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.
Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.
Ultrasound is sound with frequencies greater than 20 kilohertz. This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz.
Noise pollution, or sound pollution, is the propagation of noise or sound with ranging impacts on the activity of human or animal life, most of which are harmful to a degree. The source of outdoor noise worldwide is mainly caused by machines, transport and propagation systems. Poor urban planning may give rise to noise disintegration or pollution, side-by-side industrial and residential buildings can result in noise pollution in the residential areas. Some of the main sources of noise in residential areas include loud music, transportation, lawn care maintenance, construction, electrical generators, wind turbines, explosions and people.
Infrasound, sometimes referred to as low frequency sound, describes sound waves with a frequency below the lower limit of human audibility. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. Although the ear is the primary organ for sensing low sound, at higher intensities it is possible to feel infrasound vibrations in various parts of the body.
Acoustical 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.
Whales use a variety of sounds for communication and sensation. The mechanisms used to produce sound vary from one family of cetaceans to another. Marine mammals, including whales, dolphins, and porpoises, are much more dependent on sound than land mammals due to the limited effectiveness of other senses in water. Sight is less effective for marine mammals because of the way particulates in the ocean scatter light. Smell is also limited, as molecules diffuse more slowly in water than in air, which makes smelling less effective. However, the speed of sound is roughly four times greater in water than in the atmosphere at sea level. As sea mammals are so dependent on hearing to communicate and feed, environmentalists and cetologists are concerned that they are being harmed by the increased ambient noise in the world's oceans caused by ships, sonar and marine seismic surveys.
Acoustic homing is the process in which a system uses the sound or acoustic signals of a target or destination to guide a moving object. There are two types of acoustic homing: passive acoustic homing and active acoustic homing. Objects using passive acoustic homing rely on detecting acoustic emissions produced by the target. Conversely, objects using active acoustic homing make use of sonar to emit a signal and detect its reflection off the target. The signal detected is then processed by the system to determine the proper response for the object. Acoustic homing is useful for applications where other forms of navigation and tracking can be ineffective. It is commonly used in environments where radio or GPS signals can not be detected, such as underwater.
Hearing range describes the frequency range that can be heard by humans or other animals, though it can also refer to the range of levels. The human range is commonly given as 20 to 20,000 Hz, although there is considerable variation between individuals, especially at high frequencies, and a gradual loss of sensitivity to higher frequencies with age is considered normal. Sensitivity also varies with frequency, as shown by equal-loudness contours. Routine investigation for hearing loss usually involves an audiogram which shows threshold levels relative to a normal.
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.
Sound from ultrasound is the name given here to the generation of audible sound from modulated ultrasound without using an active receiver. This happens when the modulated ultrasound passes through a nonlinear medium which acts, intentionally or unintentionally, as a demodulator.
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.
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.
Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory science.
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.
Seismic or vibrational communication is a process of conveying information through mechanical (seismic) vibrations of the substrate. The substrate may be the earth, a plant stem or leaf, the surface of a body of water, a spider's web, a honeycomb, or any of the myriad types of soil substrates. Seismic cues are generally conveyed by surface Rayleigh or bending waves generated through vibrations on the substrate, or acoustical waves that couple with the substrate. Vibrational communication is an ancient sensory modality and it is widespread in the animal kingdom where it has evolved several times independently. It has been reported in mammals, birds, reptiles, amphibians, insects, arachnids, crustaceans and nematode worms. Vibrations and other communication channels are not necessarily mutually exclusive, but can be used in multi-modal communication.
Plant bioacoustics refers to the creation of sound waves by plants. Measured sound emissions by plants as well as differential germination rates, growth rates and behavioral modifications in response to sound are well documented. Plants detect neighbors by means other than well-established communicative signals including volatile chemicals, light detection, direct contact and root signaling. Because sound waves travel efficiently through soil and can be produced with minimal energy expenditure, plants may use sound as a means for interpreting their environment and surroundings. Preliminary evidence supports that plants create sound in root tips when cell walls break. Because plant roots respond only to sound waves at frequencies which match waves emitted by the plants themselves, it is likely that plants can receive and transduce sound vibrations into signals to elicit behavioral modifications as a form of below ground communication.
Biotremology is the study of production, dispersion and reception of mechanical vibrations by organisms, and their effect on behavior. This involves neurophysiological and anatomical basis of vibration production and detection, and relation of vibrations to the medium they disperse through. Vibrations can represent either signals used in vibrational (seismic) communication or inadvertent cues used, for example, in locating prey. In almost all known cases, they are transmitted as surface waves along the boundary of a medium, i.e. Rayleigh waves or bending waves. While most attention is directed towards the role of vibrations in animal behavior, plants actively respond to sounds and vibrations as well, so this subject is shared with plant bioacoustics. Other groups of organisms are also postulated to either actively produce or at least use vibrations to sense their environment, but those are currently far less studied.
