The acoustics is a branch of physics which studies the production, transmission, storage, perception and reproduction of sound; that is to say, it studies in detail the sound waves that propagate through a matter, which can be in a gaseous, liquid or solid state, because sound does not propagate in a vacuum. Sound is the primary element in acoustics, and consists of sound waves that are produced when oscillations in air pressure are converted into mechanical waves.
What is Acoustics
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It is the branch of physics that studies the production and behavior during the transmission and destination of sound waves, as well as their composition. When talking about what acoustics is, it also refers to the study of physical spaces or venues where sound is propagated, and it has multiple applications for events, studios and public spaces.
Also in music, it is the term that is understood by the use of instruments that produce sounds acoustically, leaving aside electrical or electronic elements, for example, the acoustic guitar.
What does Acoustics study
They have amplitude (maximum and minimum values in its undulation), frequency (number of oscillations per second or repetitions), speed (the time that elapses from when it is generated until it reaches its receiver), length (how long the wave is or what distance exists between two peaks or valleys in it), period (time of each cycle for its repetition), amplitude (amount of signal energy, it does not mean volume), phase (position of one wave with respect to another) and power (amount of acoustic energy per time per source).
There are two types of waves according to the way they move through the media: longitudinal (the movement will be parallel to the direction of propagation) and transverse (the movement is perpendicular to the direction of propagation).
Within the acoustic phenomenon, not only the sound that can be easily perceived by the human ear is studied, but also infrasound and ultrasound. The infrasound are those sound frequencies that are lower than the human ear can perceive (20 hertz), but for some animals is quite noticeable and use as communication over large distances; while ultrasound is the waves that are above the hearing perceived by the human being, at about 20,000 hertz.
For this study, sound constitutes a transport of energy in the form of vibration, and its speed will depend on the density of the medium and the temperature of the air. The speed will be higher in solids and liquids than in gaseous media (air). The speed of sound in air is about 344 meters per second at about 20 ° C, although for each additional degree Celsius of temperature, the speed of the acoustic wave will increase at a rate of 0.6 m / s. In liquids, specifically water, the velocity will be around 1,440 m / s, while in solid ones like steel, it will be around 5,000 m / s.
History of Acoustics
Marco Vitruvio Polión (80 / 70-15 AC), Roman architect and engineer, was the forerunner of architectural acoustics, writing about the acoustic phenomena that took place in theaters, and thanks to this, there was a record of aspects that take into account the acoustic field when building theatrical and musical venues.
Later, the engineer, physicist and mathematician Galileo Galilei (1564-1642), concluded Pythagoras' studies, by defining waves more clearly, giving rise to physiological acoustics, and by describing it as a stimulus interpreted by the mind as sound, to psychological acoustics. Marin Mersenne (1588-1648), French philosopher and mathematician, carried out experiments on the speed of propagation of sound; and Isaac Newton (1643-1727), formulated the speed of sound in solids. Physicist John William Strutt (1842-1919), also known as Lord Rayleigh, wrote about the production of sound on strings, cymbals, and membranes.
Other famous people in history who contributed to the acoustic field were the astronomer, mathematician and physicist Pierre-Simon Laplace (1749-1827), with studies on the propagation of sound; Hermann von Helmholtz (1821-1894), physicist and physician, studied the relationship between tones and frequencies; Alexander Graham Bell (1847-1922), inventor and scientist, developed the telephone by observing that some materials could transform and transport sound vibrations; Thomas Alva Edison (1847-1931), inventor, achieved the amplification of sound vibrations with the development of the phonograph.
Branches of Acoustics
There are several classifications that, together, help define what acoustics is, according to the means of propagation of the waves and their practical utility. Some of them are:
Acoustics Acoustics
This is a redundant term, although many people are curious about it. Acoustics is present in all branches. For example, in physical acoustics, which is about the analysis of sound phenomena, the laws under which it is governed, its transport through the media and its properties; while acoustic metrology is the one in charge of calibrating instruments to measure acoustic magnitudes to record quantifications of the same or produce them.
Physiological Acoustics
Study the ears and throat, as well as the area of the brain that decodes the waves. Here both the sounds emitted and the perception of them and disorders are included.
Architectural Acoustics
It is responsible for the study of acoustics in enclosures and spaces, their behavior, how to adapt and set such spaces for the optimal use of the characteristics of sound and have an effective propagation in a controlled space. This division helped develop suitable enclosures for this purpose, such as the acoustic shell.
Industrial Acoustics
It is the branch that is responsible for attenuating the effects of noise produced by industrial activity, in order to protect workers from noise pollution and its attacks, by means of some type of acoustic insulation.
Environmental Acoustics
Study the sounds present in the outdoors, the noise in the environment and its effects on nature and people. These noises are generated by traffic, different types of transport, business premises, neighborhoods and different daily human activities. This branch promotes the management and control of noise, to reduce noise pollution.
Acoustic Pollution
Musical Acoustics
It is the one that studies the sound produced by musical instruments, their scales, chords, consonance. That is, the tuning of the scale of the same. In addition to those mentioned above, there are other branches, such as:
- Aeroacoustics (sound produced by movement in the air)
- Psychoacoustics (human perception of sound and its effects)
- Bioacoustics (studies hearing in animals and understanding their perception)
- Underwater (detection of objects with sound, such as radars)
- Slectroacoustics (studies electronic processes for the capture and processing of sound)
- Phonetics (acoustics of human speech)
- Macroacoustics (study of loud sounds)
- Ultrasonic (studies inaudible high frequency sound and its applications)
- Vibratory (study of systems that have mass and elasticity that can perform oscillatory movements)
- Structural (studies the sound that propagates through structures in the form of vibrations), among others.
Acoustic Phenomena
They are those distortions in sound waves, caused by obstacles or variations existing in the propagation medium that affect their characteristics. Among these acoustic phenomena are:
- Reflection: this is when the sound wave meets a solid obstacle and this causes it to deviate from its original course, creating a "bounce" effect, which allows it to return to the medium from which it comes.
- Echo - Occurs when a wave bounces off and is reflected in repeating cycles at an interval of approximately 0.1 seconds. To perceive it, the sound source and the surface that reflects it, must be separated by no less than 17 meters.
- Reverberation: This is a phenomenon similar to echo, with the difference that the repetition time is less than 0.1 seconds, and the resulting effect is a prolonged sound. In this case, the source and the reflecting surface must be less than 17 meters apart.
- Absorption: is when the wave reaches a surface and it neutralizes or absorbs part of it and the rest is reflected. Acoustic panels used in studios have this property, although they absorb sound almost entirely.
- Refraction: they are the curvatures that a sound takes when it passes from one medium to another, and its direction and speed will depend on the temperature, density and elasticity of the propagation medium.
- Diffraction: is when a wave encounters an obstacle smaller than its length in its path, which causes it to surround it and the wave to "disperse".
- Interference: occurs when two or more different waves intersect or overlap. Generally, they have opposite trajectories, so they will "collide" with each other. The more equal both waves have in terms of their amplitude, the greater the interference index.
- Pulsations: arise in the presence of two waves of different frequencies but very close, which is imperceptible to the human ear, so it is perceived as a single frequency.
- Doppler effect: it is the one that is perceived when an increase or decrease in the frequency of a wave arises when the emitter and the receiver move closer or farther away. Example: when you hear an ambulance or patrol coming, it passes by and drives away again.
What is noise pollution
It is the acoustic version of the alteration of an environment in a certain space. When there is noise pollution, then it will be understood that there is an excess of sound or noise that will alter the environment.
What is acoustic foam
There are two classes of elements designed to absorb at a certain scale: sound-absorbing materials and selective elements or also called resonators.
The former are used to obtain adequate reverberation times in the activities carried out in space, the reduction or elimination of echoes and for the elimination of polluting noise outside the site. The most widely used are coated stone wool, coated polyester fiber and flexible melamine resin foam.
The seconds are the ones used when looking to obtain a great absorption of low frequencies, reducing reverberation times in principle. They can be used as supplements to absorbent materials or separately for the purpose described above.
The types of resonators are:
- Membrane or diaphragmatic: non-porous and flexible materials, such as wood.
- Simple cavity: formed by a closed air cavity, which is connected to the room by a narrow opening.
- Cavity manifold based on slotted panels: panel of non-porous and rigid material that has been drilled a series of circles or slots, which will be located at a certain distance from the wall of the room, so that there is a space of closed air formed by both surfaces.
