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 or sound power level 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 is unwanted or harmful sound considered unpleasant, loud, or disruptive to hearing. From a physics standpoint, there is no distinction between noise and 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 is a subfield of acoustics dealing with the behaviour of sound in enclosed or partially-enclosed spaces. The architectural details of a room influences the behaviour of sound waves within it, with the effects varying by frequency. Acoustic reflection, diffraction, and diffusion can combine to create audible phenomena such as room modes and standing waves at specific frequencies and locations, echos, and unique reverberation patterns.
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.
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 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 newfound knowledge to the design of Symphony Hall, Boston.
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.
Background noise or ambient noise is any sound other than the sound being monitored. Background noise is a form of noise pollution or interference. Background noise is an important concept in setting noise levels.
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 "Shôn" Eirwyn Ffowcs Williams (1935–2020) 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. The latter tools belong to the field psychoacoustics.
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.
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 an 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 an observer.
The following outline is provided as an overview of and topical guide to acoustics:
In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.
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…"
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.
