Acoustics is defined by ANSI/ASA S1.1-2013") as "(a) Science of sound, including its production, transmission, and effects, including biological and psychological effects. (b) Those qualities of a room that, together, determine its character with respect to auditory effects."

The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations.

The steps shown in the diagram above can be found in any acoustic event or process. There are many types of causes, both natural and volitional. There are many types of transduction processes that convert energy from some other form into sonic energy, producing a sound wave. There is a fundamental equation that describes the propagation of the sound wave, the "acoustic wave equation", but the phenomena that arise from it are varied and often complex. The wave carries energy through the medium of propagation. Finally, this energy is transduced back to other forms, in ways that can also be natural and/or voluntarily artificial. The final effect can be purely physical or enter into biological or volitional realms. The five basic stages apply equally whether we are talking about an earthquake or a submarine using a sonar to locate your enemy or a band playing at a rock concert.

The central stage of the acoustic process is the propagation of waves. This falls within the domain of physical acoustics. In fluids, sound travels primarily as a pressure wave. In solids, mechanical waves can take various forms, such as longitudinal waves, transverse waves, and surface waves.

Acoustics first studies the pressure levels and frequencies of the sound wave and how it interacts with the environment. This interaction can be described as diffraction, interference or a reflection "Reflection (physics)") or a mixture of the three. If there are multiple media, a Refraction can also occur. Transduction processes are also of particular importance for acoustics.

Wave Propagation: Pressure Levels

In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. Although this disturbance is usually small, it is still perceptible to the human ear. The smallest sound a person can hear, known as the hearing threshold, is nine orders of magnitude lower than ambient pressure. The "Loudness (psychoacoustic)") intensity of these disturbances is related to the sound pressure level (SPL), which is measured on a logarithmic scale in decibels.

Wave propagation: frequency

Physicists and acoustic engineers tend to talk about sound pressure levels in terms of frequencies, partly because that's how our ears interpret sound. What we experience as "higher" or "lower" sounds are pressure vibrations with a greater or lesser number of cycles per second. In a common acoustic measurement technique, acoustic signals are sampled in time and then presented in more meaningful forms, such as octave bands or time-frequency graphs. Both popular methods are used to analyze sound and better understand the acoustic phenomenon.

The full spectrum can be divided into three sections: audio, ultrasonic and infrasonic. The audio range is between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear. This range has numerous applications, such as spoken communication and music. The ultrasonic range refers to very high frequencies: 20,000 Hz and higher. This range has shorter wavelengths that allow for better resolution in imaging technologies. Medical applications, such as medical ultrasonography and elastography, rely on the range of ultrasonic frequencies. At the other end of the spectrum, the lower frequencies are known as the infrasonic range. These frequencies can be used to study geological phenomena such as earthquakes.

Analytical instruments such as the spectrum analyzer facilitate the visualization and measurement of acoustic signals and their properties. The spectrogram produced by such an instrument is a graphical representation of the temporal variation of the pressure level and frequency profiles that give a specific acoustic signal its defining character.

Transduction in acoustics

A transducer is a device for converting one form of energy into another. In an electroacoustic context, this means converting sound energy into electrical energy (or vice versa). Electroacoustic transducers include loudspeakers, microphones, particle velocity sensors, hydrophones, and projector sonars. These devices convert a sound wave into or from an electrical signal. The most used transduction principles are electromagnetism, electrostatics and piezoelectricity.

The most common speaker transducers (for example, woofers and tweeters) are electromagnetic devices that generate waves through a suspended diaphragm driven by an electromagnetic voice coil, emitting pressure waves. Electret microphones and condenser microphones are electrostatic: when the sound wave hits the microphone diaphragm, it moves and induces a change in voltage. Ultrasonic systems used in medical ultrasonography employ piezoelectric transducers. They are made with special ceramics in which mechanical vibrations and electrical fields are interrelated due to a property of the material itself.

Some branches of acoustic physics are:

First jobs

Acoustics has its origin in Ancient Greece and Rome, between the 6th centuries BC. C. and I d. C. It began with music, which had been practiced as an art for thousands of years, but had not been studied scientifically until Pythagoras became interested in the nature of musical intervals. He wanted to know why some intervals sounded more beautiful than others, and he came up with answers in the form of numerical ratios.

Aristotle (384 BC) found that sound consisted of contractions and expansions of air "falling on and striking the nearby air", a good way of expressing the nature of the movement of waves. Around the year , the Roman architect and engineer Vitruvius wrote a treatise on the acoustic properties of theaters, including topics such as interference, echoes, and reverberation; This marked the beginning of architectural acoustics.[6]​.

He described the rising seats of ancient theaters as being designed to prevent this deterioration of sound and also recommended that bronze vessels of appropriate sizes be placed in theaters to resonate with the fourth, fifth, and so on, up to the double octave, in order to resonate with the most desirable and harmonious notes.[7]​[8][9]​.

Understanding the physics of acoustic processes advanced rapidly during and after the Scientific Revolution. Galileo (1564-1642) and Marin Mersenne (1588-1648) independently discovered all the laws of the vibrating string, thus finishing the work that Pythagoras had begun 2000 years earlier. Galileo wrote "Waves are produced by the vibrations of a sound body, which diffuse through the air, carrying to the eardrum of the ear a stimulus that the mind interprets as sound", thus laying the beginning of physiological and psychological acoustics.

Between 1630 and 1680, experimental measurements of the speed of sound in air were made by a series of researchers, notably Mersenne. Meanwhile, Newton (1642-1727) obtained the formula for wave speed in solids, one of the pillars of acoustic physics (Principia, 1687).

From the Enlightenment onwards

The century saw great advances in acoustics at the hands of the great mathematicians of the era, who applied new calculation techniques to the development of the theory of wave propagation.

In the 19th century, the giants of acoustics were Helmholtz in Germany, who consolidated physiological acoustics, and Lord Rayleigh in England, who combined previous knowledge with abundant contributions of his own in his monumental work "The Theory of Sound." Also during that century, Wheatstone, Ohm, and Henry developed the analogy between electricity and acoustics.

During the century many technological applications of previous scientific knowledge appeared. The first was Wallace Clement Sabine's work on architectural acoustics, followed by many others. Underwater acoustics were used to detect submarines in World War I. Sound recording and the telephone were important for the transformation of global society. Sound measurement and analysis reached new levels of precision and sophistication through the use of electronics and computing. The use of ultrasonic frequencies allowed new types of applications in medicine and industry. New types of transducers (acoustic energy generators and receivers) were also invented.

Acoustics is defined by ANSI/ASA S1.1-2013") as "(a) Science of sound, including its production, transmission, and effects, including biological and psychological effects. (b) Those qualities of a room that, together, determine its character with respect to auditory effects."

The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations.

The steps shown in the diagram above can be found in any acoustic event or process. There are many types of causes, both natural and volitional. There are many types of transduction processes that convert energy from some other form into sonic energy, producing a sound wave. There is a fundamental equation that describes the propagation of the sound wave, the "acoustic wave equation", but the phenomena that arise from it are varied and often complex. The wave carries energy through the medium of propagation. Finally, this energy is transduced back to other forms, in ways that can also be natural and/or voluntarily artificial. The final effect can be purely physical or enter into biological or volitional realms. The five basic stages apply equally whether we are talking about an earthquake or a submarine using a sonar to locate your enemy or a band playing at a rock concert.

The central stage of the acoustic process is the propagation of waves. This falls within the domain of physical acoustics. In fluids, sound travels primarily as a pressure wave. In solids, mechanical waves can take various forms, such as longitudinal waves, transverse waves, and surface waves.

Acoustics first studies the pressure levels and frequencies of the sound wave and how it interacts with the environment. This interaction can be described as diffraction, interference or a reflection "Reflection (physics)") or a mixture of the three. If there are multiple media, a Refraction can also occur. Transduction processes are also of particular importance for acoustics.

Wave Propagation: Pressure Levels

In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. Although this disturbance is usually small, it is still perceptible to the human ear. The smallest sound a person can hear, known as the hearing threshold, is nine orders of magnitude lower than ambient pressure. The "Loudness (psychoacoustic)") intensity of these disturbances is related to the sound pressure level (SPL), which is measured on a logarithmic scale in decibels.

Wave propagation: frequency

Physicists and acoustic engineers tend to talk about sound pressure levels in terms of frequencies, partly because that's how our ears interpret sound. What we experience as "higher" or "lower" sounds are pressure vibrations with a greater or lesser number of cycles per second. In a common acoustic measurement technique, acoustic signals are sampled in time and then presented in more meaningful forms, such as octave bands or time-frequency graphs. Both popular methods are used to analyze sound and better understand the acoustic phenomenon.

The full spectrum can be divided into three sections: audio, ultrasonic and infrasonic. The audio range is between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear. This range has numerous applications, such as spoken communication and music. The ultrasonic range refers to very high frequencies: 20,000 Hz and higher. This range has shorter wavelengths that allow for better resolution in imaging technologies. Medical applications, such as medical ultrasonography and elastography, rely on the range of ultrasonic frequencies. At the other end of the spectrum, the lower frequencies are known as the infrasonic range. These frequencies can be used to study geological phenomena such as earthquakes.

Analytical instruments such as the spectrum analyzer facilitate the visualization and measurement of acoustic signals and their properties. The spectrogram produced by such an instrument is a graphical representation of the temporal variation of the pressure level and frequency profiles that give a specific acoustic signal its defining character.

Transduction in acoustics

A transducer is a device for converting one form of energy into another. In an electroacoustic context, this means converting sound energy into electrical energy (or vice versa). Electroacoustic transducers include loudspeakers, microphones, particle velocity sensors, hydrophones, and projector sonars. These devices convert a sound wave into or from an electrical signal. The most used transduction principles are electromagnetism, electrostatics and piezoelectricity.

The most common speaker transducers (for example, woofers and tweeters) are electromagnetic devices that generate waves through a suspended diaphragm driven by an electromagnetic voice coil, emitting pressure waves. Electret microphones and condenser microphones are electrostatic: when the sound wave hits the microphone diaphragm, it moves and induces a change in voltage. Ultrasonic systems used in medical ultrasonography employ piezoelectric transducers. They are made with special ceramics in which mechanical vibrations and electrical fields are interrelated due to a property of the material itself.

Some branches of acoustic physics are: