Acoustics: History & Applications

• Acoustics addresses mechanical waves in gases, liquids, and solids, including vibration, sound, ultrasound, and infrasound.
• Acoustics is concerned with the production, control, transmission, reception, and effects of sound
• An acoustician works in the field of acoustics, while an acoustical engineer works in acoustics technology
• The term "acoustics" comes from the Greek word "akoustos," meaning "heard."

Brief History of Acoustics

• Pythagoras (6th century BC) is credited with founding acoustics through experiments on vibrating strings and musical intervals
• Aristotle (4th century BC) correctly proposed that sound propagates through air via air motion, but incorrectly stated that high frequencies travel faster than low frequencies
• Vitruvius, a 1st century BC Roman engineer, determined the mechanism for sound wave transmission and substantially contributed to theatre acoustic design
• Boethius, a 6th century AD Roman philosopher, theorized that pitch perception relates to the physical property of frequency
• Galileo Galilei (1564-1642) originated the modern study of waves and acoustics, and he elevated the study of vibrations and the correlation between pitch and frequency.
• Marin Mersenne studied vibrating strings, summarizing his findings in three laws; his 1636 Harmonicorum Libri laid the basis for modern musical acoustics
• Robert Hooke produced a known frequency sound wave using a rotating cog wheel, establishing a method for measurement
• Félix Savart further developed this device in the 19th century, and Savart's disk is still used for physics lecture demonstrations

Age of Enlightenment and Onward

• Significant progress in acoustics occurred in the 18th century with contributions from Euler (1707-1783), Lagrange (1736-1813), and d'Alembert (1717-1783)
• During the 18th century, continuum physics or field theory began to receive definition mathematical structures through acoustics study
• The wave equation emerged, including in the context of the propagation of sound in air
• Major figures in 19th-century mathematical acoustics were Helmholtz, who consolidated physiological acoustics, and Lord Rayleigh who combined previous knowledge with his own contributions in The Theory of Sound (1877).

Technological Applications

• The 20th century saw a growth of technological applications of scientific knowledge
• Wallace Sabine's work in architectural acoustics (Boston Symphony Hall) was the first application.
• Underwater acoustics was used to detect submarines in World War I
• Sound recording and the telephone globally transformed society
• The ultrasonic frequency range enabled new applications in medicine and industry

Fields of Acoustics

• The "Wheel of Acoustics" was created by R. Bruce Lindsay and published in the Journal of the Acoustical Society of America
• The wheel shows the breadth of acoustics, starting with Earth Sciences, Engineering, Life Sciences, and the Arts
• The outer circle of the Wheel of Acoustics lists broad disciplines for career preparation
• The inner circle lists specific fields within acoustics

General Acoustics

• This includes the science of waves and how sound is created, travels, and is received
• It also covers how materials react to sound, with specific fields like Engineering Acoustics, Physical Acoustics, and Signal Processing

Engineering Acoustics

• Acoustical engineering is the branch of engineering dealing with sound and vibration
• Applies acoustics, the science of sound and vibration, in technology, focusing on sound design, analysis, and control
• The reduction of unwanted noise, or noise control, is a goal
• Acoustical engineering also covers positive uses of sound like ultrasound in medicine, digital synthesizers, design of concert halls to enhance sound, and railway station sound systems

Physical Acoustics

• Analyzes interactions of acoustic waves with gaseous, liquid, or solid mediums on macro- and micro-levels
• Studies sound interaction with thermal waves in crystals (phonons), with light (photons), with electrons in metals and semiconductors, and with magnetic excitations in ferromagnetic crystals

Acoustic Signal Processing

• This is the electronic manipulation of acoustic signals
• Manipulates acoustic signals for use in active noise control, design for hearing aids or cochlear implants, echo cancellation, music information retrieval, and perceptual coding

Animal Bioacoustics

• Animal bioacoustics is a field of research that encompasses sound production and reception by animals, animal communication, biosonar, active and passive acoustic technologies for population monitoring, acoustic ecology, and the effects of noise on animals.
• It is studied by experts from fields like engineering, physics, geophysics, oceanography, biology, mathematics, psychology, ecology, and computer science
• A key motivation for studying animal bioacoustics is conservation
• Passive listening provides a noninvasive and efficient tool to monitor population abundance, distribution, and behavior

Understanding Soundscapes

• Listening not only to animals, but also the sounds of the physical environment and man-made sounds, all of which make up a soundscape, allows monitoring of systems, their health, and changes over time
• Understanding bioacoustic systems advances the development of biomimetic technology like sonar hardware and software
• Studying animal hearing and hearing impairment holds great potential for understanding human hearing and mitigating human auditory injury and disease

Bioacoustic Monitoring

• Human activity causes the disappearance of various animal species at an alarming rate, leading to a new crisis related to eradiation of biodiversity
• Many critically endangered species are very rare, mysterious animals that live in hiding, which will probably die out before they are fully documented
• It offers significant promise, especially for species whose behavior or ecology reduces their detectability using traditional methods
• Individual recognition by means of the acoustic features of vocalizations can be achieved in several animal taxa, from frogs to mammals and birds, and is one of the best examples of the application of acoustic analysis to population
• Climate change affects biotic and abiotic interactions, environmental acoustics, and communication between animals
• This in turn, leads to changes in entire soundscapes, affects biodiversity, as some species are unable to adapt quickly the the changing environment
• Serves as a tool for measuring the impact of human activities on the environment not only only in water, but also on land

Medical Acoustics

• Doctors and researchers use acoustics to diagnose + treat ailments.
• The study of medical acoustics covers how different types of sound interact with cells, tissues, organs and entire organisms.
• Biomedical acousticians may work with engineers, physicians and speech therapists
• This can be subdivided into diagnostics and therapy.
• Diagnostics are separated into auditory and ultrasonic methods, using lower amplitudes than those needed for therapy
• Therapy uses ultrasound for heating, cooking, permeabilizing, activating and fracturing tissues within the body. This employs higher amplitudes than diagnostics

Musical Acoustics

• This field combines knowledge of physics, psychophysics, organology classification, physiology, music theory, ethnomusicology, signal processing and the study of instrument building
• Concerned with researching and describing the physics of music, it studies how sounds are employed to make music
• Study in this field includes the function of musical instruments, the human voice (the physics of speech and singing), computer analysis of melody, and in the clinical use of music in music therapy
• This the data and methods of general physical acoustics, which studies the processes of generation and propagation of sound
• Closely allied with architectural acoustics, the psychology of perception, and the physiology of hearing and the voice
• The eminent German physical scientist and physiologist H. L. F. von Helmholtz proposed the first complete conception of the physiology of pitch discrimination, called the resonance theory of hearing.

Noise and Environmental Acoustics

• Concerned with noise and vibration caused by railways, road traffic, aircraft, industrial equipment and recreational activities.
• Aims to reduce levels of environmental noise and vibration, through noise shielding etc
• Includes acoustic metrology, in order to quantify the noise emissions of a source with applicable regulation standards
• Includes modelling the preformance of acoustic solutions like insulated wals and rooms to reduce noise etc
• Construction technologies also apply in noise envrionmental acoustic projects.
• This includes industrial processes involving the area of energy of for test benches and testing rooms, and the physics of heat transfe
• Related to noise related to road and rail transporation infrastucture

Speech and Hearing

• Experts study how our ears sense sounds, what damages our ears, and how speech is made, travels, and is heard.
• This includes Speech Communication, Physiological and Psychological Acoustics, Noise,

Underwater Acoustics

• Underwater Acoustics studies sounds moving through water. such as the study of the surface of water, deep underwater, or along the ocean floor.
• Some applicatoins include underwater travel, seismic activity etc

Architectural Acoustics

• Architectural acoustics involves achieving a desired sound within a building by engineering a space, and is a branch of acoustical engineering
• Involves achieving speech intelligibility in a theatre, restaurant or railway station, enhancing the quality of music in a concert hall or recording studio, or suppressing noise to make offices and homes more productive
• Wallace Sabine pioneered it's scientific study in the Fogg Museum lecture room after designing Symphony Hall, Boston.