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Masking Sound is the addition of generated sound (commonly, though inaccurately, referred to as "white noise" or "pink noise") into an environment to mask unwanted sound. It relies on auditory masking. Masking sound is not an active noise control (noise cancellation technique). Masking sound reduces or eliminates perception of sound. The technology is promoted as a widespread application to an entire area to improve the acoustical satisfaction, by improving the acoustical privacy of the space. This improves one's ability to focus and their productivity.
Masking sound is analogous to light. - Sound Power and Luminosity - Sound Intensity and Light intensity - They both have spectral characteristics.
'Masking Sound' is promoted as reliable, consistent, accurate and precise solution to control of background sound in the built environment. There is significant and misplaced prejudice towards background sound (in contrast to background noise). However, there is substantial evidence produced and published by Beranek (BBN) and Cavanaugh (et al., 1962 Speech Privacy in Buildings) indicating that acoustical satisfaction of a space cannot be guaranteed without consideration of each of the three principle parameters of architectural acoustical design, formalized and established in the early 1900s by Sabine. The three principle parameters are known as the 'ABCs' of architectural acoustics: - A for Absorption -- Sufficient (but not in excess) absorption in the built environment. - B for Blocking -- Sufficient isolation of the built environment. - C for Control -- Control of background sound levels in the built environment. No single technique is effective in addressing every sound transmission path (direct, reflected, diffraction, transmission) and varies in performance on a case-by-case basis.
'Masking Sound' produced by a sound masking system can be used to reduce the impression of intruding sound (reducing annoyance, distraction). It can be used the improve acoustical privacy, synonymously used as speech privacy. However, there's a fundamental misconception in the deployment of a sound masking system in treating areas where there's failure in appreciating the difference between the perception of privacy and speech privacy.
Sound masking systems are often relied upon as a basis of design upon with Sound Transmission Class (STC, as supported by ASTM E336) or Noise Isolation Class (NIC, as supported by ASTM E336) to ensure an appropriate level of privacy between contiguous rooms. Various organizations (ASTM, ASA/ANSI, GBI, LEED, ASHRAE, WELL, etc.) define unique categories for labeling of acoustical zones with purpose and/or function.
Typical classifications consider:
Masking sound is an effective solution in masking intruding noise. The masking sound spectrum (National Research Council of Canada's COPE curve) is generated to be comfortable and elevated in level to be conducive to acoustical privacy in the built and occupied environment and can be specified up to 48dBA (Warnock in Acoustical privacy in the landscaped office in 1973). It may be used as a noise control solution to mask unwanted noise such as intermittent sound from machinery (within the overall limits and spectra). Masking sound seeks to reduce the intelligibility of sound from a source by reducing the signal-to-noise ratio. It is an effective solution to promote compliance with HIPAA and GLBA regulations.
However, the masking sound produced by electroacoustical system may also be disruptive if the sound masking system is improperly designed, improperly commissioned, or not verified by a professional acoustician.
A number of cases exist where sound masking has been successfully installed for exterior applications, the most common target of concern being roadway noise. In one example application a large artificial waterfall was constructed as part of the garden exterior of an urban hotel in Santa Rosa, California. The waterfall cascades down an extensive wall approximately four meters in height and functions both for sound masking and as a physical barrier to road noise.
The plenum is the space between a “dropped” ceiling and the upper deck for the floor. In-Plenum sound masking systems, which employ a network of loud speakers located completely within the plenum, were the first such systems developed – they have been in use since the 1960s. Plenum-based speakers typically range from 4” to 10” inches in diameter and generally face upwards, towards the upper deck. This is done to reflect sound from the speakers to broaden, as much as possible, the footprint from the speaker in the work area. This promotes a spatially uniform delivery of sound, reducing the perception of directivity.
As with any commercial grade sound masking system, an in-plenum sound masking system requires proper layout design, commissioning, and verification of the performance. Disregarding the importance of any of these stages in implementation will result in a sound masking system that does not perform according to the specifications of an acoustician. Only the most sophisticated sound masking systems can control the background sound level and spectra of masking sound accurately and precisely throughout a space, made only possible with smallest zones (spatial limits around a speaker) and sophisticated electronics and software.
Uniformity can be achieved by adjusting the acoustic output of individual or small groups of speakers. Adjustments routinely include changes in output volume and output spectra of individual speakers. To provide this adjustment capability, additional system electronics for individual speakers or for small groups of speakers are required.
Direct Field sound masking systems have been in use since the late 1990s. The name takes after the mechanics of sound transmission which considers the "direct sound path" from the loudspeaker emitted towards the recipients (listeners) underneath. Initially used as an accessory for open office cubicles, direct field systems have been fully integrated into at least one open office furniture system and have been designed to be installed both in dropped ceilings and in offices without any absorptive ceiling systems. When installed in dropped ceilings, direct field systems use speakers that are mounted facing down. When a ceiling tile is not available, they are mounted facing down on any available structure, sending the masking noise directly into the intended space.
Theoretically, direct field system would benefit from speakers that are omni-directional, meaning that they transmit energy equally in essentially all directions. However, direct field systems require tighter arrays of loudspeakers given the polarity of the emission of sound. Direct field speakers do not preclude the need for sound level adjustment nor spectral tuning - a misconception.
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.
Reverberation, in psychoacoustics and acoustics, is a persistence of sound after the sound is produced. A reverberation, or reverb, is created when a sound or signal is reflected causing 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.
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.
Soundproofing is any means of reducing the sound pressure with respect to a specified sound source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles, or using active antinoise sound generators.
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.
The Noise Reduction Coefficient is a single number value ranging from 0.0-1.0 that describes the average sound absorption performance of a material. An NRC of 0.0 indicates the object does not attenuate mid-frequency sounds, but rather reflects sound energy. This is more conceptual than physically achievable: even very thick concrete walls will attenuate sound and may have an NRC of 0.05. Conversely, an NRC of 1.0 indicates that the material provides an acoustic surface area that is equivalent to its physical, two-dimensional surface area. This rating is common of thicker, porous sound absorptive materials such as 2"-thick fabric-wrapped fiberglass panel. Materials can achieve NRC values greater than 1.00. This is a shortcoming of the test procedure and a limitation of how acousticians define a square unit of absorption, and not a characteristic of the material itself.
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.
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 Sound Reduction Index (SRI) ISO index 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.
A dropped ceiling is a secondary ceiling, hung below the main (structural) ceiling. It may also be referred to as a drop ceiling, T-bar ceiling, false ceiling, suspended ceiling, grid ceiling, drop in ceiling, drop out ceiling, or ceiling tiles and is a staple of modern construction and architecture in both residential and commercial applications.
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.
A loudspeaker enclosure or loudspeaker cabinet is an enclosure in which speaker drivers and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4" woofers and small tweeters designed for listening to music with a hi-fi system in a private home to huge, heavy subwoofer enclosures with multiple 18" or even 21" speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts.
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.
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:
Tinnitus maskers are a range of devices based on simple white noise machines used to add natural or artificial sound into a tinnitus sufferer's environment in order to mask or cover up the ringing. The noise is supplied by a sound generator, which may reside in or above the ear or be placed on a table or elsewhere in the environment. The noise is usually white noise or music, but in some cases, it may be patterned sound or specially tailored sound based on the characteristics of the person's tinnitus.
Soundscape ecology is the study of the acoustic relationships between living organisms, human and other, and their environment, whether the organisms are marine or terrestrial. First appearing in the Handbook for Acoustic Ecology edited by Barry Truax, in 1978, the term has occasionally been used, sometimes interchangeably, with the term acoustic ecology. Soundscape ecologists also study the relationships between the three basic sources of sound that comprise the soundscape: those generated by organisms are referred to as the biophony; those from non-biological natural categories are classified as the geophony, and those produced by humans, the anthropophony.
Acoustic plaster is plaster which contains fibres or aggregate so that it absorbs sound. Early plasters contained asbestos, but newer ones consist of a base layer of absorptive substrate panels, which are typically mineral wool, or a non-combustible inorganic blow-glass granulate. A first finishing layer is then applied on top of the substrate panels, and sometimes a second finishing layer is added for greater sound attenuation. Pre-made acoustic panels are more commonly used, but acoustic plaster provides a smooth and seamless appearance, and greater flexibility for readjustment. The drawback is the greater level of skill required in application. Proprietary types of acoustic plaster developed in the 1920s included Macoustic Plaster, Sabinite, Kalite, Wyodak, Old Newark and Sprayo-Flake produced by companies such as US Gypsum.
Noise curves are a common way to measure and specify background noise in unoccupied buildings and spaces. Their purpose is to produce a single-value representation of a complete sound spectrum. International standards organizations recognize the need to objectify judgements on the amount of ambient noise in enclosed spaces, and provide us with definitions for various noise curves. The ANSI/ASA S12.2-2008 standard, for example, recommends an NC value of 25-35 for schools and 15-18 for concert halls.