: This relates to the intensity of the vibration and determines the loudness or volume of the sound. A wave with a larger amplitude carries more energy and sounds louder.
- Frequency: This is the number of vibrations per second and determines the pitch of the sound. A higher frequency creates a higher-pitched sound. It is measured in Hertz (Hz).
- Speed: This is how fast the sound wave travels through a medium. The speed of sound depends entirely on the properties of the medium, such as its density, temperature, and elasticity.
4. How do amplitude and frequency of a sound wave affect the sound we hear?
Amplitude and frequency are two independent properties of a sound wave that our brain interprets differently. Amplitude is perceived as loudness. A sound wave with a high amplitude displaces medium particles more, which our ears interpret as a loud sound. Conversely, frequency is perceived as pitch. A high-frequency wave makes our eardrum vibrate faster, which our brain interprets as a high-pitched or shrill sound. For example, a quiet whisper and a loud shout can have the same pitch if their frequencies are the same.
5. How are sound waves classified based on their frequency?
Based on the range of human hearing, sound waves are classified into three main categories:
- Audible Sound: This includes frequencies that the average human ear can detect, which is typically in the range of 20 Hz to 20,000 Hz (or 20 kHz).
- Infrasound: This refers to sound waves with frequencies below 20 Hz. Humans cannot hear them, but some animals like elephants and whales use them for communication. They are also produced by natural phenomena like earthquakes.
- Ultrasound: This refers to sound waves with frequencies above 20,000 Hz (20 kHz). It is inaudible to humans but is used by animals like bats and dolphins for echolocation and has many important medical and industrial applications.
6. What is the difference between an echo and reverberation?
Both are caused by the reflection of sound, but they are perceived differently due to timing. An echo is a single, distinct repetition of a sound that is heard after the original sound has ceased. It occurs when the time gap between the original sound and its reflection is long enough (at least 0.1 seconds) for the brain to distinguish them as separate sounds. Reverberation is the persistence of sound due to multiple, rapid reflections in a space. The reflections arrive at the ear so closely together that they merge, creating a prolonged, blended sound instead of a distinct echo.
7. What are some important real-world applications of ultrasound?
Ultrasound's high-frequency nature allows it to be used in various precise applications. Key examples include:
- Medical Diagnostics: In ultrasonography (e.g., pregnancy scans), it creates real-time images of internal body organs without harmful radiation.
- SONAR Systems: Used in ships and submarines for SOund Navigation And Ranging to map the seabed and detect underwater objects.
- Industrial Cleaning: High-intensity ultrasound waves can dislodge dirt and contaminants from delicate or complex machinery parts.
- Echolocation: Animals like bats and dolphins emit ultrasonic waves and interpret the returning echoes to navigate and hunt in complete darkness.
8. How does the human ear convert sound waves into signals the brain can understand?
The human ear is a sophisticated transducer that converts sound energy into electrical signals in three stages:
- Outer Ear: The pinna collects sound waves and funnels them through the ear canal to the eardrum, causing it to vibrate.
- Middle Ear: The eardrum's vibrations are transferred to three tiny, connected bones (hammer, anvil, and stirrup). These bones act as a lever system, amplifying the vibrations significantly.
- Inner Ear: The amplified vibrations are passed to the fluid-filled cochlea. Inside the cochlea, tiny hair cells detect the fluid's movement and convert these mechanical vibrations into electrical impulses, which are then sent to the brain via the auditory nerve to be interpreted as sound.
