Acoustics is a branch of physics and is the study of sound, mechanical waves in gases, liquids, and solids. A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers. The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. ... A schematic representation of auditory signaling Sound is vibration, as perceived by the sense of hearing. ... The WAVES were a World War II era division of the U.S. Navy that consisted entirely of women. ... Gas (actually, as), the GNU assembler, is the default GCC back-end. ... HI LIQUIDX ^_^ Your name is now immortalised within the realms of Wikipedia! A liquid will assume the shape of its container. ... A solid is a state of matter, characterized by a definite volume and a definite shape (i. ... Technology (Gr. ... Acoustical engineering is the branch of engineering dealing with sound and vibration. ...

"... acoustics is characterized by its reliance on combinations of physical principles drawn from other sources; and that the primary task of modern physical acoustics is to effect a fusion of the principles normally adhering to other sciences into a coherent basis for understanding, measuring, controlling, and using the whole gamut of vibrational phenomena in any material medium." Origins in Acoustics. F.V. Hunt. Yale University Press, 1978

The main sub-disciplines of acoustics are

• Aeroacoustics is the study of aerodynamic sound, generated when a fluid flow interacts with a solid surface or with another flow. It has particular application to aeronautics, examples being the study of sound made by jets and the physics of shock waves (sonic booms).

• Architectural acoustics is the study of how sound and buildings interact including the behavior of sound in concert halls and auditoriums but also in office buildings, factories and homes.

• Bioacoustics is the study of the use of sound by animals such as whales, dolphins and bats.

• Biomedical acoustics is the study of the use of sound in medicine, for example the use of ultrasound for diagnostic and therapeutic purposes.

• Loudspeaker acoustics is an engineering discipline behind the design of the loudspeaker

• Psychoacoustics is the study of how people react to sound, hearing, perception, and localization.

• Physiological acoustics is the study of the mechanical, electrical and biochemical function of hearing in living organisms.

• Physical acoustics is the study of the detailed interaction of sound with materials and fluids and includes, for example, sonoluminescence (the emission of light by bubbles in a liquid excited by sound) and thermoacoustics (the interaction of sound and heat).

• Speech communication is the study of how speech is produced, the analysis of speech signals and the properties of speech transmission, storage, recognition and enhancement.

• Vibration acoustics Structural Acoustics and Vibration is the study of how sound and mechanical structures interact and includes the transmission of sound through walls and the radiation of sound from vehicle panels.

• Ultrasonics is the study of high frequency sound, beyond the range of human hearing.

• Musical acoustics is the study of the physics of musical instruments

• Underwater acoustics is the study of the propagation of sound in the oceans. Closely associated with sonar research and development.

• Acoustic engineering is the study of how sound is generated and measured by loudspeakers, microphones, sonar projectors, hydrophones, ultrasonic transducers, sensors, Electro Acoustics, and all other topics on this list. (see external links)

A sound wave is characterized by its speed, its wavelength and its amplitude. The speed of sound depends on the medium through which the sound travels and also depends on temperature and not on the air pressure. The speed of sound is about 340 m/s in air and 1500 m/s in water. The wavelength is the distance from one wave peak to the next. The wavelength, λ of a sound wave is related to the speed of sound c and its frequency f by A schematic representation of auditory signaling Sound is vibration, as perceived by the sense of hearing. ... Aeronautics is the science and practice of aerial locomotion, i. ... In fluid dynamics, a shock wave is a nonlinear pressure wave. ... Architectural acoustics is the science of controlling quality of sound in buildings. ... A Concert hall is a cultural building, which serves as performance venue, chiefly for classical instrumental music. ... Bioacoustics is the study of how animals, use sound for communication and echolocation. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria Acoelomorpha Orthonectida Rhombozoa Myxozoa Superphylum Deuterostomia    Chordata (vertebrates, etc. ... Whales are the largest species of exclusively aquatic placental mammals, members of the order Cetacea, which also includes dolphins and porpoises. ... Genera See article below. ... Families Pteropodidae Emballonuridae Rhinopomatidae Craseonycteridae Rhinolophidae Nycteridae Megadermatidae Vespertilionidae Molossidae Antrozoidae Natalidae Myzopodidae Thyropteridae Furipteridae Noctilionidae Mystacinidae Mormoopidae Phyllostomidae Bats are flying mammals in the order Chiroptera with forelimbs developed as wings. ... Medicine is a branch of health science concerned with maintaining health and restoring it by treating disease. ... Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ... Loudspeaker Acoustics is the study (either scientific or pseudo-scientific) of the behaviour of the loudspeaker and in particular the effort to create loudspeakers with good sound quality (either subjectively or objectively measured). ... Closeup of a loudspeaker driver A loudspeaker is a device which converts an electrical signal into sound. ... Psychoacoustics is the study of subjective human perception of sounds. ... Hearing is one, the auditory, of the traditional five senses, and refers to the ability to detect sound. ... In psychology and the cognitive sciences, perception is the process of acquiring, interpreting, selecting, and organizing sensory information. ... Sound localization is a listeners ability to identify the location of origin of a detected sound or the methods in acoustical engineering to simulate the placement of an auditory cue in a virtual 3D space (see binaural recording). ... Hearing is the following: Hearing is the sense by which sound is perceived. ... Sonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound. ... Thermoacoustics is the use of sound waves to affect temperature. ... Speech: (n. ... Radiation of sound should not be confused with propagation of sound. ... Vehicles are non-living means of transport. ... Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... Musical acoustics or music acoustics is the branch of acoustics concerned with researching and describing the physics of music — how sounds employed as music work. ... A musical instrument is a device that has been constructed or modified with the purpose of making music. ... Ocean (from Okeanos, a Greek god of sea and water; Greek ωκεανός) covers almost three quarters (71%) of the surface of the Earth. ... The F70 type frigates (here, La Motte-Picquet) are fitted with VDS (Variable Depth Sonar) type DUBV43 or DUBV43C tugged sonars Sonar (sound navigation and ranging) is a technique that uses sound propagation under water to navigate or to detect other watercraft. ... Acoustical engineering is the branch of engineering dealing with sound and vibration. ... Closeup of a loudspeaker driver A loudspeaker is a device which converts an electrical signal into sound. ... A microphone with a cord A microphone, sometimes called a mic (pronounced mike), is a device that converts sound into an electrical signal. ... A hydrophone is a sound-to-electricity transducer for use in water or other liquids, analogous to a microphone for air. ... A sensor is a technological device or biological organ that detects, or senses, a signal or physical condition. ... The wavelength is the distance between repeating units of a wave pattern. ... The speed of sound varies depending on the medium through which the sound waves pass. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ...

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Sound pressure level (SPL)

The amplitude of a sound wave is most commonly characterized by its sound pressure. In a normal working environment, a very wide range of pressures can occur and it is therefore a convention that sound pressure is measured on a logarithmic scale using the decibel. If p is the rms sound pressure amplitude then the sound pressure level (SPL) is defined as 20 times the logarithm of the ratio of the pressure to some reference pressure. Amplitude is a nonnegative scalar measure of a waves magnitude of oscillation. ... Sound pressure p (or acoustic pressure) is the measurement in pascals of the root mean square (RMS) pressure deviation (from atmospheric pressure) caused by a sound wave passing through a fixed point. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ... In mathematics, if two variables of bn = x are known, the third can be found. ... Although it is widely used as a measure of the loudness of sound, the decibel is more generally a measure of the ratio between two quantities, and can be used to express a wide variety of measurements in acoustics and electronics. ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the energy of a particular noise relative to a reference noise source. ...

Sound pressure level SPL is calculated in decibels as Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the energy of a particular noise relative to a reference noise source. ... Although it is widely used as a measure of the loudness of sound, the decibel is more generally a measure of the ratio between two quantities, and can be used to express a wide variety of measurements in acoustics and electronics. ...

The reference sound pressure in air is by convention the threshold of hearing: Threshold of hearing is the sound pressure level SPL of 20 µPa (micropascal) = 2 × 10-5 Pascal (Pa). ...

= 20 µPa in air and 1 µPa in water. (Pa = pascal = N / m²; N = newton)

When speaking of sound levels, one must be sure to differentiate between sound pressure levels and sound power levels. Sound pressure levels are recorded by microphones and other devices. This is a measurement of the amount of pressure in the air being sensed at a given location. It follows that its value can be determined through direct experimentation. In comparison, sound power levels are a measurement of the actual energy being put into use by a given device to create noise. Because of environmental factors, and other influences, the amount of energy a device devotes to creating sound may not be equal to the actual level of the sound as it's perceived. It can be useful to express sound pressure in this way when dealing with hearing, as the perceived loudness of a sound correlates roughly logarithmically to its sound pressure. Both microphones and eardrums respond to the sound pressure level. They cannot convert the sound intensity. Sound power measurements cannot be directly measured, and must be inferred through other data. The pascal (symbol Pa) is the SI unit of pressure. ... In physics, the newton (symbol: N) is the SI unit of force, named after Sir Isaac Newton in recognition of his work on classical mechanics. ... Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the energy of a particular noise relative to a reference noise source. ... A microphone with a cord A microphone, sometimes called a mic (pronounced mike), is a device that converts sound into an electrical signal. ... Mechanical power In physics, power (symbol: P) is the amount of work W done per unit of time t. ... In general usage, noise can be considered data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. ... Hearing is one, the auditory, of the traditional five senses, and refers to the ability to detect sound. ... The sound intensity, J, (acoustic intensity) is defined as the sound power Pac per unit area A. The usual context is the measurement of sound intensity in the air at a listeners location. ...

Measurement methods

There are two popular ways for scientists to perform acoustical measurements. They include a "direct method", and a "comparison method". The direct method computes sound power levels by computing an equation of environmental factors (such as room temperature, humidity, reverberation time, etc.) and sound pressure levels. A more precise implementation of this method can be found in the ISO3745 acoustics standard. The comparison method however, is conducted by measuring sound pressure levels from a reference sound source which emits a known, constant, sound power level, and then comparing that level with the sound pressure level of the object being recorded. Each way is equally valid and accurate. Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... Humidity is the quantity of moisture in the air. ... When sound is produced in an enclosed space multiple reflections build up and blend together creating reverberation or reverb. ... In general, a reference is something that refers or points to something else, or acts as a connection or a link between two things. ...

Reverberation and anechoic rooms

Experiments such as the two methods mentioned above are sometimes performed in reverberation rooms, or in some cases, anechoic rooms. The design of a reverberation room is to create long lasting echoes of sound waves. This helps create a highly averaged and omnidirectional sound level throughout the entire chamber. A typical example of rooms with characteristics similar to reverberation rooms are concrete tunnels, caves, etc. Anechoic rooms, such as hemi-anechoic rooms, or fully anechoic rooms are created to simulate what is called a free field. A free field is the representation of a theoretical infinite space, in which no sound wave reflections, or echoes, take place. In rooms such as these, the only sounds which exist are being emitted directly from the source, and are not reflected from another part of the chamber. Anechoic rooms have the characteristic of being muted and muffled. Reverberation Chamber is a acoustically designed room for uniform distribution of acoustic energy. ... An anechoic room simulates a free field — a representation of a theoretical infinite space, in which there are no sound wave reflections (echoes). ... In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. ... Classically, a free field is a field described by linear partial differential equations which has a unique solution given initial data. ... The reflection of sunlight on water Reflection is the abrupt change in direction of a wave front at an interface between two dissimilar media so that the wave front returns into the medium from which it originated. ...

Helmholtz resonator

A Helmholtz resonator is a container with an open hole or neck. It is sometimes used as a passive noise control device.

• f = resonant frequency
• s = speed of sound in air
• r = radius of neck
• a = area of neck
• l = length of neck
• L′ = effective length of neck

L′ = l + 1.7r (outer end flanged)

L′ = l + 1.4r (outer end unflanged)

• v = volume

The Helmholtz resonator is an example of the lumped component model of acoustic systems which is useful when the wavelength of interest is significantly larger than the physical dimensions of the system. Lumped component model In general, the lumped component model is a way of simplifying the behaviour of spacially distributed systems into a topology consisting of discrete entities that approximate the behaviour of the distributed system under certain assumptions. ... The wavelength is the distance between repeating units of a wave pattern. ...

Rectangular boxes

• f = frequency of standing wave of a rectangular box
• s = speed of sound in air
• x,y,z = dimensions of box
• N_x,N_y,N_z = any integers

See also

More specialized areas of acoustics include, but are not limited to, tonal analysis, sound quality assessments, and noise control.

Subfields and related fields of acoustics:

• Acoustic theory
• Structural acoustics
• Noise control
• Room acoustics
• Concert hall acoustics
• Musical instruments
• Underwater acoustics
• Audio signal processing
  • Audio storage
  • Sound synthesis
  • Speech processing
• Psychoacoustics
• Important publications in acoustics

Acoustic theory is the field relating to mathematical description of sound waves. ... Room acoustics describes how sound behaves in an enclosed space. ... A musical instrument is a device that has been constructed or modified with the purpose of making music. ... Audio signal processing, sometimes referred to as audio processing, is the processing of a representation of auditory signals, or sound. ... Audio storage refers to techniques and formats used to store audio with the goal to reproduce the audio later using audio signal processing to something that resembles the original. ... The term synthesiser is also used to mean frequency synthesiser, an electronic system found in communications. ... Speech processing is the study of speech signals and the processing methods of these signals. ... Psychoacoustics is the study of subjective human perception of sounds. ... This is a list of important publications in physics, organized by field. ...

External links

• Helmholtz Resonator (http://physics.kenyon.edu/EarlyApparatus/Rudolf_Koenig_Apparatus/Helmholtz_Resonator/Helmholtz_Resonator.html)
• Helmholtz Resonance (http://www.phys.unsw.edu.au/~jw/Helmholtz.html)
• Helmholtz Resonator with oscilloscope (http://www.physics.umd.edu/lecdem/services/demos/demosh3/h3-41.htm)
• Acoustic Engineering at Universidad Austral de Chile (http://www.fci.uach.cl/escuela/ingacustica/index.htm)
• Sounds Amazing: a learning resource for sound and waves (http://www.acoustics.salford.ac.uk/schools/index.htm)