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 feedback is a positive feedback situation that may occur when an acoustic path exists between an audio input and an audio output. In this example, a signal received by the microphone is amplified and passed out of the loudspeaker. The sound from the loudspeaker can then be received by the microphone again, amplified further, and then passed out through the loudspeaker again. The frequency of the resulting howl is determined by resonance frequencies in the microphone, amplifier, and loudspeaker, the acoustics of the room, the directional pick-up and emission patterns of the microphone and loudspeaker, and the distance between them. The principles of audio feedback were first discovered by Danish scientist Søren Absalon Larsen, hence it is also known as the Larsen effect.
Reverberation, in acoustics, is a persistence of sound after it is produced. Reverberation is created when a sound or signal is reflected. This causes numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air. This is most noticeable when the sound source stops but the reflections continue, their amplitude decreasing, until zero is reached.
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.
Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener. Its first application was in movie theaters. Prior to surround sound, theater sound systems commonly had three screen channels of sound that played from three loudspeakers located in front of the audience. Surround sound adds one or more channels from loudspeakers to the side or behind the listener that are able to create the sensation of sound coming from any horizontal direction around the listener.
An echo chamber is a hollow enclosure used to produce reverberation, usually for recording purposes. For example, the producers of a television or radio program might wish to produce the aural illusion that a conversation is taking place in a large room or a cave; these effects can be accomplished by playing the recording of the conversation inside an echo chamber, with an accompanying microphone to catch the reverberation. Nowadays, effects units are more widely used to create such effects, but echo chambers are still used today, such as the famous echo chambers at Capitol Studios.
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.
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.
Loudspeaker acoustics is a subfield of acoustical engineering concerned with the reproduction of sound and the parameters involved in doing so in actual equipment.
Digital room correction is a process in the field of acoustics where digital filters designed to ameliorate unfavorable effects of a room's acoustics are applied to the input of a sound reproduction system. Modern room correction systems produce substantial improvements in the time domain and frequency domain response of the sound reproduction system.
In acoustics, absorption refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Part of the absorbed energy is transformed into heat and part is transmitted through the absorbing body. The energy transformed into heat is said to have been 'lost'.
Acoustic foam is an open celled foam used for acoustic treatment. It attenuates airbone sound waves, reducing their amplitude, for the purposes of noise reduction or noise control. The energy is dissipated as heat. Acoustic foam can be made in several different colors, sizes and thickness.
Loudspeaker measurement is the practice of determining the behaviour of loudspeakers by measuring various aspects of performance. This measurement is especially important because loudspeakers, being transducers, have a higher level of distortion than other audio system components used in playback or sound reinforcement.
Meyer Sound Laboratories is an American company based in Berkeley, California that manufactures self-powered loudspeakers, multichannel audio show control systems, electroacoustic architecture, and audio analysis tools for the professional sound reinforcement, fixed installation, and sound recording industries.
Acoustic enhancement is a subtle type of sound reinforcement system used to augment direct, reflected, or reverberant sound. While sound reinforcement systems are usually used to increase the sound level of the sound source, acoustic enhancement systems are typically used to increase the acoustic energy in the venue in a manner that is not noticed by the audience. The correctly installed systems replicate the desired acoustics of early reflections and reverberation from a room that is properly designed for acoustic music. An additional benefit of these systems is that the room acoustics can be changed or adjusted to be matched to the type of performance. The use of acoustic anhancement as electronic architecture offers a good solution for multi-use performance halls that need to be "dead" for amplified music, and are used occasionally for acoustic performances. These systems are often associated with acoustic sound sources like a chamber orchestra, symphony orchestra, or opera, but have also found acceptance in a variety of applications and venues that include rehearsal rooms, recording facilities conference rooms, sound stages, sports arenas, and outdoor venues.
LARES is an electronic sound enhancement system that uses microprocessors to control multiple loudspeakers and microphones placed around a performance space for the purpose of providing active acoustic treatment. LARES was invented in Massachusetts in 1988, by Dr David Griesinger and Steve Barbar who were working at Lexicon, Inc. LARES was given its own company division in 1990, and LARES Associates was formed in 1995 as a separate corporation. Since then, hundreds of LARES systems have been used in concert halls, opera houses performance venues, and houses of worship from outdoor music festivals to permanent indoor symphony halls.
William M. Hartmann is a noted physicist, psychoacoustician, author, and former president of the Acoustical Society of America. His major contributions in psychoacoustics are in pitch perception, binaural hearing, and sound localization. Working with junior colleagues, he discovered several major pitch effects: the binaural edge pitch, the binaural coherence edge pitch, the pitch shifts of mistuned harmonics, and the harmonic unmasking effect. His textbook, Signals, Sound and Sensation, is widely used in courses on psychoacoustics. He is currently a professor of physics at Michigan State University.
In live sound mixing, gain before feedback (GBF) is a practical measure of how much a microphone can be amplified in a sound reinforcement system before causing audio feedback. In audiology, GBF is a measure of hearing aid performance. In both fields the amount of gain is measured in decibels at or just below the point at which the sound from the speaker driver re-enters the microphone and the system begins to ring or feed back. Potential acoustic gain (PAG) is a calculated figure representing gain that a system can support without feeding back.
Diffuse field acoustic testing is the testing of the mechanical resistance of a spacecraft to the acoustic pressures during launch.
Apparent source width (ASW) is the audible impression of a spatially extended sound source. This psychoacoustic impression results from the sound radiation characteristics of the source and the properties of the acoustic space into which it is radiating. Wide source widths are desired by listeners of music because these are associated with the sound of acoustic music, opera, classical music, and historically informed performance. Research concerning ASW comes from the field of room acoustics, architectural acoustics and auralization, as well as musical acoustics, psychoacoustics and systematic musicology.
