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104-399: 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

208-444: A l = γ ⋅ p ρ = γ ⋅ R ⋅ T M = γ ⋅ k ⋅ T m , {\displaystyle c_{\mathrm {ideal} }={\sqrt {\gamma \cdot {p \over \rho }}}={\sqrt {\gamma \cdot R\cdot T \over M}}={\sqrt {\gamma \cdot k\cdot T \over m}},} where This equation applies only when

312-596: A Bachelor's degree or higher qualification. Some possess a degree in acoustics, while others enter the discipline via studies in fields such as physics or engineering . Much work in acoustics requires a good grounding in Mathematics and science . Many acoustic scientists work in research and development. Some conduct basic research to advance our knowledge of the perception (e.g. hearing , psychoacoustics or neurophysiology ) of speech , music and noise . Other acoustic scientists advance understanding of how sound

416-402: A dispersive medium , the speed of sound is a function of sound frequency, through the dispersion relation . Each frequency component propagates at its own speed, called the phase velocity , while the energy of the disturbance propagates at the group velocity . The same phenomenon occurs with light waves; see optical dispersion for a description. The speed of sound is variable and depends on

520-711: A building from earthquakes, or measuring how structure-borne sound moves through buildings. Ultrasonics deals with sounds at frequencies too high to be heard by humans. Specialisms include medical ultrasonics (including medical ultrasonography), sonochemistry , ultrasonic testing , material characterisation and underwater acoustics ( sonar ). Underwater acoustics is the scientific study of natural and man-made sounds underwater. Applications include sonar to locate submarines , underwater communication by whales , climate change monitoring by measuring sea temperatures acoustically, sonic weapons , and marine bioacoustics. Hearing (sense) Hearing , or auditory perception ,

624-582: A clinical setting, this management is offered by otologists and audiologists . Hearing loss is associated with Alzheimer's disease and dementia with a greater degree of hearing loss tied to a higher risk. There is also an association between type 2 diabetes and hearing loss . Hearing threshold and the ability to localize sound sources are reduced underwater in humans, but not in aquatic animals, including whales, seals, and fish which have ears adapted to process water-borne sound. Not all sounds are normally audible to all animals. Each species has

728-453: A compression wave in a fluid is determined by the medium's compressibility and density . In solids, the compression waves are analogous to those in fluids, depending on compressibility and density, but with the additional factor of shear modulus which affects compression waves due to off-axis elastic energies which are able to influence effective tension and relaxation in a compression. The speed of shear waves, which can occur only in solids,

832-410: A computation of the speed of sound in air as 979 feet per second (298 m/s). This is too low by about 15%. The discrepancy is due primarily to neglecting the (then unknown) effect of rapidly fluctuating temperature in a sound wave (in modern terms, sound wave compression and expansion of air is an adiabatic process , not an isothermal process ). This error was later rectified by Laplace . During

936-571: A definite mathematical structure. The wave equation emerged in a number of contexts, including the propagation of sound in air. 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

1040-548: A key element of mating rituals or for 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. The word "acoustic" is derived from the Greek word ἀκουστικός ( akoustikos ), meaning "of or for hearing, ready to hear" and that from ἀκουστός ( akoustos ), "heard, audible", which in turn derives from

1144-497: A measure as employing an anechoic chamber , which absorbs nearly all sound. Another means is the use of devices such as earplugs , which are inserted into the ear canal to block noise, or earmuffs , objects designed to cover a person's ears entirely. The loss of hearing, when it is caused by neural loss, cannot presently be cured. Instead, its effects can be mitigated by the use of audioprosthetic devices, i.e. hearing assistive devices such as hearing aids and cochlear implants . In

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1248-486: A pipe aligned with the x {\displaystyle x} axis and with a cross-sectional area of A {\displaystyle A} . In time interval d t {\displaystyle dt} it moves length d x = v d t {\displaystyle dx=v\,dt} . In steady state , the mass flow rate m ˙ = ρ v A {\displaystyle {\dot {m}}=\rho vA} must be

1352-438: A range of normal hearing for both amplitude and frequency . Many animals use sound to communicate with each other, and hearing in these species is particularly important for survival and reproduction. In species that use sound as a primary means of communication, hearing is typically most acute for the range of pitches produced in calls and speech. Frequencies capable of being heard by humans are called audio or sonic. The range

1456-399: A result of varying auditory stimulus which can in turn affect the way one thinks, feels, or even behaves. This correlation can be viewed in normal, everyday situations in which listening to an upbeat or uptempo song can cause one's foot to start tapping or a slower song can leave one feeling calm and serene. In a deeper biological look at the phenomenon of psychoacoustics, it was discovered that

1560-405: A rock concert. The central stage in the acoustical process is wave propagation. This falls within the domain of physical acoustics. In fluids , sound propagates primarily as a pressure wave . In solids, mechanical waves can take many forms including longitudinal waves , transverse waves and surface waves . Acoustics looks first at the pressure levels and frequencies in the sound wave and how

1664-459: A single given gas (assuming the molecular weight does not change) and over a small temperature range (for which the heat capacity is relatively constant), the speed of sound becomes dependent on only the temperature of the gas. In non-ideal gas behavior regimen, for which the Van der Waals gas equation would be used, the proportionality is not exact, and there is a slight dependence of sound velocity on

1768-456: A sound wave to or from an electric signal. The most widely used transduction principles are electromagnetism , electrostatics and piezoelectricity . The transducers in most common loudspeakers (e.g. woofers and tweeters ), are electromagnetic devices that generate waves using a suspended diaphragm driven by an electromagnetic voice coil , sending off pressure waves. Electret microphones and condenser microphones employ electrostatics—as

1872-406: 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. Aristotle (384–322 BC) understood that sound consisted of compressions and rarefactions of air which "falls upon and strikes the air which

1976-438: 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 (echea) 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

2080-463: A way of echolocation in the caves. In archaeology, acoustic sounds and rituals directly correlate as specific sounds were meant to bring ritual participants closer to a spiritual awakening. Parallels can also be drawn between cave wall paintings and the acoustic properties of the cave; they are both dynamic. Because archaeoacoustics is a fairly new archaeological subject, acoustic sound is still being tested in these prehistoric sites today. Aeroacoustics

2184-413: Is filtered differently on its way into the ear depending on the location of its origin. This gives these animals the ability to localize sound vertically . The eardrum is an airtight membrane, and when sound waves arrive there, they cause it to vibrate following the waveform of the sound. Cerumen (ear wax) is produced by ceruminous and sebaceous glands in the skin of the human ear canal, protecting

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2288-513: Is affected as it moves through environments, e.g. underwater acoustics , architectural acoustics or structural acoustics . Other areas of work are listed under subdisciplines below. Acoustic scientists work in government, university and private industry laboratories. Many go on to work in Acoustical Engineering . Some positions, such as Faculty (academic staff) require a Doctor of Philosophy . Archaeoacoustics , also known as

2392-419: Is associated with compression and decompression in the direction of travel, and is the same process in gases and liquids, with an analogous compression-type wave in solids. Only compression waves are supported in gases and liquids. An additional type of wave, the transverse wave , also called a shear wave , occurs only in solids because only solids support elastic deformations. It is due to elastic deformation of

2496-417: Is called the object's Mach number . Objects moving at speeds greater than the speed of sound ( Mach 1 ) are said to be traveling at supersonic speeds . In Earth's atmosphere, the speed of sound varies greatly from about 295 m/s (1,060 km/h; 660 mph) at high altitudes to about 355 m/s (1,280 km/h; 790 mph) at high temperatures. Sir Isaac Newton 's 1687 Principia includes

2600-413: Is concerned with noise and vibration caused by railways, road traffic, aircraft, industrial equipment and recreational activities. The main aim of these studies is to reduce levels of environmental noise and vibration. Research work now also has a focus on the positive use of sound in urban environments: soundscapes and tranquility . Musical acoustics is the study of the physics of acoustic instruments;

2704-408: 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

2808-412: Is determined by the medium's compressibility , shear modulus , and density. The speed of shear waves is determined only by the solid material's shear modulus and density. In fluid dynamics , the speed of sound in a fluid medium (gas or liquid) is used as a relative measure for the speed of an object moving through the medium. The ratio of the speed of an object to the speed of sound (in the same medium)

2912-811: Is determined simply by the solid material's shear modulus and density. The speed of sound in mathematical notation is conventionally represented by c , from the Latin celeritas meaning "swiftness". For fluids in general, the speed of sound c is given by the Newton–Laplace equation: c = K s ρ , {\displaystyle c={\sqrt {\frac {K_{s}}{\rho }}},} where K s = ρ ( ∂ P ∂ ρ ) s {\displaystyle K_{s}=\rho \left({\frac {\partial P}{\partial \rho }}\right)_{s}} , where P {\displaystyle P}

3016-577: Is fully excited (i.e., molecular rotation is fully used as a heat energy "partition" or reservoir); but at the same time the temperature must be low enough that molecular vibrational modes contribute no heat capacity (i.e., insignificant heat goes into vibration, as all vibrational quantum modes above the minimum-energy-mode have energies that are too high to be populated by a significant number of molecules at this temperature). For air, these conditions are fulfilled at room temperature, and also temperatures considerably below room temperature (see tables below). See

3120-430: Is how our ears interpret sound. What we experience as "higher pitched" or "lower pitched" sounds are pressure vibrations having a higher or lower number of cycles per second. In a common technique of acoustic measurement, acoustic signals are sampled in time, and then presented in more meaningful forms such as octave bands or time frequency plots. Both of these popular methods are used to analyze sound and better understand

3224-624: Is next to it...", a very good expression of the nature of wave motion. On Things Heard , generally ascribed to Strato of Lampsacus , states that the pitch is related to the frequency of vibrations of the air and to the speed of sound. 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 . In Book V of his De architectura ( The Ten Books of Architecture ) Vitruvius describes sound as

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3328-462: Is not directly coupled with frequency range. Georg Von Békésy in 1929 identifying sound source directions suggested humans can resolve timing differences of 10μs or less. In 1976 Jan Nordmark's research indicated inter-aural resolution better than 2μs. Milind Kuncher's 2007 research resolved time misalignment to under 10μs. Even though they do not have ears, invertebrates have developed other structures and systems to decode vibrations traveling through

3432-425: Is performed primarily by the auditory system : mechanical waves , known as vibrations, are detected by the ear and transduced into nerve impulses that are perceived by the brain (primarily in the temporal lobe ). Like touch , audition requires sensitivity to the movement of molecules in the world outside the organism. Both hearing and touch are types of mechanosensation . There are three main components of

3536-442: Is the ability to perceive sounds through an organ, such as an ear , by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science . Sound may be heard through solid , liquid , or gaseous matter. It is one of the traditional five senses . Partial or total inability to hear is called hearing loss . In humans and other vertebrates, hearing

3640-414: Is the electronic manipulation of acoustic signals. Applications include: active noise control ; design for hearing aids or cochlear implants ; echo cancellation ; music information retrieval , and perceptual coding (e.g. MP3 or Opus ). Architectural acoustics (also known as building acoustics) involves the scientific understanding of how to achieve good sound within a building. It typically involves

3744-414: Is the main organ of mechanical to neural transduction . Inside the organ of Corti is the basilar membrane , a structure that vibrates when waves from the middle ear propagate through the cochlear fluid – endolymph . The basilar membrane is tonotopic , so that each frequency has a characteristic place of resonance along it. Characteristic frequencies are high at the basal entrance to the cochlea, and low at

3848-472: Is the pressure and the derivative is taken isentropically, that is, at constant entropy s . This is because a sound wave travels so fast that its propagation can be approximated as an adiabatic process , meaning that there isn't enough time, during a pressure cycle of the sound, for significant heat conduction and radiation to occur. Thus, the speed of sound increases with the stiffness (the resistance of an elastic body to deformation by an applied force) of

3952-429: Is the scientific study of the hearing and calls of animal calls, as well as how animals are affected by the acoustic and sounds of their habitat. This subdiscipline is concerned with the recording, manipulation and reproduction of audio using electronics. This might include products such as mobile phones , large scale public address systems or virtual reality systems in research laboratories. Environmental acoustics

4056-412: Is the study of noise generated by air movement, for instance via turbulence, and the movement of sound through the fluid air. This knowledge was applied in the 1920s and '30s to detect aircraft before radar was invented and is applied in acoustical engineering to study how to quieten aircraft . Aeroacoustics is important for understanding how wind musical instruments work. Acoustic signal processing

4160-430: Is the use of devices designed to prevent noise-induced hearing loss (NIHL), a type of post-lingual hearing impairment . The various means used to prevent hearing loss generally focus on reducing the levels of noise to which people are exposed. One way this is done is through environmental modifications such as acoustic quieting , which may be achieved with as basic a measure as lining a room with curtains , or as complex

4264-494: Is typically considered to be between 20 Hz and 20,000 Hz. Frequencies higher than audio are referred to as ultrasonic , while frequencies below audio are referred to as infrasonic . Some bats use ultrasound for echolocation while in flight. Dogs are able to hear ultrasound, which is the principle of 'silent' dog whistles . Snakes sense infrasound through their jaws, and baleen whales , giraffes , dolphins and elephants use it for communication. Some fish have

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4368-460: Is usually small, it is still noticeable to the human ear. The smallest sound that a person can hear, known as the threshold of hearing , is nine orders of magnitude smaller than the ambient pressure. The loudness of these disturbances is related to the sound pressure level (SPL) which is measured on a logarithmic scale in decibels. Physicists and acoustic engineers tend to discuss sound pressure levels in terms of frequencies, partly because this

4472-687: The audio signal processing used in electronic music; the computer analysis of music and composition, and the perception and cognitive neuroscience of music . The goal this acoustics sub-discipline is to reduce the impact of unwanted sound. Scope of noise studies includes the generation, propagation, and impact on structures, objects, and people. Noise research investigates the impact of noise on humans and animals to include work in definitions, abatement, transportation noise, hearing protection, Jet and rocket noise, building system noise and vibration, atmospheric sound propagation, soundscapes , and low-frequency sound. Many studies have been conducted to identify

4576-444: 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. 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

4680-506: The medial geniculate nucleus , a part of the thalamus where sound information is relayed to the primary auditory cortex in the temporal lobe . Sound is believed to first become consciously experienced at the primary auditory cortex . Around the primary auditory cortex lies Wernickes area , a cortical area involved in interpreting sounds that is necessary to understand spoken words. Disturbances (such as stroke or trauma ) at any of these levels can cause hearing problems, especially if

4784-446: The ozone layer . This produces a positive speed of sound gradient in this region. Still another region of positive gradient occurs at very high altitudes, in the thermosphere above 90 km . For an ideal gas, K (the bulk modulus in equations above, equivalent to C , the coefficient of stiffness in solids) is given by K = γ ⋅ p . {\displaystyle K=\gamma \cdot p.} Thus, from

4888-555: 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). Substantial progress in acoustics, resting on firmer mathematical and physical concepts, was made during the eighteenth century by Euler (1707–1783), Lagrange (1736–1813), and d'Alembert (1717–1783). During this era, continuum physics, or field theory, began to receive

4992-548: The springs , and the mass of the spheres. As long as the spacing of the spheres remains constant, stiffer springs/bonds transmit energy more quickly, while more massive spheres transmit energy more slowly. In a real material, the stiffness of the springs is known as the " elastic modulus ", and the mass corresponds to the material density . Sound will travel more slowly in spongy materials and faster in stiffer ones. Effects like dispersion and reflection can also be understood using this model. Some textbooks mistakenly state that

5096-614: The "One o'Clock Gun" is fired at the eastern end of Edinburgh Castle. Standing at the base of the western end of the Castle Rock, the sound of the Gun can be heard through the rock, slightly before it arrives by the air route, partly delayed by the slightly longer route. It is particularly effective if a multi-gun salute such as for "The Queen's Birthday" is being fired. In a gas or liquid, sound consists of compression waves. In solids, waves propagate as two different types. A longitudinal wave

5200-590: The 17th century there were several attempts to measure the speed of sound accurately, including attempts by Marin Mersenne in 1630 (1,380 Parisian feet per second), Pierre Gassendi in 1635 (1,473 Parisian feet per second) and Robert Boyle (1,125 Parisian feet per second). In 1709, the Reverend William Derham , Rector of Upminster, published a more accurate measure of the speed of sound, at 1,072 Parisian feet per second. (The Parisian foot

5304-415: 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

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5408-405: The Newton–Laplace equation above, the speed of sound in an ideal gas is given by c = γ ⋅ p ρ , {\displaystyle c={\sqrt {\gamma \cdot {p \over \rho }}},} where Using the ideal gas law to replace p with nRT / V , and replacing ρ with nM / V , the equation for an ideal gas becomes c i d e

5512-406: The ability to hear more sensitively due to a well-developed, bony connection between the ear and their swim bladder. This "aid to the deaf" for fishes appears in some species such as carp and herring . Human perception of audio signal time separation has been measured to less than 10 microseconds (10μs). This does not mean that frequencies above 100 kHz are audible, but that time discrimination

5616-461: The above diagram can be found in any acoustical event or process. There are many kinds of cause, both natural and volitional. There are many kinds of transduction process that convert energy from some other form into sonic energy, producing a sound wave. There is one fundamental equation that describes sound wave propagation, the acoustic wave equation , but the phenomena that emerge from it are varied and often complex. The wave carries energy throughout

5720-594: The acoustic phenomenon. The entire spectrum can be divided into three sections: audio, ultrasonic, and infrasonic. The audio range falls between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear. This range has a number of applications, including speech communication and music. The ultrasonic range refers to the very high frequencies: 20,000 Hz and higher. This range has shorter wavelengths which allow better resolution in imaging technologies. Medical applications such as ultrasonography and elastography rely on

5824-567: The air, or “sound”. Charles Henry Turner was the first scientist to formally show this phenomenon through rigorously controlled experiments in ants. Turner ruled out the detection of ground vibration and suggested that other insects likely have auditory systems as well. Many insects detect sound through the way air vibrations deflect hairs along their body. Some insects have even developed specialized hairs tuned to detecting particular frequencies, such as certain caterpillar species that have evolved hair with properties such that it resonates most with

5928-487: The apex. Basilar membrane motion causes depolarization of the hair cells , specialized auditory receptors located within the organ of Corti. While the hair cells do not produce action potentials themselves, they release neurotransmitter at synapses with the fibers of the auditory nerve , which does produce action potentials. In this way, the patterns of oscillations on the basilar membrane are converted to spatiotemporal patterns of firings which transmit information about

6032-427: The archaeology of sound, is one of the only ways to experience the past with senses other than our eyes. Archaeoacoustics is studied by testing the acoustic properties of prehistoric sites, including caves. Iegor Rezkinoff, a sound archaeologist, studies the acoustic properties of caves through natural sounds like humming and whistling. Archaeological theories of acoustics are focused around ritualistic purposes as well as

6136-491: The central nervous system is activated by basic acoustical characteristics of music. By observing how the central nervous system, which includes the brain and spine, is influenced by acoustics, the pathway in which acoustic affects the mind, and essentially the body, is evident. Acousticians study the production, processing and perception of speech. Speech recognition and Speech synthesis are two important areas of speech processing using computers. The subject also overlaps with

6240-438: 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

6344-456: The denser materials. An illustrative example of the two effects is that sound travels only 4.3 times faster in water than air, despite enormous differences in compressibility of the two media. The reason is that the greater density of water, which works to slow sound in water relative to the air, nearly makes up for the compressibility differences in the two media. For instance, sound will travel 1.59 times faster in nickel than in bronze, due to

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6448-535: The disciplines of physics, physiology , psychology , and linguistics . Structural acoustics is the study of motions and interactions of mechanical systems with their environments and the methods of their measurement, analysis, and control. There are several sub-disciplines found within this regime: Applications might include: ground vibrations from railways; vibration isolation to reduce vibration in operating theatres; studying how vibration can damage health ( vibration white finger ); vibration control to protect

6552-723: The disturbance is bilateral . In some instances it can also lead to auditory hallucinations or more complex difficulties in perceiving sound. Hearing can be measured by behavioral tests using an audiometer . Electrophysiological tests of hearing can provide accurate measurements of hearing thresholds even in unconscious subjects. Such tests include auditory brainstem evoked potentials (ABR), otoacoustic emissions (OAE) and electrocochleography (ECochG). Technical advances in these tests have allowed hearing screening for infants to become widespread. Hearing can be measured by mobile applications which includes audiological hearing test function or hearing aid application . These applications allow

6656-414: The ear canal and tympanic membrane from physical damage and microbial invasion. The middle ear consists of a small air-filled chamber that is located medial to the eardrum. Within this chamber are the three smallest bones in the body, known collectively as the ossicles which include the malleus, incus, and stapes (also known as the hammer, anvil, and stirrup, respectively). They aid in the transmission of

6760-445: The fastest it can travel under normal conditions. In theory, the speed of sound is actually the speed of vibrations. Sound waves in solids are composed of compression waves (just as in gases and liquids) and a different type of sound wave called a shear wave , which occurs only in solids. Shear waves in solids usually travel at different speeds than compression waves, as exhibited in seismology . The speed of compression waves in solids

6864-456: 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. Acoustics

6968-477: The gas pressure. Humidity has a small but measurable effect on the speed of sound (causing it to increase by about 0.1%–0.6%), because oxygen and nitrogen molecules of the air are replaced by lighter molecules of water . This is a simple mixing effect. In the Earth's atmosphere , the chief factor affecting the speed of sound is the temperature . For a given ideal gas with constant heat capacity and composition,

7072-615: The greater stiffness of nickel at about the same density. Similarly, sound travels about 1.41 times faster in light hydrogen ( protium ) gas than in heavy hydrogen ( deuterium ) gas, since deuterium has similar properties but twice the density. At the same time, "compression-type" sound will travel faster in solids than in liquids, and faster in liquids than in gases, because the solids are more difficult to compress than liquids, while liquids, in turn, are more difficult to compress than gases. A practical example can be observed in Edinburgh when

7176-401: The ground, creating an acoustic shadow at some distance from the source. The decrease of the speed of sound with height is referred to as a negative sound speed gradient . However, there are variations in this trend above 11 km . In particular, in the stratosphere above about 20 km , the speed of sound increases with height, due to an increase in temperature from heating within

7280-413: The gunshot with a half-second pendulum. Measurements were made of gunshots from a number of local landmarks, including North Ockendon church. The distance was known by triangulation , and thus the speed that the sound had travelled was calculated. The transmission of sound can be illustrated by using a model consisting of an array of spherical objects interconnected by springs. In real material terms,

7384-401: The human auditory system : the outer ear, the middle ear, and the inner ear. The outer ear includes the pinna , the visible part of the ear, as well as the ear canal , which terminates at the eardrum , also called the tympanic membrane. The pinna serves to focus sound waves through the ear canal toward the eardrum. Because of the asymmetrical character of the outer ear of most mammals, sound

7488-466: The important factors, since fluids do not transmit shear stresses. In heterogeneous fluids, such as a liquid filled with gas bubbles, the density of the liquid and the compressibility of the gas affect the speed of sound in an additive manner, as demonstrated in the hot chocolate effect . In gases, adiabatic compressibility is directly related to pressure through the heat capacity ratio (adiabatic index), while pressure and density are inversely related to

7592-415: The inner ear through the oval window , a flexible membrane separating the air-filled middle ear from the fluid-filled inner ear. The round window , another flexible membrane, allows for the smooth displacement of the inner ear fluid caused by the entering sound waves. The inner ear consists of the cochlea , which is a spiral-shaped, fluid-filled tube. It is divided lengthwise by the organ of Corti , which

7696-473: The material and decreases with an increase in density. For ideal gases, the bulk modulus K is simply the gas pressure multiplied by the dimensionless adiabatic index , which is about 1.4 for air under normal conditions of pressure and temperature. For general equations of state , if classical mechanics is used, the speed of sound c can be derived as follows: Consider the sound wave propagating at speed v {\displaystyle v} through

7800-563: The medium perpendicular to the direction of wave travel; the direction of shear-deformation is called the " polarization " of this type of wave. In general, transverse waves occur as a pair of orthogonal polarizations. These different waves (compression waves and the different polarizations of shear waves) may have different speeds at the same frequency. Therefore, they arrive at an observer at different times, an extreme example being an earthquake , where sharp compression waves arrive first and rocking transverse waves seconds later. The speed of

7904-451: The medium through which a sound wave is propagating. At 0 °C (32 °F), the speed of sound in air is about 331 m/s (1,086 ft/s; 1,192 km/h; 740 mph; 643 kn). The speed of sound in an ideal gas depends only on its temperature and composition. The speed has a weak dependence on frequency and pressure in ordinary air, deviating slightly from ideal behavior. In colloquial speech, speed of sound refers to

8008-544: The more desirable, harmonious notes. During the Islamic golden age , Abū Rayhān al-Bīrūnī (973–1048) is believed to have postulated that the speed of sound was much slower than the speed of light. 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

8112-406: The propagating medium. Eventually this energy is transduced again into other forms, in ways that again may be natural and/or volitionally contrived. The final effect may be purely physical or it may reach far into the biological or volitional domains. The five basic steps are found equally well whether we are talking about an earthquake , a submarine using sonar to locate its foe, or a band playing in

8216-432: The properties of the substance through which the wave is travelling. In solids, the speed of transverse (or shear) waves depends on the shear deformation under shear stress (called the shear modulus ), and the density of the medium. Longitudinal (or compression) waves in solids depend on the same two factors with the addition of a dependence on compressibility . In fluids, only the medium's compressibility and density are

8320-434: The relationship between acoustics and cognition , or more commonly known as psychoacoustics , in which what one hears is a combination of perception and biological aspects. The information intercepted by the passage of sound waves through the ear is understood and interpreted through the brain, emphasizing the connection between the mind and acoustics. Psychological changes have been seen as brain waves slow down or speed up as

8424-1421: The same at the two ends of the tube, therefore the mass flux j = ρ v {\displaystyle j=\rho v} is constant and v d ρ = − ρ d v {\displaystyle v\,d\rho =-\rho \,dv} . Per Newton's second law , the pressure-gradient force provides the acceleration: d v d t = − 1 ρ d P d x → d P = ( − ρ d v ) d x d t = ( v d ρ ) v → v 2 ≡ c 2 = d P d ρ {\displaystyle {\begin{aligned}{\frac {dv}{dt}}&=-{\frac {1}{\rho }}{\frac {dP}{dx}}\\[1ex]\rightarrow dP&=(-\rho \,dv){\frac {dx}{dt}}=(v\,d\rho )v\\[1ex]\rightarrow v^{2}&\equiv c^{2}={\frac {dP}{d\rho }}\end{aligned}}} And therefore: c = ( ∂ P ∂ ρ ) s = K s ρ , {\displaystyle c={\sqrt {\left({\frac {\partial P}{\partial \rho }}\right)_{s}}}={\sqrt {\frac {K_{s}}{\rho }}},} If relativistic effects are important,

8528-466: The section on gases in specific heat capacity for a more complete discussion of this phenomenon. For air, we introduce the shorthand R ∗ = R / M a i r . {\displaystyle R_{*}=R/M_{\mathrm {air} }.} In addition, we switch to the Celsius temperature θ = T − 273.15 K , which is useful to calculate air speed in

8632-483: The sound of buzzing wasps, thus warning them of the presence of natural enemies. Some insects possess a tympanal organ . These are "eardrums", that cover air filled chambers on the legs. Similar to the hearing process with vertebrates, the eardrums react to sonar waves. Receptors that are placed on the inside translate the oscillation into electric signals and send them to the brain. Several groups of flying insects that are preyed upon by echolocating bats can perceive

8736-474: The sound to the brainstem . The sound information from the cochlea travels via the auditory nerve to the cochlear nucleus in the brainstem . From there, the signals are projected to the inferior colliculus in the midbrain tectum . The inferior colliculus integrates auditory input with limited input from other parts of the brain and is involved in subconscious reflexes such as the auditory startle response . The inferior colliculus in turn projects to

8840-426: The sound wave is a small perturbation on the ambient condition, and the certain other noted conditions are fulfilled, as noted below. Calculated values for c air have been found to vary slightly from experimentally determined values. Newton famously considered the speed of sound before most of the development of thermodynamics and so incorrectly used isothermal calculations instead of adiabatic . His result

8944-443: The sound wave strikes the microphone's diaphragm, it moves and induces a voltage change. The ultrasonic systems used in medical ultrasonography employ piezoelectric transducers. These are made from special ceramics in which mechanical vibrations and electrical fields are interlinked through a property of the material itself. An acoustician is an expert in the science of sound. There are many types of acoustician, but they usually have

9048-404: The speed of sound increases with density. This notion is illustrated by presenting data for three materials, such as air, water, and steel and noting that the speed of sound is higher in the denser materials. But the example fails to take into account that the materials have vastly different compressibility, which more than makes up for the differences in density, which would slow wave speeds in

9152-423: The speed of sound is about 75% of the mean speed that the atoms move in that gas. For a given ideal gas the molecular composition is fixed, and thus the speed of sound depends only on its temperature . At a constant temperature, the gas pressure has no effect on the speed of sound, since the density will increase, and since pressure and density (also proportional to pressure) have equal but opposite effects on

9256-506: The speed of sound is calculated from the relativistic Euler equations . In a non-dispersive medium , the speed of sound is independent of sound frequency , so the speeds of energy transport and sound propagation are the same for all frequencies. Air, a mixture of oxygen and nitrogen, constitutes a non-dispersive medium. However, air does contain a small amount of CO 2 which is a dispersive medium, and causes dispersion to air at ultrasonic frequencies (greater than 28  kHz ). In

9360-404: The speed of sound is dependent solely upon temperature; see § Details below. In such an ideal case, the effects of decreased density and decreased pressure of altitude cancel each other out, save for the residual effect of temperature. Since temperature (and thus the speed of sound) decreases with increasing altitude up to 11 km , sound is refracted upward, away from listeners on

9464-539: The speed of sound waves in air . However, the speed of sound varies from substance to substance: typically, sound travels most slowly in gases , faster in liquids , and fastest in solids . For example, while sound travels at 343 m/s in air, it travels at 1481 m/s in water (almost 4.3 times as fast) and at 5120 m/s in iron (almost 15 times as fast). In an exceptionally stiff material such as diamond, sound travels at 12,000 m/s (39,370 ft/s),  – about 35 times its speed in air and about

9568-490: The speed of sound, and the two contributions cancel out exactly. In a similar way, compression waves in solids depend both on compressibility and density—just as in liquids—but in gases the density contributes to the compressibility in such a way that some part of each attribute factors out, leaving only a dependence on temperature, molecular weight, and heat capacity ratio which can be independently derived from temperature and molecular composition (see derivations below). Thus, for

9672-402: The spheres represent the material's molecules and the springs represent the bonds between them. Sound passes through the system by compressing and expanding the springs, transmitting the acoustic energy to neighboring spheres. This helps transmit the energy in-turn to the neighboring sphere's springs (bonds), and so on. The speed of sound through the model depends on the stiffness /rigidity of

9776-466: The study of speech intelligibility, speech privacy, music quality, and vibration reduction in the built environment. Commonly studied environments are hospitals, classrooms, dwellings, performance venues, recording and broadcasting studios. Focus considerations include room acoustics, airborne and impact transmission in building structures, airborne and structure-borne noise control, noise control of building systems and electroacoustic systems. Bioacoustics

9880-429: The temperature and molecular weight, thus making only the completely independent properties of temperature and molecular structure important (heat capacity ratio may be determined by temperature and molecular structure, but simple molecular weight is not sufficient to determine it). Sound propagates faster in low molecular weight gases such as helium than it does in heavier gases such as xenon . For monatomic gases,

9984-456: The time varying pressure level and frequency profiles which give a specific acoustic signal its defining character. 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 sonar projectors. These devices convert

10088-420: The ultrasonic frequency range. On the other end of the spectrum, the lowest frequencies are known as the infrasonic range. These frequencies can be used to study geological phenomena such as earthquakes. Analytic instruments such as the spectrum analyzer facilitate visualization and measurement of acoustic signals and their properties. The spectrogram produced by such an instrument is a graphical display of

10192-563: The ultrasound emissions this way and reflexively practice ultrasound avoidance . Speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air is about 343  m/s (1,125  ft/s ; 1,235  km/h ; 767  mph ; 667  kn ), or 1  km in 2.91 s or one mile in 4.69 s . It depends strongly on temperature as well as

10296-498: The user to measure hearing thresholds at different frequencies ( audiogram ). Despite possible errors in measurements, hearing loss can be detected. There are several different types of hearing loss: conductive hearing loss , sensorineural hearing loss and mixed types. Recently, the term of Aural Diversity has come into greater use, to communicate hearing loss and differences in a less negatively-associated term. There are defined degrees of hearing loss: Hearing protection

10400-497: The verb ἀκούω( akouo ), "I hear". The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics and later a branch of acoustics. Frequencies above and below the audible range are called " ultrasonic " and " infrasonic ", respectively. 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

10504-408: The vibrations from the eardrum into the inner ear, the cochlea . The purpose of the middle ear ossicles is to overcome the impedance mismatch between air waves and cochlear waves, by providing impedance matching . Also located in the middle ear are the stapedius muscle and tensor tympani muscle , which protect the hearing mechanism through a stiffening reflex. The stapes transmits sound waves to

10608-416: The wave interacts with the environment. This interaction can be described as either a diffraction , interference or a reflection or a mix of the three. If several media are present, a refraction can also occur. Transduction processes are also of special importance to acoustics. In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. While this disturbance

10712-422: Was 325 mm . This is longer than the standard "international foot" in common use today, which was officially defined in 1959 as 304.8 mm , making the speed of sound at 20 °C (68 °F) 1,055 Parisian feet per second). Derham used a telescope from the tower of the church of St. Laurence, Upminster to observe the flash of a distant shotgun being fired, and then measured the time until he heard

10816-435: Was missing the factor of γ but was otherwise correct. Numerical substitution of the above values gives the ideal gas approximation of sound velocity for gases, which is accurate at relatively low gas pressures and densities (for air, this includes standard Earth sea-level conditions). Also, for diatomic gases the use of γ = 1.4000 requires that the gas exists in a temperature range high enough that rotational heat capacity

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