Acoustical engineering (also known as acoustic engineering ) is the branch of engineering dealing with sound and vibration . It includes the application of acoustics , the science of sound and vibration, in technology. Acoustical engineers are typically concerned with the design, analysis and control of sound.
119-406: One goal of acoustical engineering can be the reduction of unwanted noise, which is referred to as noise control . Unwanted noise can have significant impacts on animal and human health and well-being, reduce attainment by students in schools, and cause hearing loss. Noise control principles are implemented into technology and design in a variety of ways, including control by redesigning sound sources,
238-482: A Doctor of Philosophy . In most countries, a degree in acoustics can represent the first step towards professional certification and the degree program may be certified by a professional body . After completing a certified degree program the engineer must satisfy a range of requirements before being certified. Once certified, the engineer is designated the title of Chartered Engineer (in most Commonwealth countries). The listed subdisciplines are loosely based on
357-824: A bachelor's degree or higher qualification in acoustics , physics or another engineering discipline. Practicing as an acoustic engineer usually requires a bachelor's degree with significant scientific and mathematical content. Acoustic engineers might work in acoustic consultancy, specializing in particular fields, such as architectural acoustics , environmental noise or vibration control . In other industries, acoustic engineers might: design automobile sound systems; investigate human response to sounds, such as urban soundscapes and domestic appliances; develop audio signal processing software for mixing desks, and design loudspeakers and microphones for mobile phones. Acousticians are also involved in researching and understanding sound scientifically. Some positions, such as faculty require
476-435: A caveat for a version using a brass rod instead of the needle. Other minor variations and improvements were made to the liquid microphone by Majoranna, Chambers, Vanni, Sykes, and Elisha Gray, and one version was patented by Reginald Fessenden in 1903. These were the first working microphones, but they were not practical for commercial application. The famous first phone conversation between Bell and Watson took place using
595-489: A computer model to calculate sound levels has become standard practice since the early 1970s. In this way exposure of sensitive receptors to elevated sound levels can be minimized. An analogous process exists for urban mass transit systems and other rail transportation decisions. Early examples of urban rail systems designed using this technology were: Boston MBTA line expansions (1970s), San Francisco BART system expansion (1981), Houston METRORail system (1982), and
714-713: A mic ( / m aɪ k / ), or mike , is a transducer that converts sound into an electrical signal . Microphones are used in many applications such as telephones , hearing aids , public address systems for concert halls and public events, motion picture production, live and recorded audio engineering , sound recording , two-way radios , megaphones , and radio and television broadcasting. They are also used in computers and other electronic devices, such as mobile phones , for recording sounds, speech recognition , VoIP , and other purposes, such as ultrasonic sensors or knock sensors . Several types of microphone are used today, which employ different methods to convert
833-403: A resonant circuit that modulates the frequency of the oscillator signal. Demodulation yields a low-noise audio frequency signal with a very low source impedance. The absence of a high bias voltage permits the use of a diaphragm with looser tension, which may be used to achieve wider frequency response due to higher compliance. The RF biasing process results in a lower electrical impedance capsule,
952-527: A surround sound system. "Psychoacoustics seeks to reconcile acoustical stimuli and all the scientific, objective, and physical properties that surround them, with the physiological and psychological responses evoked by them." Speech is a major area of study for acoustical engineering, including the production, processing and perception of speech. This can include physics , physiology , psychology , audio signal processing and linguistics . Speech recognition and speech synthesis are two important aspects of
1071-592: A 3.5 mm plug as usually used for stereo connections; the ring, instead of carrying the signal for a second channel, carries power. A valve microphone is a condenser microphone that uses a vacuum tube (valve) amplifier . They remain popular with enthusiasts of tube sound . The dynamic microphone (also known as the moving-coil microphone ) works via electromagnetic induction . They are robust, relatively inexpensive and resistant to moisture. This, coupled with their potentially high gain before feedback , makes them popular for on-stage use. Dynamic microphones use
1190-457: A button microphone), uses a capsule or button containing carbon granules pressed between two metal plates like the Berliner and Edison microphones. A voltage is applied across the metal plates, causing a small current to flow through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident sound waves, applying a varying pressure to the carbon. The changing pressure deforms
1309-429: A combination of sound absorption materials, arrays of microphones and speakers, and a digital processor, a restaurant operator can use a tablet computer to selectively control noise levels at different places in the restaurant: the microphone arrays pick up sound and send it to the digital processor, which controls the speakers to output sound signals on command. Post-construction residential acoustic treatment throughout
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#17328024751391428-441: A diaphragm that is at least partially open on both sides. The pressure difference between the two sides produces its directional characteristics. Other elements such as the external shape of the microphone and external devices such as interference tubes can also alter a microphone's directional response. A pure pressure-gradient microphone is equally sensitive to sounds arriving from front or back but insensitive to sounds arriving from
1547-615: A few decibels and would be barely noticeable. Highway noise is today less affected by motor type, since the effects in higher speed are aerodynamic and tire noise related. Other contributions to the reduction of noise at the source are: improved tire tread designs for trucks in the 1970s, better shielding of diesel stacks in the 1980s, and local vehicle regulation of unmuffled vehicles. The most fertile areas for roadway noise mitigation are in urban planning decisions, roadway design, noise barrier design, speed control, surface pavement selection, and truck restrictions. Speed control
1666-435: A high-quality audio signal and are now the popular choice in laboratory and recording studio applications. The inherent suitability of this technology is due to the very small mass that must be moved by the incident sound wave compared to other microphone types that require the sound wave to do more work. Condenser microphones require a power source, provided either via microphone inputs on equipment as phantom power or from
1785-506: A host of alternative strategies. In Canada, Transport Canada prepares noise exposure forecasts (NEF) for each airport, using a computer model similar to that used in the US. Residential land development is discouraged within high impact areas identified by the forecast. Architectural acoustics noise control practices include interior sound reverberation reduction, inter-room noise transfer mitigation, and exterior building skin augmentation. In
1904-590: A host of specialized means for damping reverberation from special-purpose rooms such as auditoria , concert halls , entertainment and social venues, dining areas, audio recording rooms, and meeting rooms. Many of these techniques rely upon material science applications of constructing sound baffles or using sound-absorbing liners for interior spaces. Industrial noise control is a subset of interior architectural control of noise, with emphasis on specific methods of sound isolation from industrial machinery and for protection of workers at their task stations. Sound masking
2023-492: A laser source travels through an optical fiber to illuminate the surface of a reflective diaphragm. Sound vibrations of the diaphragm modulate the intensity of light reflecting off the diaphragm in a specific direction. The modulated light is then transmitted over a second optical fiber to a photodetector, which transforms the intensity-modulated light into analog or digital audio for transmission or recording. Fiber-optic microphones possess high dynamic and frequency range, similar to
2142-546: A laser-photocell pair with a moving stream of smoke or vapor in the laser beam's path. Sound pressure waves cause disturbances in the smoke that in turn cause variations in the amount of laser light reaching the photodetector. A prototype of the device was demonstrated at the 127th Audio Engineering Society convention in New York City from 9 through October 12, 2009. Early microphones did not produce intelligible speech, until Alexander Graham Bell made improvements including
2261-453: A liquid microphone. The MEMS (microelectromechanical systems) microphone is also called a microphone chip or silicon microphone. A pressure-sensitive diaphragm is etched directly into a silicon wafer by MEMS processing techniques and is usually accompanied with an integrated preamplifier. Most MEMS microphones are variants of the condenser microphone design. Digital MEMS microphones have built-in analog-to-digital converter (ADC) circuits on
2380-412: A negative surface texture and use small to medium-sized aggregates; the loudest pavements have transversely-grooved surfaces, positive surface textures, and larger aggregates. Surface friction and roadway safety are important considerations as well for pavement decisions. When designing new urban freeways or arterials, there are numerous design decisions regarding alignment and roadway geometrics. Use of
2499-399: A path to the worker or other listeners. In the industrial or commercial setting, workers must comply with the appropriate Hearing conservation program . Administrative controls , such as the restriction of personnel in noisy areas, prevents unnecessary noise exposure. Personal protective equipment such as foam ear plugs or ear muffs to attenuate sound provide a last line of defense for
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#17328024751392618-411: A porous configuration of wood or metal. The effectiveness of post-construction acoustic treatment is limited by the amount of space able to be allocated to acoustic treatment, and so on-site acoustical wall panels are frequently made to conform to the shape of the preexisting space. This is done by "framing" the perimeter track into shape, infilling the acoustical substrate and then stretching and tucking
2737-457: A preamplifier and, therefore, do require phantom power, and circuits of modern passive ribbon microphones (i.e. those without the aforementioned preamplifier) are specifically designed to resist damage to the ribbon and transformer by phantom power. Also there are new ribbon materials available that are immune to wind blasts and phantom power. The carbon microphone was the earliest type of microphone. The carbon button microphone (or sometimes just
2856-414: A small battery. Power is necessary for establishing the capacitor plate voltage and is also needed to power the microphone electronics. Condenser microphones are also available with two diaphragms that can be electrically connected to provide a range of polar patterns , such as cardioid, omnidirectional, and figure-eight. It is also possible to vary the pattern continuously with some microphones, for example,
2975-409: A sound wave reflects off of a surface, and refers to both the sound energy transmitted through and dissipated by the surface material. Reverberation is the persistence of sound caused by repeated boundary reflections after the source of the sound stops. This principle is particularly important in enclosed spaces. Diffraction is the bending of sound waves around surfaces in the path of the wave. Refraction
3094-598: A static charge is embedded in an electret by the alignment of the static charges in the material, much the way a permanent magnet is made by aligning the magnetic domains in a piece of iron. Due to their good performance and ease of manufacture, hence low cost, the vast majority of microphones made today are electret microphones; a semiconductor manufacturer estimates annual production at over one billion units. They are used in many applications, from high-quality recording and lavalier (lapel mic) use to built-in microphones in small sound recording devices and telephones. Prior to
3213-478: A theatre, restaurant or railway station, enhancing the quality of music in a concert hall or recording studio, or suppressing noise to make offices and homes more productive and pleasant places to work and live. Architectural acoustic design is usually done by acoustic consultants. Bioacoustics concerns the scientific study of sound production and hearing in animals. It can include: acoustic communication and associated animal behavior and evolution of species; how sound
3332-432: A thin, usually corrugated metal ribbon suspended in a magnetic field. The ribbon is electrically connected to the microphone's output, and its vibration within the magnetic field generates the electrical signal. Ribbon microphones are similar to moving coil microphones in the sense that both produce sound by means of magnetic induction. Basic ribbon microphones detect sound in a bi-directional (also called figure-eight, as in
3451-587: A useful by-product of which is that RF condenser microphones can be operated in damp weather conditions that could create problems in DC-biased microphones with contaminated insulating surfaces. The Sennheiser MKH series of microphones use the RF biasing technique. A covert, remotely energized application of the same physical principle called the Thing was devised by Soviet Russian inventor Leon Theremin and used to bug
3570-424: A variable-resistance microphone/transmitter. Bell's liquid transmitter consisted of a metal cup filled with water with a small amount of sulfuric acid added. A sound wave caused the diaphragm to move, forcing a needle to move up and down in the water. The electrical resistance between the wire and the cup was then inversely proportional to the size of the water meniscus around the submerged needle. Elisha Gray filed
3689-476: A very limited frequency response range but are very robust devices. The Boudet microphone, which used relatively large carbon balls, was similar to the granule carbon button microphones. Unlike other microphone types, the carbon microphone can also be used as a type of amplifier, using a small amount of sound energy to control a larger amount of electrical energy. Carbon microphones found use as early telephone repeaters , making long-distance phone calls possible in
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3808-595: A very poor sound quality. The first microphone that enabled proper voice telephony was the (loose-contact) carbon microphone . This was independently developed by David Edward Hughes in England and Emile Berliner and Thomas Edison in the US. Although Edison was awarded the first patent in mid-1877 (after a long legal dispute), Hughes had demonstrated his working device in front of many witnesses some years earlier, and most historians credit him with its invention. The Berliner microphone found commercial success through
3927-413: A voltage when subjected to pressure—to convert vibrations into an electrical signal. An example of this is potassium sodium tartrate , which is a piezoelectric crystal that works as a transducer, both as a microphone and as a slimline loudspeaker component. Crystal microphones were once commonly supplied with vacuum tube (valve) equipment, such as domestic tape recorders. Their high output impedance matched
4046-553: Is a commonly used acoustical substrate, and commercial thermal insulations, such as those used in the insulation of boiler tanks, are frequently repurposed for noise-controlling acoustic use based on their effectiveness at minimizing reverberations. The ideal acoustical panels are those without a face or finish material that could interfere with the performance of the acoustical infill, but aesthetic and safety concerns typically lead to fabric coverings or other finishing materials to minimize impedance. Panel finishings are occasionally made of
4165-421: Is a function of frequency. The body of the microphone is not infinitely small and, as a consequence, it tends to get in its own way with respect to sounds arriving from the rear, causing a slight flattening of the polar response. This flattening increases as the diameter of the microphone (assuming it's cylindrical) reaches the wavelength of the frequency in question. Therefore, the smallest diameter microphone gives
4284-403: Is aimed at the surface of a window or other plane surface that is affected by sound. The vibrations of this surface change the angle at which the beam is reflected, and the motion of the laser spot from the returning beam is detected and converted to an audio signal. In a more robust and expensive implementation, the returned light is split and fed to an interferometer , which detects movement of
4403-528: Is also used to describe a set of electrokinetic effects that occur in heterogeneous liquids under influence of ultrasound. Environmental acoustics is concerned with the control of noise and vibrations caused by traffic, aircraft, industrial equipment, recreational activities and anything else that might be considered a nuisance. Acoustical engineers concerned with environmental acoustics face the challenge of measuring or predicting likely noise levels, determining an acceptable level for that noise, and determining how
4522-555: Is at least one practical application that exploits those weaknesses: the use of a medium-size woofer placed closely in front of a "kick drum" ( bass drum ) in a drum set to act as a microphone. A commercial product example is the Yamaha Subkick, a 6.5-inch (170 mm) woofer shock-mounted into a 10" drum shell used in front of kick drums. Since a relatively massive membrane is unable to transduce high frequencies while being capable of tolerating strong low-frequency transients,
4641-451: Is effective since the lowest sound emissions arise from vehicles moving smoothly at 30 to 60 kilometers per hour. Above that range, sound emissions double with every five miles per hour of speed. At the lowest speeds, braking and (engine) acceleration noise dominates. Selection of road surface pavement can make a difference of a factor of two in sound levels, for the speed regime above 30 kilometers per hour. Quieter pavements are porous with
4760-776: Is merely necessary to specify the best available quieting technology in selecting such building hardware. In other cases, shock mounting of systems to control vibration may be in order. In the case of plumbing systems, there are specific protocols developed, especially for water supply lines, to create isolation clamping of pipes within building walls. In the case of central air systems, it is important to baffle any ducts that could transmit sound between different building areas. Designing special-purpose rooms has more exotic challenges, since these rooms may have requirements for unusual features such as concert performance, sound studio recording , lecture halls. In these cases reverberation and reflection must be analyzed in order to not only quiet
4879-399: Is practically constant and the voltage across the capacitor changes instantaneously to reflect the change in capacitance. The voltage across the capacitor varies above and below the bias voltage. The voltage difference between the bias and the capacitor is seen across the series resistor. The voltage across the resistor is amplified for performance or recording. In most cases, the electronics in
Acoustical engineering - Misplaced Pages Continue
4998-625: Is present, a common office environment issue. If over-illumination is occurring, de-lamping or reduced light bank usage may apply. Photographers can quieten noisy still cameras on a film set using sound blimps . Reductions in cost of technology have allowed noise control technology to be used not only in performance facilities and recording studios, but also in noise-sensitive small businesses such as restaurants. Acoustically absorbent materials such as fiberglass duct liner, wood fiber panels and recycled denim jeans serve as artwork-bearing canvasses in environments in which aesthetics are important. Using
5117-571: Is produced by animals; the auditory mechanisms and neurophysiology of animals; the use of sound to monitor animal populations, and the effect of man-made noise on animals. This branch of acoustic engineering deals with the design of headphones, microphones , loudspeakers , sound systems, sound reproduction, and recording. There has been a rapid increase in the use of portable electronic devices which can reproduce sound and rely on electroacoustic engineering, e.g. mobile phones , portable media players , and tablet computers . The term "electroacoustics"
5236-531: Is the active addition of noise to reduce the annoyance of certain sounds, the opposite of soundproofing . Organizations each have their own standards, recommendations/guidelines, and directives for what levels of noise workers are permitted to be around before noise controls must be put into place. OSHA's requirements state that when workers are exposed to noise levels above 90 A-weighted decibels (dBA) in 8-hour time-weighted averages (TWA), administrative controls and/or new engineering controls must be implemented in
5355-429: Is the bending of sound waves caused by changes in the medium through which the wave is passing. For example, temperature gradients can cause sound wave refraction. Acoustical engineers apply these fundamental concepts, along with mathematical analysis, to control sound for a variety of applications. Noise control Noise control or noise mitigation is a set of strategies to reduce noise pollution or to reduce
5474-402: Is the best sound for a product, for instance, manipulating the sound of door closures on automobiles . Psychoacoustics tries to explain how humans respond to what they hear, whether that is an annoying noise or beautiful music. In many branches of acoustic engineering, a human listener is a final arbitrator as to whether a design is successful, for instance, whether sound localisation works in
5593-432: Is the electronic manipulation of audio signals using analog and digital signal processing . It is done for a variety of reasons, including: Audio engineers develop and use audio signal processing algorithms. Architectural acoustics (also known as building acoustics ) is the science and engineering of achieving a good sound within a building. Architectural acoustics can be about achieving good speech intelligibility in
5712-603: Is the most dramatic, there are many other work environments where sound levels may lie in the range of 70 to 75 decibels, entirely composed of office equipment, music, public address systems, and even exterior noise intrusion. Either type of environment may result in noise health effects if the sound intensity and exposure time is too great. In the case of industrial equipment, the most common techniques for noise protection of workers consist of shock mounting source equipment, creation of acrylic glass or other solid barriers, and provision of ear protection equipment . In certain cases
5831-436: Is the scientific study of sound in water. It is concerned with both natural and man-made sound and its generation underwater; how it propagates, and the perception of the sound by animals. Applications include sonar to locate submerged objects such as submarines , underwater communication by animals, observation of sea temperatures for climate change monitoring, and marine biology. Acoustic engineers working on vibration study
5950-756: Is the source, path, and receiver model by Bolt and Ingard. Hazardous noise can be controlled by reducing the noise output at its source, minimizing the noise as it travels along a path to the listener, and providing equipment to the listener or receiver to attenuate the noise. A variety of measures aim to reduce hazardous noise at its source. Programs such as Buy Quiet and the National Institute for Occupational Safety and Health (NIOSH) Prevention through design promote research and design of quiet equipment and renovation and replacement of older hazardous equipment with modern technologies. The principle of noise reduction through pathway modifications applies to
6069-441: Is to sounds arriving at different angles about its central axis. The polar patterns illustrated above represent the locus of points in polar coordinates that produce the same signal level output in the microphone if a given sound pressure level (SPL) is generated from that point. How the physical body of the microphone is oriented relative to the diagrams depends on the microphone design. For large-membrane microphones such as in
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#17328024751396188-548: The MAX Light Rail system in Portland, Oregon (1983). Noise barriers can be applied to existing or planned surface transportation projects. They are one of the most effective actions taken in retrofitting existing roadways and commonly can reduce adjacent land-use sound levels by up to ten decibels. A computer model is required to design the barrier since terrain, micrometeorology and other locale-specific factors make
6307-477: The Røde NT2000 or CAD M179. There are two main categories of condenser microphones, depending on the method of extracting the audio signal from the transducer: DC-biased microphones, and radio frequency (RF) or high frequency (HF) condenser microphones. With a DC-biased condenser microphone , the plates are biased with a fixed charge ( Q ). The voltage maintained across the capacitor plates changes with
6426-405: The diagram below) pattern because the ribbon is open on both sides. Also, because the ribbon has much less mass it responds to the air velocity rather than the sound pressure . Though the symmetrical front and rear pickup can be a nuisance in normal stereo recording, the high side rejection can be used to advantage by positioning a ribbon microphone horizontally, for example above cymbals, so that
6545-406: The 2010s, there has been increased interest and research into making piezoelectric MEMS microphones which are a significant architectural and material change from existing condenser style MEMS designs. In a plasma microphone, a plasma arc of ionized gas is used. The sound waves cause variations in the pressure around the plasma in turn causing variations in temperature which alter the conductance of
6664-940: The 20th century was only commonly the practice of music-listening enthusiasts. However, developments in home recording technology and fidelity have led to a drastic increase in the spread and popularity of residential acoustic treatment in the pursuit of home recording fidelity and accuracy. A large secondary market of homemade and home use acoustic panels, bass trap, and similar constructed products has developed resulting from this demand, with many small companies and individuals wrapping industrial and commercial-grade insulations in fabric for use in home recording studios, theatre rooms, and music practice spaces. Communities may use zoning codes to isolate noisy urban activities from areas that should be protected from such unhealthy exposures and to establish noise standards in areas that may not be conducive to such isolation strategies. Because low-income neighborhoods are often at greater risk of noise pollution,
6783-519: The DoD's requirements. The European Parliament and Council directive require noise levels to be reduced or eliminated using administrative and engineering controls. This directive requires lower exposure action levels of 80 dBA for 8 hours with 135 dB peak SPL, along with upper exposure action levels of 85 dBA for 8 hours with 137 peak dBSPL. Exposure limits are 87 dBA for 8 hours with peak levels of 140 peak dBSPL. An effective model for noise control
6902-463: The English physicist Robert Hooke was the first to experiment with a medium other than air with the invention of the " lovers' telephone " made of stretched wire with a cup attached at each end. In 1856, Italian inventor Antonio Meucci developed a dynamic microphone based on the generation of electric current by moving a coil of wire to various depths in a magnetic field. This method of modulation
7021-515: The Oktava (pictured above), the upward direction in the polar diagram is usually perpendicular to the microphone body, commonly known as "side fire" or "side address". For small diaphragm microphones such as the Shure (also pictured above), it usually extends from the axis of the microphone commonly known as "end fire" or "top/end address". Some microphone designs combine several principles in creating
7140-574: The PACS ( Physics and Astronomy Classification Scheme ) coding used by the Acoustical Society of America . Aeroacoustics is concerned with how noise is generated by the movement of air, for instance via turbulence, and how sound propagates through the fluid air. Aeroacoustics plays an important role in understanding how noise is generated by aircraft and wind turbines , as well as exploring how wind instruments work. Audio signal processing
7259-608: The US Ambassador's residence in Moscow between 1945 and 1952. An electret microphone is a type of condenser microphone invented by Gerhard Sessler and Jim West at Bell laboratories in 1962. The externally applied charge used for a conventional condenser microphone is replaced by a permanent charge in an electret material. An electret is a ferroelectric material that has been permanently electrically charged or polarized . The name comes from electrostatic and magnet ;
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#17328024751397378-506: The acoustical scientist to arrive at the best cost-effective means of creating a quiet interior (normally 45 dBA ). The most important elements of design of the building skin are usually: glazing (glass thickness, double pane design etc.), perforated metal (used internally or externally), roof material, caulking standards, chimney baffles, exterior door design, mail slots, attic ventilation ports, and mounting of through-the-wall air conditioners. Regarding sound generated inside
7497-414: The air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone , which uses a coil of wire suspended in a magnetic field; the condenser microphone , which uses the vibrating diaphragm as a capacitor plate; and the contact microphone , which uses a crystal of piezoelectric material. Microphones typically need to be connected to a preamplifier before
7616-511: The alteration of direct and indirect pathways for noise. Noise that travels across reflective surfaces, such as smooth floors, can be hazardous. Pathway alterations include physical materials, such as foam, absorb sound and walls to provide a sound barrier that modifies existing systems that decrease hazardous noise. Sound dampening enclosures for loud equipment and isolation chambers from which workers can remotely control equipment can also be designed. These methods prevent sound from traveling along
7735-619: The best high fidelity conventional microphones. Fiber-optic microphones do not react to or influence any electrical, magnetic, electrostatic or radioactive fields (this is called EMI/RFI immunity). The fiber-optic microphone design is therefore ideal for use in areas where conventional microphones are ineffective or dangerous, such as inside industrial turbines or in magnetic resonance imaging (MRI) equipment environments. Fiber-optic microphones are robust, resistant to environmental changes in heat and moisture, and can be produced for any directionality or impedance matching . The distance between
7854-472: The best omnidirectional characteristics at high frequencies. The wavelength of sound at 10 kHz is 1.4" (3.5 cm). The smallest measuring microphones are often 1/4" (6 mm) in diameter, which practically eliminates directionality even up to the highest frequencies. Omnidirectional microphones, unlike cardioids, do not employ resonant cavities as delays, and so can be considered the "purest" microphones in terms of low coloration; they add very little to
7973-600: The building itself. The most common perception of IIC noise is from the footfall of occupants in living spaces above. Low-frequency noise is transferred easily through the ground and buildings. This type of noise is more difficult to abate, but consideration must be given to isolating the floor assembly above or hanging the lower ceiling on resilient channel . Both of the transmission effects noted above may emanate either from building occupants or from building mechanical systems such as elevators, plumbing systems or heating, ventilating and air conditioning units. In some cases, it
8092-727: The building, there are two principal types of transmission. Firstly, airborne sound travels through walls or floor and ceiling assemblies and can emanate from either human activities in adjacent living spaces or from mechanical noise within the building systems. Human activities might include voice, noise from amplified sound systems, or animal noise. Mechanical systems are elevator systems, boilers , refrigeration or air conditioning systems, generators and trash compactors. Aerodynamic sources include fans, pneumatics, and combustion. Noise control for aerodynamic sources include quiet air nozzles , pneumatic silencers and quiet fan technology . Since many mechanical sounds are inherently loud,
8211-407: The capsule (around 5 to 100 pF ) and the value of the bias resistor (100 MΩ to tens of GΩ) form a filter that is high-pass for the audio signal, and low-pass for the bias voltage. Note that the time constant of an RC circuit equals the product of the resistance and capacitance. Within the time frame of the capacitance change (as much as 50 ms at 20 Hz audio signal), the charge
8330-465: The case of construction of new (or remodeled) apartments , condominiums , hospitals , and hotels , many states and cities have stringent building codes with requirements of acoustical analysis, in order to protect building occupants. With regard to exterior noise, the codes usually require measurement of the exterior acoustic environment in order to determine the performance standard required for exterior building skin design. The architect can work with
8449-560: The case of more conventional office environments, the techniques in architectural acoustics discussed above may apply. Other solutions may involve researching the quietest models of office equipment, particularly printers and photocopy machines. Impact printers and other equipment were often fitted with "acoustic hoods", enclosures to reduce emitted noise. One source of annoying, if not loud, sound level emissions are lighting fixtures (notably older fluorescent globes). These fixtures can be retrofitted or analyzed to see whether over-illumination
8568-487: The design of noise barriers, sound absorbers, suppressors, and buffer zones, and the use of hearing protection ( earmuffs or earplugs ). Besides noise control, acoustical engineering also covers positive uses of sound, such as the use of ultrasound in medicine , programming digital synthesizers , designing concert halls to enhance the sound of orchestras and specifying railway station sound systems so that announcements are intelligible . Acoustic engineers usually possess
8687-425: The desired polar pattern. This ranges from shielding (meaning diffraction/dissipation/absorption) by the housing itself to electronically combining dual membranes. An omnidirectional (or nondirectional) microphone's response is generally considered to be a perfect sphere in three dimensions. In the real world, this is not the case. As with directional microphones, the polar pattern for an "omnidirectional" microphone
8806-490: The distance between the plates. Because the capacitance of the plates is inversely proportional to the distance between them, the vibrations produce changes in capacitance. These changes in capacitance are used to measure the audio signal . The assembly of fixed and movable plates is called an element or capsule . Condenser microphones span the range from telephone mouthpieces through inexpensive karaoke microphones to high-fidelity recording microphones. They generally produce
8925-486: The effective dynamic range of ribbon microphones at low frequencies. Protective wind screens can reduce the danger of damaging a vintage ribbon, and also reduce plosive artifacts in the recording. Properly designed wind screens produce negligible treble attenuation. In common with other classes of dynamic microphone, ribbon microphones do not require phantom power; in fact, this voltage can damage some older ribbon microphones. Some new modern ribbon microphone designs incorporate
9044-656: The endeavor a very complex undertaking. For example, a roadway in cut or strong prevailing winds can produce a setting where atmospheric sound propagation is unfavorable to any noise barrier. As in the case of roadway noise, little progress has been made in quelling aircraft noise at the source, other than elimination of loud engine designs from the 1960s and earlier. Because of its velocity and volume, jet turbine engine exhaust noise defies reduction by any simple means. The most promising forms of aircraft noise abatement are through land planning, flight operations restrictions and residential soundproofing . Flight restrictions can take
9163-466: The era before vacuum tubes. Called a Brown's relay, these repeaters worked by mechanically coupling a magnetic telephone receiver to a carbon microphone: the faint signal from the receiver was transferred to the microphone, where it modulated a stronger electric current, producing a stronger electrical signal to send down the line. A crystal microphone or piezo microphone uses the phenomenon of piezoelectricity —the ability of some materials to produce
9282-453: The establishment of such zoning codes is often an environmental justice issue. Mixed-use areas present especially difficult conflicts that require special attention to the need to protect people from the harmful effects of noise pollution. Noise is generally one consideration in an environmental impact statement , if applicable (such as transportation system construction). General: Microphone A microphone , colloquially called
9401-526: The fabric into the perimeter frame system. On-site wall panels can be constructed to work around door frames, baseboard, or any other intrusion. Large panels (generally greater than 50 feet) can be created on walls and ceilings with this method. Double-glazed and thicker windows can also prevent sound transmission from the outdoors. Industrial noise is traditionally associated with manufacturing settings where industrial machinery produces intense sound levels, often upwards of 85 decibels. While this circumstance
9520-515: The form of preferred runway use, departure flight path and slope, and time-of-day restrictions. These tactics are sometimes controversial since they can impact aircraft safety, flying convenience and airline economics. In 1979, the US Congress authorized the FAA to devise technology and programs to attempt to insulate homes near airports. While this obviously does not aid the exterior environment,
9639-459: The function and design of musical instruments including electronic synthesizers ; the human voice (the physics and neurophysiology of singing ); computer analysis of music and composition; the clinical use of music in music therapy, and the perception and cognition of music . Noise control is a set of strategies to reduce noise pollution by reducing noise at its source, by inhibiting sound propagation using noise barriers or similar, or by
9758-413: The granules, causing the contact area between each pair of adjacent granules to change, and this causes the electrical resistance of the mass of granules to change. The changes in resistance cause a corresponding change in the current flowing through the microphone, producing the electrical signal. Carbon microphones were once commonly used in telephones; they have extremely low-quality sound reproduction and
9877-636: The health of populations residing in or occupying areas, both indoor and outdoor, near entertainment venues that feature amplified sounds and music that present significant challenges for effective noise mitigation strategies. Multiple techniques have been developed to address interior sound levels, many of which are encouraged by local building codes . In the best case of project designs, planners are encouraged to work with design engineers to examine trade-offs of roadway design and architectural design. These techniques include design of exterior walls, party walls, and floor and ceiling assemblies; moreover, there are
9996-770: The high input impedance (typically about 10 MΩ) of the vacuum tube input stage well. They were difficult to match to early transistor equipment and were quickly supplanted by dynamic microphones for a time, and later small electret condenser devices. The high impedance of the crystal microphone made it very susceptible to handling noise, both from the microphone itself and from the connecting cable. Piezoelectric transducers are often used as contact microphones to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging environments, such as underwater under high pressure. Saddle-mounted pickups on acoustic guitars are generally piezoelectric devices that contact
10115-403: The impact of that noise, whether outdoors or indoors. The main areas of noise mitigation or abatement are: transportation noise control, architectural design, urban planning through zoning codes , and occupational noise control. Roadway noise and aircraft noise are the most pervasive sources of environmental noise. Social activities may generate noise levels that consistently affect
10234-513: The internal baffle, allowing the selection of several response patterns ranging from "figure-eight" to "unidirectional". Such older ribbon microphones, some of which still provide high-quality sound reproduction, were once valued for this reason, but a good low-frequency response could be obtained only when the ribbon was suspended very loosely, which made them relatively fragile. Modern ribbon materials, including new nanomaterials , have now been introduced that eliminate those concerns and even improve
10353-407: The listener. Studies on noise barriers have shown mixed results on their ability to effectively reduce noise pollution . Electric and hybrid vehicles could reduce noise pollution, but only if those vehicles make up a high proportion of total vehicles on the road; even if traffic in an urban area reached a makeup of fifty percent electric vehicles, the overall noise reduction achieved would only be
10472-561: The machine processing of speech. Ensuring speech is transmitted intelligibly , efficiently and with high quality; in rooms, through public address systems and through telephone systems are other important areas of study. Ultrasonics deals with sound waves in solids, liquids and gases at frequencies too high to be heard by the average person. Specialist areas include medical ultrasonics (including medical ultrasonography ), sonochemistry , nondestructive testing , material characterisation and underwater acoustics ( sonar ). Underwater acoustics
10591-410: The machinery itself can be re-designed to operate in a manner less prone to produce grating, grinding, frictional, or other motions that induce sound emissions. In recent years, Buy Quiet programs and initiatives have arisen in an effort to combat occupational noise exposures. These programs promote the purchase of quieter tools and equipment and encourage manufacturers to design quieter equipment. In
10710-423: The microphone itself contribute no voltage gain as the voltage differential is quite significant, up to several volts for high sound levels. RF condenser microphones use a comparatively low RF voltage, generated by a low-noise oscillator. The signal from the oscillator may either be amplitude modulated by the capacitance changes produced by the sound waves moving the capsule diaphragm, or the capsule may be part of
10829-489: The microphone's light source and its photodetector may be up to several kilometers without need for any preamplifier or another electrical device, making fiber-optic microphones suitable for industrial and surveillance acoustic monitoring. Fiber-optic microphones are used in very specific application areas such as for infrasound monitoring and noise cancellation . They have proven especially useful in medical applications, such as allowing radiologists, staff and patients within
10948-407: The motions and interactions of mechanical systems with their environments, including measurement, analysis and control. This might include: ground vibrations from railways and construction; vibration isolation to reduce noise getting into recording studios; studying the effects of vibration on humans ( vibration white finger ); vibration control to protect a bridge from earthquakes , or modelling
11067-511: The next breakthrough with the first condenser microphone . In 1923, the first practical moving coil microphone was built. The Marconi-Sykes magnetophone, developed by Captain H. J. Round , became the standard for BBC studios in London. This was improved in 1930 by Alan Blumlein and Herbert Holman who released the HB1A and was the best standard of the day. Also in 1923, the ribbon microphone
11186-461: The noise can be controlled. Environmental acoustics work is usually done by acoustic consultants or those working in environmental health . Recent research work has put a strong emphasis on soundscapes , the positive use of sound (e.g. fountains, bird song), and the preservation of tranquility . Musical acoustics is concerned with researching and describing the physics of music and its perception – how sounds employed as music work. This includes:
11305-495: The plasma. These variations in conductance can be picked up as variations superimposed on the electrical supply to the plasma. This is an experimental form of microphone. A loudspeaker, a transducer that turns an electrical signal into sound waves, is the functional opposite of a microphone. Since a conventional speaker is similar in construction to a dynamic microphone (with a diaphragm, coil and magnet), speakers can actually work "in reverse" as microphones. Reciprocity applies, so
11424-471: The powerful and noisy magnetic field to converse normally, inside the MRI suites as well as in remote control rooms. Other uses include industrial equipment monitoring and audio calibration and measurement, high-fidelity recording and law enforcement. Laser microphones are often portrayed in movies as spy gadgets because they can be used to pick up sound at a distance from the microphone equipment. A laser beam
11543-428: The principal design element is to require the wall or ceiling assembly to meet certain performance standards, (typically Sound transmission class of 50), which allows considerable attenuation of the sound level reaching occupants. The second type of interior sound is called Impact Insulation Class (IIC) transmission. This effect arises not from airborne transmission , but rather from the transmission of sound through
11662-415: The principal sound input to the principal axis (end- or side-address) of the microphone are used to describe the microphone. The condenser microphone , invented at Western Electric in 1916 by E. C. Wente, is also called a capacitor microphone or electrostatic microphone —capacitors were historically called condensers. The diaphragm acts as one plate of a capacitor, and audio vibrations produce changes in
11781-836: The program has been effective for residential and school interiors. Some of the airports at which the technology was applied early on were San Francisco International Airport , Seattle-Tacoma International Airport , John Wayne International Airport and San Jose International Airport in California. The underlying technology is a computer model which simulates the propagation of aircraft noise and its penetration into buildings. Variations in aircraft types, flight patterns and local meteorology can be analyzed along with benefits of alternative building retrofit strategies such as roof upgrading, window glazing improvement, fireplace baffling, caulking construction seams and other measures. The computer model allows cost-effectiveness evaluations of
11900-474: The proliferation of MEMS microphones, nearly all cell-phone, computer, PDA and headset microphones were electret types. Unlike other capacitor microphones, they require no polarizing voltage, but often contain an integrated preamplifier that does require power. This preamplifier is frequently phantom powered in sound reinforcement and studio applications. Monophonic microphones designed for personal computers (PCs), sometimes called multimedia microphones, use
12019-406: The propagation of structure-borne sound through buildings. Although the way in which sound interacts with its surroundings is often extremely complex, there are a few ideal sound wave behaviours that are fundamental to understanding acoustical design. Complex sound wave behaviors include absorption , reverberation , diffraction , and refraction . Absorption is the loss of energy that occurs when
12138-451: The rear lobe picks up sound only from the cymbals. Crossed figure 8, or Blumlein pair , stereo recording is gaining in popularity, and the figure-eight response of a ribbon microphone is ideal for that application. Other directional patterns are produced by enclosing one side of the ribbon in an acoustic trap or baffle, allowing sound to reach only one side. The classic RCA Type 77-DX microphone has several externally adjustable positions of
12257-461: The resulting microphone has the same impairments as a single-driver loudspeaker: limited low- and high-end frequency response, poorly controlled directivity , and low sensitivity . In practical use, speakers are sometimes used as microphones in applications where high bandwidth and sensitivity are not needed such as intercoms , walkie-talkies or video game voice chat peripherals, or when conventional microphones are in short supply. However, there
12376-540: The rooms, but to prevent echo effects from occurring. In these situations special sound baffles and sound absorptive lining materials may be specified to dampen unwanted effects. Acoustical wall and ceiling panels are a common commercial and residential solution for noise control in already-constructed buildings. Acoustic panels may be constructed of a variety of materials, though commercial acoustic applications will frequently be composed of fiberglass or mineral wool-based acoustic substrates. For example, Mineral fiberboard
12495-498: The same CMOS chip making the chip a digital microphone and so more readily integrated with modern digital products. Major manufacturers producing MEMS silicon microphones are Wolfson Microelectronics (WM7xxx) now Cirrus Logic, InvenSense (product line sold by Analog Devices ), Akustica (AKU200x), Infineon (SMM310 product), Knowles Electronics, Memstech (MSMx), NXP Semiconductors (division bought by Knowles ), Sonion MEMS, Vesper, AAC Acoustic Technologies, and Omron. More recently, since
12614-436: The same dynamic principle as in a loudspeaker , only reversed. A small movable induction coil , positioned in the magnetic field of a permanent magnet, is attached to the diaphragm. When sound enters through the windscreen of the microphone, the sound wave moves the diaphragm which moves the coil in the magnetic field, producing a varying voltage across the coil through electromagnetic induction. Ribbon microphones use
12733-538: The side because sound arriving at the front and back at the same time creates no gradient between the two. The characteristic directional pattern of a pure pressure-gradient microphone is like a figure-8. Other polar patterns are derived by creating a capsule that combines these two effects in different ways. The cardioid, for instance, features a partially closed backside, so its response is a combination of pressure and pressure-gradient characteristics. A microphone's directionality or polar pattern indicates how sensitive it
12852-403: The signal can be recorded or reproduced . In order to speak to larger groups of people, a need arose to increase the volume of the human voice. The earliest devices used to achieve this were acoustic megaphones. Some of the first examples, from fifth-century-BC Greece, were theater masks with horn-shaped mouth openings that acoustically amplified the voice of actors in amphitheaters . In 1665,
12971-438: The speaker is often ideal for picking up the kick drum while reducing bleed from the nearby cymbals and snare drums. The inner elements of a microphone are the primary source of differences in directivity. A pressure microphone uses a diaphragm between a fixed internal volume of air and the environment and responds uniformly to pressure from all directions, so it is said to be omnidirectional. A pressure-gradient microphone uses
13090-479: The strings passing over the saddle. This type of microphone is different from magnetic coil pickups commonly visible on typical electric guitars , which use magnetic induction, rather than mechanical coupling, to pick up vibration. A fiber-optic microphone converts acoustic waves into electrical signals by sensing changes in light intensity, instead of sensing changes in capacitance or magnetic fields as with conventional microphones. During operation, light from
13209-423: The surface by changes in the optical path length of the reflected beam. The former implementation is a tabletop experiment; the latter requires an extremely stable laser and precise optics. A new type of laser microphone is a device that uses a laser beam and smoke or vapor to detect sound vibrations in free air. On August 25, 2009, U.S. patent 7,580,533 issued for a Particulate Flow Detection Microphone based on
13328-563: The use by Alexander Graham Bell for his telephone and Berliner became employed by Bell. The carbon microphone was critical in the development of telephony, broadcasting and the recording industries. Thomas Edison refined the carbon microphone into his carbon-button transmitter of 1886. This microphone was employed at the first radio broadcast ever, a performance at the New York Metropolitan Opera House in 1910. In 1916, E.C. Wente of Western Electric developed
13447-438: The use of ear protection ( earmuffs or earplugs ). Control at the source is the most cost-effective way of providing noise control. Noise control engineering applied to cars and trucks is known as noise, vibration, and harshness (NVH). Other techniques to reduce product noise include vibration isolation , application of acoustic absorbent and acoustic enclosures. Acoustical engineering can go beyond noise control to look at what
13566-403: The vibrations in the air, according to the capacitance equation (C = Q ⁄ V ), where Q = charge in coulombs , C = capacitance in farads and V = potential difference in volts . A nearly constant charge is maintained on the capacitor. As the capacitance changes, the charge across the capacitor does change very slightly, but at audible frequencies it is sensibly constant. The capacitance of
13685-462: The word." In 1861, German inventor Johann Philipp Reis built an early sound transmitter (the " Reis telephone ") that used a metallic strip attached to a vibrating membrane that would produce intermittent current. Better results were achieved in 1876 with the " liquid transmitter " design in early telephones from Alexander Graham Bell and Elisha Gray – the diaphragm was attached to a conductive rod in an acid solution. These systems, however, gave
13804-1178: The workplace. OSHA also requires that impulse noises and impact noises must be controlled to prevent these noises reaching past 140 dB peak sound pressure levels (SPL). MSHA requires that administrative and/or engineering controls must be implemented in the workplace when miners are exposed to levels above 90 dBA TWA. If noise levels exceed 115 dBA, miners are required to wear hearing protection. MSHA, therefore, requires that noise levels be reduced below 115 dB TWA. Measuring noise levels for noise control decision making must integrate all noises from 90 dBA to 140 dBA. The FRA recommends that worker exposure to noise should be reduced when their noise exposure exceeds 90 dBA for an 8-hour TWA. Noise measurements must integrate all noises, including intermittent, continuous, impact, and impulse noises of 80 dBA to 140 dBA. The Department of Defense (DoD) suggests that noise levels be controlled primarily through engineering controls. The DoD requires that all steady-state noises be reduced to levels below 85 dBA and that impulse noises be reduced below 140 dB peak SPL. TWA exposures are not considered for
13923-652: Was a demand for high-fidelity microphones and greater directionality. Electro-Voice responded with their Academy Award -winning shotgun microphone in 1963. During the second half of the 20th century, development advanced quickly with the Shure Brothers bringing out the SM58 and SM57 . Microphones are categorized by their transducer principle (condenser, dynamic, etc.) and by their directional characteristics (omni, cardioid, etc.). Sometimes other characteristics such as diaphragm size, intended use or orientation of
14042-428: Was also the most enduring method for the technology of the telephone as well. Speaking of his device, Meucci wrote in 1857, "It consists of a vibrating diaphragm and an electrified magnet with a spiral wire that wraps around it. The vibrating diaphragm alters the current of the magnet. These alterations of current, transmitted to the other end of the wire, create analogous vibrations of the receiving diaphragm and reproduce
14161-399: Was introduced, another electromagnetic type, believed to have been developed by Harry F. Olson , who applied the concept used in a ribbon speaker to making a microphone. Over the years these microphones were developed by several companies, most notably RCA that made large advancements in pattern control, to give the microphone directionality. With television and film technology booming there
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