Acoustics

Artificial omni-directional sound source in an anechoic chamber

Acoustics is the branch of physics that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Hearing is one of the most crucial means of survival in the animal world, and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as a key element of mating rituals or marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay's 'Wheel of Acoustics' is a well accepted overview of the various fields in acoustics.[1]

The word "acoustic" is derived from the Greek word ἀκουστικός (akoustikos), meaning "of or for hearing, ready to hear"[2] and that from ἀκουστός (akoustos), "heard, audible",[3] which in turn derives from the verb ἀκούω (akouo), "I hear".[4]

The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics[5] and later a branch of acoustics.[6] Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively.

History

Early research in acoustics

The fundamental and the first 6 overtones of a vibrating string. The earliest records of the study of this phenomenon are attributed to the philosopher Pythagoras in the 6th century BC.

In the 6th century BC, the ancient Greek philosopher Pythagoras wanted to know why some combinations of musical sounds seemed more beautiful than others, and he found answers in terms of numerical ratios representing the harmonic overtone series on a string. He is reputed to have observed that when the lengths of vibrating strings are expressible as ratios of integers (e.g. 2 to 3, 3 to 4), the tones produced will be harmonious, and the smaller the integers the more harmonious the sounds. If, for example, a string of a certain length would sound particularly harmonious with a string of twice the length (other factors being equal). In modern parlance, if a string sounds the note C when plucked, a string twice as long will sound a C an octave lower. In one system of musical tuning, the tones in between are then given by 16:9 for D, 8:5 for E, 3:2 for F, 4:3 for G, 6:5 for A, and 16:15 for B, in ascending order.[7]

Aristotle (384–322 BC) understood that sound consisted of compressions and rarefactions of air which "falls upon and strikes the air which is next to it...",[8] a very good expression of the nature of wave motion.

In about 20 BC, the Roman architect and engineer Vitruvius wrote a treatise on the acoustic properties of theaters including discussion of interference, echoes, and reverberation—the beginnings of architectural acoustics.[9] In Book V of his De architectura (The Ten Books of Architecture) Vitruvius describes sound as a wave comparable to a water wave extended to three dimensions, which, when interrupted by obstructions, would flow back and break up following waves. He described the ascending seats in ancient theaters as designed to prevent this deterioration of sound and also recommended 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 more desirable, harmonious notes.[10][11][12]

During the Islamic golden age, Abū Rayhān al-Bīrūnī (973-1048) is believed to postulated that the speed of sound was much slower than the speed of light.[13][14]

Principles of acoustics have been applied since ancient times : A Roman theatre in the city of Amman.

The physical understanding of acoustical processes advanced rapidly during and after the Scientific Revolution. Mainly Galileo Galilei (1564–1642) but also Marin Mersenne (1588–1648), independently, discovered the complete laws of vibrating strings (completing what Pythagoras and Pythagoreans had started 2000 years earlier). Galileo wrote "Waves are produced by the vibrations of a sonorous body, which spread through the air, bringing to the tympanum of the ear a stimulus which the mind interprets as sound", a remarkable statement that points to the beginnings of physiological and psychological acoustics. Experimental measurements of the speed of sound in air were carried out successfully between 1630 and 1680 by a number of investigators, prominently Mersenne. Meanwhile, Newton (1642–1727) derived the relationship for wave velocity in solids, a cornerstone of physical acoustics (Principia, 1687).

Age of Enlightenment and onward

The eighteenth century saw major advances in acoustics as mathematicians applied the new techniques of calculus to elaborate theories of sound wave propagation. In the nineteenth century the major figures of mathematical acoustics were Helmholtz in Germany, who consolidated the field of physiological acoustics, and Lord Rayleigh in England, who combined the previous knowledge with his own copious contributions to the field in his monumental work The Theory of Sound (1877). Also in the 19th century, Wheatstone, Ohm, and Henry developed the analogy between electricity and acoustics.

The twentieth century saw a burgeoning of technological applications of the large body of scientific knowledge that was by then in place. The first such application was Sabine’s groundbreaking work in architectural acoustics, and many others followed. Underwater acoustics was used for detecting submarines in the first World War. Sound recording and the telephone played important roles in a global transformation of society. Sound measurement and analysis reached new levels of accuracy and sophistication through the use of electronics and computing. The ultrasonic frequency range enabled wholly new kinds of application in medicine and industry. New kinds of transducers (generators and receivers of acoustic energy) were invented and put to use.

Other Languages
العربية: علم الصوت
asturianu: Acústica
azərbaycanca: Akustika
беларуская: Акустыка
български: Акустика
Boarisch: Akustik
bosanski: Akustika
català: Acústica
čeština: Akustika
Cymraeg: Acwsteg
dansk: Akustik
Deutsch: Akustik
eesti: Akustika
Ελληνικά: Ακουστική
español: Acústica
Esperanto: Akustiko
euskara: Akustika
français: Acoustique
Gaeilge: Fuaimíocht
galego: Acústica
한국어: 음향학
हिन्दी: ध्वनिकी
hrvatski: Akustika
italiano: Acustica
עברית: אקוסטיקה
қазақша: Акустика
Kreyòl ayisyen: Akoustik
Кыргызча: Акустика
Latina: Acustica
latviešu: Akustika
Lëtzebuergesch: Akustik
lietuvių: Akustika
magyar: Akusztika
Bahasa Melayu: Akustik
Nederlands: Akoestiek
日本語: 音響学
norsk: Akustikk
norsk nynorsk: Akustikk
oʻzbekcha/ўзбекча: Akustika
Piemontèis: Acùstica
Plattdüütsch: Akustik
polski: Akustyka
português: Acústica
română: Acustică
русский: Акустика
Scots: Acoustics
shqip: Akustika
sicilianu: Acùstica
Simple English: Acoustics
slovenčina: Akustika
slovenščina: Akustika
српски / srpski: Акустика
srpskohrvatski / српскохрватски: Akustika
suomi: Akustiikka
svenska: Akustik
Tagalog: Akustika
தமிழ்: ஒலியியல்
тоҷикӣ: Акустика
Türkçe: Akustik
тыва дыл: Акустика
українська: Акустика
اردو: صدائیات
Tiếng Việt: Âm học
Winaray: Akustika
Zazaki: Akustik
中文: 声学