Acoustical engineering

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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.

Contents

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. [1] Noise control principles are implemented into technology and design in a variety of ways, including control by redesigning sound sources, the design of noise barriers, sound absorbers, suppressors, and buffer zones, and the use of hearing protection (earmuffs or earplugs).

The transparent baffles inside this auditorium were installed to optimise sound projection and reproduction, key factors in acoustical engineering. Hamer Hall equipment detail.jpg
The transparent baffles inside this auditorium were installed to optimise sound projection and reproduction, key factors in acoustical engineering.

But acoustical engineering is not just about noise control; it also covers positive uses of sound, from the use of ultrasound in medicine to the programming of digital sound synthesizers, and from designing a concert hall to enhance the sound of an orchestra [2] to specifying a railway station's sound system so announcements are intelligible. [3]

Acoustic engineer (professional)

Acoustic engineers usually possess a bachelor's degree or higher qualification in acoustics, [4] 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. [5] 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. [6] [7] Acousticians are also involved in researching and understanding sound scientifically. Some positions, such as faculty require 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).

Subdisciplines

The listed subdisciplines are loosely based on the PACS (Physics and Astronomy Classification Scheme) coding used by the Acoustical Society of America. [8]

Aeroacoustics

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 musical instruments work. [9]

Audio signal processing

Audio signal processing is the electronic manipulation of audio signals using analog and digital signal processing.

Audio signal processing is done for a variety of reasons such as:

Audio engineers develop and use audio signal processing algorithms.

Architectural acoustics

Disney's Concert Hall was meticulously designed for superior acoustical qualities. Disney Concert Hall by Carol Highsmith.jpg
Disney's Concert Hall was meticulously designed for superior acoustical qualities.
Ceiling of Culture Palace (Tel Aviv) concert hall is covered with perforated metal panels Heichal Hatarbut1.jpg
Ceiling of Culture Palace (Tel Aviv) concert hall is covered with perforated metal panels

Architectural acoustics (also known as building acoustics) is the science and engineering of achieving a good sound within a building. [11] Architectural acoustics can be about achieving good speech intelligibility in 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. [12] Architectural acoustic design is usually done by acoustic consultants. [13]

Bioacoustics

Bioacoustics usually concerns the scientific study of sound production and hearing in animals. It can include: acoustic communication and associated animal behaviour and evolution of species; how sound 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. [14]

Electroacoustics

This branch of acoustic engineering deals with the design of headphones, microphones, loudspeakers, sound systems, sound reproduction and recording. [15] 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.

This term is also used for a set of electrokinetic effects that occur in heterogeneous liquids under influence of ultrasound. [16] There is International Standard that describes such electroacoustic effects in details. [17]

Environmental noise

At outdoor concerts like Woodstock, acoustic analysis is critical to creating the best experience for the audience and the performers. Woodstock 2007.jpg
At outdoor concerts like Woodstock, acoustic analysis is critical to creating the best experience for the audience and the performers.

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. [1] 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 the noise can be controlled. Environmental acoustics work is usually done by acoustic consultants or those working in environmental health. [13] 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. [18]

Musical acoustics

Musical acoustics is concerned with researching and describing the physics of music and its perception – how sounds employed as music work. This includes: 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. [19]

Noise control

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 the use of ear protection (earmuffs or earplugs). [20] 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 is the best sound for a product, [21] for instance, manipulating the sound of door closures on automobiles.

Psychoacoustics

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 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." [10]

Speech

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 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. [22]

Ultrasonics

Ultrasound image of a fetus in the womb, viewed at 12 weeks of pregnancy (bidimensional-scan) CRL Crown rump length 12 weeks ecografia Dr. Wolfgang Moroder.jpg
Ultrasound image of a fetus in the womb, viewed at 12 weeks of pregnancy (bidimensional-scan)

Ultrasonics deals with sound waves in solids, liquids and gases at frequencies too high to be heard by the average person. Specialists areas include medical ultrasonics (including medical ultrasonography), sonochemistry, nondestructive testing, material characterisation and underwater acoustics (sonar). [23]

Underwater acoustics

Underwater acoustics 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. [24]

Vibration and dynamics

Acoustic engineers working on vibration study 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 the propagation of structure-borne sound through buildings. [25]

Fundamental science

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 a sound wave reflects off of a surface. Just as light waves reflect off of surfaces, sound waves also reflect off of surfaces, and every reflection results in a loss of energy. Absorption refers both to the sound that transmits through and the energy that is dissipated by a material. [26] Reverberation is the persistence of sound that is caused by repeated boundary reflections after the source of the sound stops. This principle is particularly important in enclosed spaces. In addition to reflecting off of surfaces, sound waves also bend around surfaces in the path of the waves. This bending is known as diffraction. Refraction is another kind of sound wave bending. This type of bending, however, is caused by changes in the medium through which the wave is passing and not the presence of obstacles in the path of a sound wave. Temperature gradients, for example, cause bending in sound waves. [27] Acoustical engineers apply these fundamental concepts, along with complex mathematical analysis, to control sound for a variety of applications.

Associations

See also

Related Research Articles

Acoustics Branch of physics involving mechanical waves

Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Audio signal processing is a subfield of signal processing that is concerned with the electronic manipulation of audio signals. Audio signals are electronic representations of sound waves—longitudinal waves which travel through air, consisting of compressions and rarefactions. The energy contained in audio signals is typically measured in decibels. As audio signals may be represented in either digital or analog format, processing may occur in either domain. Analog processors operate directly on the electrical signal, while digital processors operate mathematically on its digital representation.

Noise An unwanted sound

Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, noise is indistinguishable from desired sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound.

Room acoustics describes how sound behaves in an enclosed space. Sound of different frequencies behaves differently in a room. Reflections between walls, floor and ceiling create room modes at specific frequencies and locations. Reflections also produce reverberation.

Bioacoustics

Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion and reception in animals. This involves neurophysiological and anatomical basis of sound production and detection, and relation of acoustic signals to the medium they disperse through. The findings provide clues about the evolution of acoustic mechanisms, and from that, the evolution of animals that employ them.

Sound reinforcement system

A sound reinforcement system is the combination of microphones, signal processors, amplifiers, and loudspeakers in enclosures all controlled by a mixing console that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience. In many situations, a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage, typically by using electronic effects, such as reverb, as opposed to simply amplifying the sources unaltered.

Architectural acoustics Science and engineering of achieving a good sound within a building

Architectural acoustics is the science and engineering of achieving a good sound within a building and is a branch of acoustical engineering. The first application of modern scientific methods to architectural acoustics was carried out by the American physicist Wallace Sabine in the Fogg Museum lecture room. He applied his new found knowledge to the design of Symphony Hall, Boston.

Acoustical Society of America

The Acoustical Society of America (ASA) is an international scientific society founded in 1929 dedicated to generating, disseminating and promoting the knowledge of acoustics and its practical applications. The Society is primarily a voluntary organization of about 7500 members and attracts the interest, commitment, and service of many professionals.

Whitlow W. L. Au was a leading expert in bioacoustics specializing in biosonar of odontocetes. He is author of the widely known book The Sonar of Dolphins (1993) and, with Mardi Hastings, Principles of Marine Bioacoustics (2008). Au was honored as a Fellow of the Acoustical Society of America in 1990 and awarded the ASA's first Silver Medal in Animal Bioacoustics in 1998. He was graduate advisor to MacArthur Fellow Kelly Benoit-Bird, who credits Au for discovering how sophisticated dolphin sonar is, developing dolphin-inspired machine sonars to separate different species of fish with the goal of protecting sensitive species, and for making numerous contributions to the description of Humpback whale song, which helped protect these whales from ship noise and ship traffic.

John Ffowcs Williams British engineer-scientist

John "Shôn" Eirwyn Ffowcs Williams was Emeritus Rank Professor of Engineering at the University of Cambridge and a former Master of Emmanuel College, Cambridge (1996–2002). He may be best known for his contributions to Aeroacoustics, in particular for his work on Concorde. Together with one of his students, David Hawkings, he introduced the far-field integration method in computational aeroacoustics based on Lighthill's acoustic analogy, known as the Ffowcs Williams-Hawkings analogy.

Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, harshness is a subjective quality, and is measured either via "jury" evaluations, or with analytical tools that can provide results reflecting human subjective impressions. These latter tools belong to the field known as "psychoacoustics."

Underwater acoustics The study of the propagation of sound in water and the interaction of sound waves with the water and its boundaries

Underwater acoustics is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries. The water may be in the ocean, a lake, a river or a tank. Typical frequencies associated with underwater acoustics are between 10 Hz and 1 MHz. The propagation of sound in the ocean at frequencies lower than 10 Hz is usually not possible without penetrating deep into the seabed, whereas frequencies above 1 MHz are rarely used because they are absorbed very quickly. Underwater acoustics is sometimes known as hydroacoustics.

The ASA Silver Medal is an award presented by the Acoustical Society of America to individuals, without age limitation, for contributions to the advancement of science, engineering, or human welfare through the application of acoustic principles or through research accomplishments in acoustics. The medal is awarded in a number of categories depending on the technical committee responsible for making the nomination.

Acoustic quieting is the process of making machinery quieter by damping vibrations to prevent them from reaching the observer. Machinery vibrates, causing sound waves in air, hydroacoustic waves in water, and mechanical stresses in solid matter. Quieting is achieved by absorbing the vibrational energy or minimizing the source of the vibration. It may also be redirected away from the observer.

The following outline is provided as an overview of and topical guide to acoustics:

Sound Vibration that propagates as an acoustic wave

In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.

Audio engineer Engineer involved in the recording, reproduction, or reinforcement of sound

An audio engineer helps to produce a recording or a live performance, balancing and adjusting sound sources using equalization, dynamics processing and audio effects, mixing, reproduction, and reinforcement of sound. Audio engineers work on the "technical aspect of recording—the placing of microphones, pre-amp knobs, the setting of levels. The physical recording of any project is done by an engineer ... the nuts and bolts."

An autonomous recording unit (ARU) is a self-contained audio recording device that is deployed in marine or terrestrial environments for bioacoustical monitoring. The unit is used in both marine and terrestrial environments to track the behavior of animals and monitor their ecosystems. On a terrestrial level, the ARU can detect noises coming from bird habitats and determine relative emotions that each bird conveys along with the population of the birds and the relative vulnerability of the ecosystem. The ARU can also be used to understand noises made by marine life to see how the animals' communication affects the operation of their ecosystem. When underwater, the ARU can track the sound that human made machines make and see the effect those sounds have on marine life ecosystems. Up to 44 work days can be saved through the utilization of ARU's, along with their ability to discover more species.

ACTRAN is a finite element-based computer aided engineering software modeling the acoustic behavior of mechanical systems and parts. Actran is being developed by Free Field Technologies, a Belgian software company founded in 1998 by Jean-Pierre Coyette and Jean-Louis Migeot. Free Field Technologies is a wholly owned subsidiary of the MSC Software Corporation since 2011. Free Field Technologies and MSC Software are part of Hexagon AB since 2017.

Manohar Lal Munjal is an Indian acoustical engineer, honorary professor, and INSA senior scientist at the Facility for Research in Technical Acoustics (FRITA) of the Indian Institute of Science. He is known for his studies on aeroacoustics and finite wave analysis of exhaust systems. He is an elected fellow of all the three major Indian science academies viz. Indian Academy of Sciences, Indian National Science Academy, National Academy of Sciences, India as well as the Indian National Academy of Engineering. He has published three books viz. Noise and Vibration Control, Acoustics of Ducts and Mufflers With Application to Exhaust and Ventilation System Design, and IUTAM Symposium on Designing for Quietness and has contributed chapters to books edited by himself and others. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards for his contributions to Engineering Sciences in 1986.

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