Acoustics

thumb|A drum produces sound via a vibrating membrane.

thumb|alt=Lindsay's Wheel of acoustics|upright=1.75|Lindsay's Wheel of Acoustics, which shows fields within acoustics

frequency change of a wave for observer relative to its source

distance travelled during a unit of time by a sound wave propagating through an elastic medium

change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated

thumb|right|An ultrasonic examination

In audio signal processing and acoustics, an echo is a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is directly proportional to the distance of the reflecting surface from the source and the listener. Typical examples are the echo produced by the bottom of a well, a building, or the walls of enclosed and empty rooms.

excessive, displeasing human, animal, or machine-created environmental noise

The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 101/20 (approximately ).

device used to produce a fixed tone

diagnostic and therapeutic technique

thumb|right|Spectrogram of the first second of an E9 [[suspended chord played on a Fender Stratocaster guitar. Below is the E9 suspended chord audio: File:9577 Guitarz1970 Clean E9 Guitar Chord (Mike Tribulas).ogg ]]

mathematical curve that describes a smooth repetitive oscillation; continuous wave

physical system that responds to a restoring force inversely proportional to displacement

moving wave that consists of oscillations occurring perpendicular (right angled) to the direction of energy transfer (or the propagation of the wave)

thumb|384x384px|Reverb on a guitar

random signal having equal intensity at different frequencies, giving it a constant power spectral density

study of superpositions in mathematics

instantaneous product of sound pressure and particle velocity

branch of mathematics regarding periodic and continuous signals

sound associated with shock waves created when an object travels through the air faster than the speed of sound

alt=Image showing an audiologist testing the hearing of a patient inside a hearing booth and using an audiometer|thumb|upright=1.3|Audiological exam

measure comparing the level of a searched signal to the level of background noise

science and engineering of achieving a good sound within a building

right|thumb|Single-bubble sonoluminescence – a single, cavitating bubble Sonoluminescence is luminescence induced by sound waves, such as in the emission of light from imploding bubbles in a liquid when excited by sound. Sonoluminescence is sometimes considered a kind of mechanoluminescence. However, mechanoluminescence is typically defined as pertaining to solids, while sonoluminescence usually pertains to liquids. The related terms acoustoluminescence and sonotriboluminescence have been used to describe sound-induced luminescence in solids (e.g., crystals suspended in slurries).

the general use of reflected sound waves to locate objects

local pressure deviation from the ambient atmospheric pressure, caused by a sound wave

thumb|250px|The node (physics)|nodes of a vibrating string are harmonics. thumb|Two different notations of natural harmonics on the cello. First as sounded (more common), then as fingered (easier to sightread).

thumb|upright=1.2|Vibrational modes of an ideal string, dividing the string length into integer divisions, producing harmonic partials f, 2f, 3f, 4f, etc. (where f means fundamental frequency).

filter that passes signals with a frequency lower than a certain cutoff frequency, and attenuates signals with higher frequencies

Instrument that measures the magnitude of an input signal versus frequency within the full frequency range of the instrument

term in acoustics

upright=1.35|thumb|A pair of headphones being tested inside an [[anechoic chamber for soundproofing]]

thumb|400px|right|The horizontal axis shows frequency in [[Hertz]]

music genre, non-electric music created through acoustics

Psychoacoustics is the branch of psychophysics involving the scientific study of the perception of sound by the human auditory system. It is the branch of science studying the psychological responses associated with sound, including noise, speech, and music. Psychoacoustics is an interdisciplinary field including psychology, acoustics, electronic engineering, physics, biology, physiology, and computer science.

thumb|250px|right|An early phonautograph (1859). The barrel, for receiving sound, is made of plaster of Paris.

A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonator can be either electromagnetic or mechanical (including acoustic). Resonators are used to either generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones. Another example is quartz crystals used in electronic devices such as radio transmi

lowest frequency of a periodic waveform, such as sound

ability to pay attention to one conversation among many

250px|thumb|Spectrogram of American English vowels showing the formants F1 and F2|class=skin-invert-image

type of signal whose amplitude is inversely proportional to its frequency

exterior structure designed to protect inhabitants of sensitive land use areas from noise pollution

In physics, attenuation is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.

quotient of average sound pressure at a surface and sound volume flow rate through that surface

thumb|Spectrograms of [[Thrush nightingale (Luscinia luscinia) and Common nightingale (Luscinia megarhynchos) singing help to reliably distinguish these two species by voice.]] Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually, it refers to the investigation of sound production, dispersion and reception in animals (including humans). This involves neurophysiological and anatomical basis of sound production and detection, and relation of acoustic signals to the medium they disperse through. The findings provide clues about the evolution of acoustic mechan

technical room for sound recording or research

xeno-canto is a citizen science project and repository in which volunteers record, upload and annotate recordings of birds, orthoptera, bats, frogs and land mammals. Since it began in 2005, it has collected over 1,000,000 sound recordings from more than 12,900 species worldwide, and has become one of the biggest open collections of wildlife sounds in the world. All the recordings are published under one of the Creative Commons licenses, including some with open licences. Each recording on the website is accompanied by a spectrogram and location data on a map displaying geographical variation.

phenomenon of air resonance in a cavity

device for acoustic measurements

longitudinal wave that propagates by means of adiabatic compression and decompression;travels with the speed of sound which depends on the medium they're passing through

vocal practices found in different cultures of the world and that may involve a wide range of techniques for producing voice and song

experimental acoustical apparatus

thumb|upright=1.3|right|Equal-loudness contours The phon is a logarithmic unit of loudness level for tones and complex sounds. Loudness is measured in sones, a linear unit. Human sensitivity to sound is variable across different frequencies, so although two different tones may present an identical sound pressure to a human ear, they may be psychoacoustically perceived as differing in loudness. The purpose of the phon is to provide a logarithmic measurement (like decibels) for perceived sound magnitude, while the primary loudness standard methods result in a linear representation. A sound with

secondary ceiling hung below a main ceiling

In chemistry, the study of sonochemistry is concerned with understanding the effect of ultrasound in forming acoustic cavitation in liquids, resulting in the initiation or enhancement of the chemical activity in the solution. Therefore, the chemical effects of ultrasound do not come from a direct interaction of the ultrasonic sound wave with the molecules in the solution.

minimum sound level that an average individual can hear

biological process to identify the location or origin of a detected sound in direction and distance

periodic vibration whose frequency is audible to the average human

phenomenon where acoustic systems amplify sound waves whose frequency matches one of its own natural frequencies of vibration (its resonance frequencies)