The acoustics ( gr ἀκούειν akoyein, hear ') is the study of sound and its propagation. As a scientific field it covers all related aspects, the creation and generation, propagation, the influence and the analysis of sound, its perception by the ear and effect on humans and animals. Acoustics is an interdisciplinary field that builds on findings from numerous other disciplines, including physics, psychology, communications engineering and materials science.
Among the most important applications of acoustics in addition to the exploration and reduction of noise also includes the effort to bring about a harmony or to transfer acoustic information. Moreover, the use of sound for the diagnosis or for technical purposes is an important application of acoustics.
- 4.1 Anechoic chamber
- 4.2 anechoic chamber
- 4.3 echo chamber
- 5.1 Acoustics in animals
- 5.2 Phonology
History of acoustics
As a first systematic study of the acoustics have identified the introduction of sound systems and moods in music in the 3rd millennium BC in China. From ancient times, the scientific study of acoustics, among others, of Pythagoras of Samos (ca. 570-510 BC) narrated the mathematically analyzed the relationship between string length and pitch of the monochord. Chrysippus of Soli ( 281-208 BC) recognized the wave nature of sound through a comparison with waves on the water surface. The Roman architect Vitruvius ( ca 80-10 BC ) analyzed the propagation of sound in amphitheatres and assumed the propagation of sound as a spherical wave. He also described the mode of action of Helmholtz resonators to absorb low frequency sound.
Leonardo da Vinci (1452-1519) realized that air is required, among other things as a medium for the propagation of sound and that sound propagates at a finite speed. From Marin Mersenne (1588-1648) comes in addition to other scientific knowledge for the nature of sound, the first indication of an experimentally determined speed of sound. Galileo Galilei (1564-1642) described the importance for the acoustic relationship between pitch and frequency. Joseph Sauveur (1653-1716) introduced the term " acoustic " for the study of sound. Isaac Newton (1643-1727), calculated as a first the speed of sound on the basis of theoretical considerations, while Leonhard Euler (1707-1783) found a wave equation for sound in the form used today. Ernst Florens Friedrich Chladni (1756-1827) is considered the founder of modern experimental acoustics; he invented the Chladni figures, make the natural vibrations of plates visible.
With the beginning of the 19th century put an intense preoccupation with an acoustic and a number of scientists devoted themselves to the subject. So was Pierre- Simon Laplace (1749-1827), the adiabatic behavior of sound, Georg Simon Ohm (1789-1854) postulated the ability of the auditory system to resolve sounds in fundamental tones and harmonics, Hermann von Helmholtz (1821-1894) explored the sensation of sound and described the Helmholtz resonator and John William Strutt, 3rd Baron Rayleigh ( 1842-1919 ) published the " Theory of Sound " with numerous mathematically substantiated findings that affect the sound, its emergence and spread.
In the second half of the 19th century first acoustic measuring and recording devices are developed, the Phonautograph by Édouard -Léon Scott de Martinville ( 1817-1897 ) and later the phonograph by Thomas Alva Edison ( 1847-1931 ). August Kundt (1839-1894) developed the Kundt's tube and put it for the measurement of sound absorption coefficient.
From the beginning of the 20th century it came to the wide application of existing theoretical knowledge on acoustics. Thus, the Wallace Clement Sabine, founded by scientific acoustics developed with the aim to improve the acoustic quality of rooms. The invention of the electron tube 1907 allowed the widespread use of electro-acoustic transmission technology. Paul Langevin (1872-1946) used ultrasound to technical locate objects under water (sonar ). Heinrich Barkhausen (1881-1956) invented the first device to measure the volume. Since about 1930 scientific journals, devote themselves exclusively subjects of acoustics appear.
At one of the most important applications of acoustics in the first half of the 20th century is also developing the reduction of noise, such as the silencer for the exhaust system of motor vehicles is continuously improved. With the introduction of jet engines in the 1950s and the conditions necessary for successful use of noise reduction, the aeroacoustics, which was significantly influenced by the work of James Lighthill ( 1924-1998 ) founded developed.
Working areas of acoustics
Within the acoustics a variety of different work areas are covered:
- In Physical acoustics, the physics of acoustics are treated.
- Aeroacoustics is concerned with the emergence and spread of aerodynamically generated noise and its reduction.
- The hydroacoustic deals with underwater sound
- The electro-acoustics deals with the recording, processing and reproduction of sound.
- The Technical Acoustics treated sounds of machinery and equipment.
- The thermal acoustics deals with the coupling of heat release and acoustic pressure.
- The noise research is concerned with all aspects of noise generation, reduction and perception.
- In room acoustics and building acoustics the issues of sound transmission in buildings and the sound of auditoriums are treated.
- In the vehicle acoustics all issues relating to indoor and outdoor noise of vehicles to be treated.
- The Musical Acoustics deals with the production and perception of music.
- Psychoacoustics deals with issues for sound perception and the subjective assessment of sound and the objectification of subjective perception in which musicology with the help of music psychology
- The phonetics deals with the speech processing and communication.
- In medicine, the audiometry is used for measurement of parameters of the hearing.
In addition to considering time- averaged sound field and sound energy quantities, the time deflection is often measured, eg the pressure signal, and a frequency analysis subject. In the context of the resulting frequency spectrum with the sound see sound spectrum. The change over time in an acoustic event is accessible by short-time Fourier transform. The changes in the spectrum in the process of sound radiation, propagation and measurement or perception can be described by the corresponding frequency response. The frequency response of the hearing into account frequency weighting curves.
The acoustic resonance analysis evaluates the resulting resonant frequencies when a body is rotated by a pulse -like excitation such as a blow to vibrate. Is the body an oscillatory system, so forming over a period of time certain characteristic frequencies, the body oscillates in the so-called natural natural or resonance frequencies - short resonances.
In order analysis noise or vibrations are analyzed by the rotating machine, wherein in contrast to the frequency analysis in this case, the energy content of the noise is not applied to the frequency, but to the right. The order corresponds to a multiple of the speed.
An anechoic chamber, sometimes physically incorrect also called " anechoic " room has absorbent material to ceiling and walls, so that only minimal reflections occur and prevail conditions as in a direct field D (free-field or free sound field ), the sound pressure with 1 / r according to the law of distance from a point source decreases. Such spaces are suitable for voice recordings and for the localization of sound sources. If measured on an imaginary envelope to the sound source, the perpendicular passing through this surface sound intensity, the sound power of the source can be determined.
An anechoic chamber is a special version of an anechoic chamber. Here, however, the floor is also covered with absorbent material. Because the soil is no longer accessible by this measure, a sound- permeable mesh is usually placed about giving access to the measurement object. Such premises are used in the acoustic measurement technique to get targeted sound source analysis - even under the measurement object - to perform can.
A reverberation chamber, however, is designed to meet at any point in the sound field reflections of the same size from all directions. In an ideal reverberation chamber therefore there with the exception of the area right around the sound source ( see Hall radius ) at each place the same sound pressure. Such a sound field is called diffuse field. Since the sound rays are incident from all directions at the same time, no sound intensity is present in a diffuse field. To avoid resonances in an echo chamber, he is generally constructed without mutually parallel walls and ceilings. About reverberation time measurements or by reference sound sources, the space can be calibrated. Here, the difference between the measured at any location in space, far enough outside the reverberation radius sound pressure level and sound power level of a sound source is determined. This difference depends on the frequency and remains unchanged as long as the structure does not change the space and the degree of absorption of the walls. In a reverberation chamber can therefore theoretically be determined with a single measurement, the sound pressure sound power of a source. This is for example very useful for problems in the field of sound insulation.
Acoustic in nature
Acoustics in animals
Most higher animals have a sense of hearing. Noise is a major communication channel, since it has practically immediate action at a distance. With vocalizations animals is a means of territorial marking, partner or pack search, to find prey and in communication of moods, warning signals, etc., is added. The human hearing range is between the hearing threshold and the pain threshold ( about 0 dB HL to 110 dB HL).
In the generation of sounds in the context of phonology, a distinction is generally between voiced and unvoiced phonemes. In the voiced phonemes, which are referred to as vowels, are the larynx by vibration of the vocal cords, the " raw " sounds generated, which are then modulated by various arbitrarily modifiable or unalterable individual specific resonance chambers of the throat and nasal passages. For unvoiced phonemes, consonants, rest the vocal cords, the sound by modulating the flow of air is established. When you whisper the vowels themselves are formed only by modulation of the spectrum of the noise out of a compressed air stream, and rest the vocal cords.
Experts for acoustics are called acoustic / or in acoustics engineer / in. English job titles are acoustical engineer or acoustician. The usual access to this field of work is a study in physics or an equivalent engineering degree.