![Example of airborne and structure-borne transmission of sound, where Lp is sound pressure level, A is attenuation, P is acoustical pressure, S is the area of the wall [m2], and t is the transmission coefficient Sound-transmission.png](http://upload.wikimedia.org/wikipedia/en/thumb/c/c6/Sound-transmission.png/300px-Sound-transmission.png)
Acoustic transmission is the transmission of sounds through and between materials, including air, wall, and musical instruments.
The degree to which sound is transferred between two materials depends on how well their acoustical impedances match.
Musical instruments are generally designed to radiate sound effectively. A high-impedance part of the instrument, such as a string, transmits vibrations through a bridge (intermediate impedance) to a sound board (lower impedance). The soundboard then moves the still lower-impedance air. Without bridge and soundboard, the instrument does not transmit enough sound to the air, and is too quiet to be performed with. An electric guitar has no soundboard; it uses a microphone pick-up and artificial amplification. Without amplification, electric guitars are very quiet.
Stethoscopes roughly match the acoustical impedance of the human body, so they transmit sounds from a patient's chest to the doctor's ear much more effectively than the air does. Putting an ear to someone's chest would have a similar effect.
Acoustic transmission in building design refers to a number of processes by which sound can be transferred from one part of a building to another. Typically these are:
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.
The stethoscope is a medical device for auscultation, or listening to internal sounds of an animal or human body. It typically has a small disc-shaped resonator that is placed against the skin, with either one or two tubes connected to two earpieces. A stethoscope can be used to listen to the sounds made by the heart, lungs or intestines, as well as blood flow in arteries and veins. In combination with a manual sphygmomanometer, it is commonly used when measuring blood pressure.
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.
An anechoic chamber is a room designed to stop reflections of either sound or electromagnetic waves. They are also often isolated from energy entering from their surroundings. This combination means that a person or detector exclusively hears direct sounds, in effect simulating being outside in a free field.
Soundproofing is any means of impeding sound propagation. There are several basic ways to reduce sound: increasing the distance between source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles for absorption, or using active antinoise sound generators.
A sound board, or soundboard, is the surface of a string instrument that the strings vibrate against, usually via some sort of bridge. Pianos, guitars, banjos, and many other stringed instruments incorporate soundboards. The resonant properties of the sound board and the interior of the instrument greatly increase the loudness of the vibrating strings. "The soundboard is probably the most important element of a guitar in terms of its influence on the quality of the instrument's tone [timbre]."
When the [guitar] top vibrates, it generates sound waves, much like a loudspeaker. As the soundboard moves forward, the air that is in front of it is compressed and it moves away from the guitar. As the soundboard moves back, the pressure on the air in front of the guitar is reduced. This is called a "rarefaction," and air rushes in to fill the rarefied region. Through this process, an alternating series of compression and rarefaction pulses travel away from the soundboard, creating sound waves.
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.
A sound attenuator, or duct silencer, sound trap, or muffler, is a noise control acoustical treatment of Heating Ventilating and Air-Conditioning (HVAC) ductwork designed to reduce transmission of noise through the ductwork, either from equipment into occupied spaces in a building, or between occupied spaces.
Sound Transmission Class is an integer rating of how well a building partition attenuates airborne sound. In the US, it is widely used to rate interior partitions, ceilings, floors, doors, windows and exterior wall configurations. Outside the US, the ISO Sound Reduction Index (SRI) is used. The STC rating very roughly reflects the decibel reduction of noise that a partition can provide. The STC is useful for evaluating annoyance due to speech sounds, but not music or machinery noise as these sources contain more low frequency energy than speech.
Acoustic 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'.
An acoustic horn or waveguide is a tapered sound guide designed to provide an acoustic impedance match between a sound source and free air. This has the effect of maximizing the efficiency with which sound waves from the particular source are transferred to the air. Conversely, a horn can be used at the receiving end to optimize the transfer of sound from the air to a receiver.
Noise control or noise mitigation is a set of strategies to reduce noise pollution or to reduce the impact of that noise, whether outdoors or indoors.
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.
An acoustic waveguide is a physical structure for guiding sound waves.
Vibration isolation is the process of isolating an object, such as a piece of equipment, from the source of vibrations. Vibration is undesirable in many domains, primarily engineered systems and habitable spaces, and methods have been developed to prevent the transfer of vibration to such systems. Vibrations propagate via mechanical waves and certain mechanical linkages conduct vibrations more efficiently than others. Passive vibration isolation makes use of materials and mechanical linkages that absorb and damp these mechanical waves. Active vibration isolation involves sensors and actuators that produce disruptive interference that cancels-out incoming vibration.
QuietRock is a brand of constrained-layer damped gypsum panels manufactured in Newark, California, by PABCO Gypsum. QuietRock was developed in 2003 by Kevin Surace and Brandon D. Tinianov, the first sound-reducing gypsum wallboard panel for use in the building construction industry. QuietRock panels are engineered to increase sound transmission loss (STL) performance and, consequently, the Sound Transmission Class (STC) rating for building partitions using sound and vibration theory.
An acoustic guitar is a musical instrument in the string family. When a string is plucked, its vibration is transmitted from the bridge, resonating throughout the top of the guitar. It is also transmitted to the side and back of the instrument, resonating through the air in the body, and producing sound from the sound hole. The original, general term for this stringed instrument is guitar, and the retronym 'acoustic guitar' distinguishes it from an electric guitar, which relies on electronic amplification. Typically, a guitar's body is a sound box, of which the top side serves as a sound board that enhances the vibration sounds of the strings. In standard tuning the guitar's six strings are tuned (low to high) E2 A2 D3 G3 B3 E4.
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.
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.
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.