Sound masking

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Sound Cover is the addition of sound made by a special digital generator and is distributed by speakers not visible normally through the area to reduce interference or provide confidentiality if required. Sound is a large random band that does not convey information about itself to a listener. This is often called wrong as white noise or pink noise; spectrum and sound levels are specially formed to provide the desired level of privacy by the occupants. Masking operates by covering or covering unwanted sounds, similar to perfumes that mask other odors. This is different from the active noise control technique that tries to remove unwanted sounds. Voice concealment is used in homes, commercial offices, medical facilities, court rooms, and facilities that are safe to provide confidentiality.

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The seminal work covers the subject in detail. Noise is defined as an unwanted noise. It can have three effects depending on the level. At high levels, there are mechanical changes in a person, such as skin warming, rupture of the eardrum, or vibration of the eyeball or internal organs. At a lower level, there are physiological (biological) changes in a person, such as an increase in blood pressure, or stress. At a lower level, changes are psychological (subjective) such as disturbance and complaints. The lethargy is based on factors such as people's evaluation of the noise requirement, or whether it can be controlled, or whether it is normal for the environment (see General Opinions on Voice). The sound masking level is low enough so that they have no known physical or physiological effects on people. One of the purposes of sound masking design is to make the sound "normal", that is, acceptable.

Study of Noise in the Office Environment

Because most voice masking is used in offices, a number of cognitive psychology studies have been made that relate specifically to the office environment. One study found that there was a modest increase in stress (physiology) and reduced motivation caused by distinctive office noise, including speech. It is recommended that the use of sound masking be under the control of the worker. Other studies have shown that level changes are an important factor, but habituation of noise can occur. In the office, habituation can be interpreted as "I am used to noise and it no longer distracts me" or "Because I can not do anything, I have to live with it." Other studies have shown that specific information in speech intrusion is not important nor is the "intensity" (level) of sound between 48 and 76 dBA. Since the level of the louder sound energy is 1,000 times lower, one should assume that the disturbance occurs for all levels. For arithmetic tasks, both oral and non-verbal intrusive sounds lead to significant performance degradation. For "prose tasks" it was found that speech caused a greater performance degradation than a nonverbal vote. In another study, the authors added several significant observations. It was found that "during the serial recall task, the accuracy of the report decreased by 30 to 50%." When intrusive speech is increasingly filtered into meaningless grunts, there is a monotonous increase in performance. Finally, the authors state: "Perhaps the single feature that makes the phenomenon of irrelevant speech so appealing is that sound processing is mandatory; it appears beyond the control of the individual." In the references cited above is a further reference to his earlier work on this subject. There are several implications for sound masking system. Concealment should reduce the difference between a stable background level and a transient level associated with speech and other sounds. Motivation and productivity are improved when this is achieved. The masking sound itself should not change quickly and should be meaningless.

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Closing the sound should satisfy the person who listens to it. People ask themselves a number of questions about the acoustic environment. The following questions are summarized from employee comments about their office environment. These are questions that implicitly ask themselves to determine their response to their environment. The design of sound masking system should take into account this opinion.

• Is the sound made by me or made on my behalf?
• What is the "normal" sound for this environment?
• Is sound required and what can be done to control it?
• Does the sound mean anything?
• Is the voice scary?
• Will that sound have a bad impact on my health?
• How much is the tone of voice?
• How does the room echo?

Noise Complaints

Because voice masking is a random, shaped sound, often incorrectly called "white noise", it is important for sound masking systems to eliminate that sound is actually sound. The most important finding by Kryter is summarized by this statement:

"The general finding that more anxious personality type performance is more affected by voice than non-anxious type will prove a contingency-stimulus factor.In terms of learning or conditioning, the task becomes disliked and is done relatively poorly because it is related or depending on the sound of hostilities. "

"The possible teaching of much of the data presented in this book is that, in addition to being an ear-damaging agent and as a mask of hearing information, noise will not harm organisms or interfere with mental or motor performance."

In a well designed sound masking system, interference caused by foreign conversations (privacy loss) far exceeds the negative response to voice masking

The Quest for Quiet

The biggest problem with masking sounds is when people get annoyed by the activity, their voices are heard (noisy), they are looking for "quiet". They believe that "calm" is a desirable condition of low background sound levels, but what they are really looking for is freedom from acoustic disorders that ultimately lead to interference. The only way to achieve true calm is to maintain a low level of background noise without a transient sound; a condition that requires full isolation of all activity sounds. A better definition of "quiet" is the absence of a disturbing sound, not the absence of all sound. This is the definition used in sound masking.

Steady vs Transient Sounds

The steady sound is a background sound in any environment that is continuous and long-term. If the sound persists for a long time without change, and the level is relatively low, people usually accept it as normal. People rarely realize that the background noise out there is there. Stable sounds can be tonal or random. If the sound is tonal it will create more interference than random noise from the same level because the latter does not convey information to the listener. Transient sounds are conversation, paging, engine sound, and exterior sounds like passing airplanes and road traffic. They are short-term, may vary in levels, and generally distract a person if the level is relatively high against a stable sound level (an increase of about 10 dB is a common criterion). Further redirection is strengthened if the voice has high information content, such as a conversation. At a relatively low level, the main concern is the psychological effects of disturbance and disturbance. The main use of sound masking is to reduce the noise associated with transient sound, and in some cases reduce the clarity of transient sounds (closed offices, secure facilities).

What is a masking?

In the same way that the mask physically covers the wearer's face, the cover covers, hides, or disguises other sounds but does not alter or eliminate them. The actual noise cancellation that removes sounds only works in spatially limited areas, such as headphones, and can not be applied to the entire room. Thus, in a larger space, one can mask a disturbing sound, such as a conversation, by raising the background sound up or above the expected disturbing level. At home, the level required to cover the low sound, and at sporting events, the level was high. The goal is to provide fewer noises without the shutter itself becoming a nuisance, which requires people experienced with this technique to find the optimal level.

Early History of Sound Masking

It is likely that primitive people do not want acoustic privacy, so they never camp near the torrent. They understand that the flow noise will mask the enemy or predator approach. The sound of the fountain in the Roman villas certainly served to cover the sound of an iron-framed wheel on a rocky road. Fountain masking has been taken to a shopping center or building with a large atrium. There was a story about a dentist, in the 1940s, applying a random noise to a patient's ear through earphones to mask the dreadful noise from low-speed exercise. An example of a standalone mask , created in the 1960s, is shown in the picture on the right. The adoption of electronics and the rise of open offices resulted in the rapid evolution of sound masking. The German Quickborner team introduced the concept of open office to the United States in the late 1960s. The Geiger-Hamme Laboratory developed a standard for open office acoustics in the 1970s. It is sponsored by the Public Service Building General Services Administration for use in open government offices. This includes the requirements for sound masking. Many large furniture manufacturers, such as Herman Miller, Steelcase, and Haworth, turn most of their production into open office products. Herman Miller was the first person to have self-contained installed on an open office furniture panel. It does not survive primarily because of the controls available to employees. Owens Corning, a manufacturer of fiberglass products, entered the open office market and introduced a centralized masking system using a speaker called Sweeny baffles. The speaker is unusual because the sound spectrum on the axis is equal to the electrical spectrum. Unfortunately, the axis off the spectrum is different; no longer. Manufacturers of commercial sound systems entered the market in the 1970s; masking is an add-on for other audio products. Soundolier (now part of Atlas Sound) sells self contained masks that endure to date. The Dukane Company sells masks that have two speakers contained in heavy triangular enclosures. Companies that regard masking as their main business appear around that time. One product, Lahti mask, is a speaker mounted on the surface of a plastic ball. Dynasound, Inc. introduces a mask that has speakers mounted on the lid of two gallon paint cans; grip is used for plenary installation. K.R. Moeller Associates sells a standalone mask called Scamp, while Lencore Corporation sells an equivalent unit, now called Spectra. A document was published in 1980 by the Defense Intelligence Agency. This relates to the protection of safe facilities from deliberate audio surveillance; sound masking is one means of protection. Dynasound, Inc. developing vibration devices that can be attached to various surfaces such as doors, walls, and windows, to provide a sound cover. In the 1980s, the Bertagni family developed speakers that were indistinguishable from fiberglass ceiling tiles. The occult is profitable for architects. Attempts were made to use these speakers for sound masking, but the cost and characteristics of the sound beam limited their use for that purpose. Armstrong World Industries, a manufacturer of ceiling materials, developed a similar speaker. This speaker has survived as a Sound Advance product and is now used for applications other than voice masking. The initial attitude among owners, designers, and architects is that covering is the reason for a bad open office design. In the initial system, the installer has no knowledge of how to provide privacy. As a result, many systems only give more noise and are turned off. This is opposed by the advent of companies specializing in the design, installation, and equity, masking system. The evolution of sound masking since 1980 is described elsewhere.

Why Voice Masking is used

Sound cover has several unique advantages over traditional methods to reduce annoying sounds.

1. Sound closure is dynamic (variable) as well as sounds intended to block. The building elements that provide the sound attenuation are static (fixed) and can not adapt to the disturbing sounds that change in the level. Masking can vary from location to location as well as from time to time, to adapt to changing environmental conditions.
2. Voice concealment is by far the cheapest tool to provide privacy.
3. Sound masking system is a special audio system that creates uniform spatial sound levels. Uniformity can be used to integrate music and paging into the system.
4. Sound closure works in the listener's ears and does not rely on building structures (acoustics) so concerns about how disturbing sounds from one place to another are unimportant. Structural modification requires such knowledge and is more expensive.
5. It helps to overcome the sound of the environment, snores the sounds of other family members, It provides a soothing sleeping sound for babies, day and afternoon sleep time is more comfortable; it creates a noise free environment for reading or learning. It provides a personalized and thoughtful environment for covert conversations. There are two groups of people who should not be exposed to sound cover: those with significant hearing loss and those with very limited vision. The first group already has enough privacy that produces masking that gives too much privacy. People with visual impairments use acoustic cues to navigate; sound masking can erase these cues.

Maps Sound masking

Voice Masking App

Commercial Facility

A number of office acoustic studies have been conducted.

Closed office

Closed offices and conference rooms often appear to provide secrecy but are not. Lightweight, or moving, the walls are more transparent sound and most do not extend to the deck of the ceiling, so the speech can go into the plenary ceiling and then to the next office. Sound cover can be used to mask acoustic flaws.

Open office

An open office can have too low background noise levels. Limiting the sound level of the air handling unit is getting tighter. Conversations of others can be clearly understood. Sound cover increases the background level to cover the absence of a wall that will block out the sound.

Less Common Application

Although the above application deals with acoustical privacy in the office, there are applications where sound masking is used to create privacy from the exterior to the office sound. Examples are privacy from elevated highway traffic, sustainable use of sirens in the city, sounds from the floor above, and local construction noise. A voice cover is used in the courtroom to prevent a jury from hearing a lawyer conversation with a judge on a bench.

Medical Facilities

Rule

The United States Congress passed the Health Insurance Portability and Accountability Act (HIPAA) into law. It mandates that individually identifiable patient health information is protected. Although written files and computers must clearly be protected, verbal information should also be protected. "Closed company" (those who must obey the law) should make reasonable efforts to keep the patient informed so as not to be heard. The law itself does not provide specific guidance on how this should be resolved, but documents issued by the Department of Health and Human Services provide some clarification. This includes, as part of the protection, the phrase "what health information is on paper, on the computer, or verbally communicated". The Civil Rights Office has also published a document on the matter, stating that legislation does not require retrofitting space, such as room damping, to comply. As a result, many medical facilities have realized that compliance is prudent and has begun to renovate their facilities. Experience shows that most hospital rooms do not require sound proofing, but can utilize sound masking.

Noise Problem

Noise at the hospital has been a problem for at least fifty years, partly because of the need to have all the hard and clean surfaces. A large number of measurements and reports in prestigious journals have established the problem From the point of view of the patient, the problem is disturbance and disturbance caused by the noise of people, resulting in less rest, worse sleep, and perhaps longer healing time. Increased socialization that is now allowed in hospitals, as well as increased use of medical machinery, has exacerbated the problem. An extensive survey by the Health Service in 1963 showed that patients were often disturbed by speech and distress in other rooms as well as staff visits during the curfew. Other studies concerning sleep disturbance and healing by noise. One study found that the amount and level of increase in sound levels from a constant background was a major contributor to a full awakening or a change in the sleep phase. It is determined that the magnitude of the rate change, regardless of its median value, is more significant than the stable sound level of the same median value. This conclusion is supported by the Environmental Protection Agency document. Suter extends this finding by stating "it is clear that intermittent and impulsive noise is more disturbing than continuous noise from equivalent energy, and that meaningful noise is more likely to produce sleep disturbances than sound with neutral content." This conclusion is the same as that found for open offices.

Sound Masking at Medical Facility

The researchers' findings suggest that privacy issues in medical facilities are very similar to those in open offices. As a result, voice masking has been used profitably in a number of locations. The patient room, corridor, and hospital care area are the main locations. Voting can be used in pension and rehabilitation centers. It is also beneficial in the medical suite or patient contact area of ​​the medical insurance provider. Pharmacies can also provide confidential privacy in the contact area with voice cover.

Safe Facility

Secure facilities require more attention when sound masking is used. For commercial offices and even for medical facilities, listeners for confidential conversations are considered as unusual or unintentional. For secure facilities, listeners are considered deliberate and can use sophisticated technical hearing devices. Many government facilities have used structural solutions, ie rooms (rooms-in-rooms) that are shielded from vibration, acoustics, and electromagnetic surveillance. Unfortunately, not all secret conversations take place in such rooms. The less obvious drawback in a safe space is that modern listening devices can be placed in locations where the building structure can not be protected (inside the wall cavity or remote detection of the window vibration). Another disadvantage in this type of room is that the designer can consider speech to be at a controlled level, but low. Public address systems, speaker phones, and audio/video presentations need additional protection.

Standard

There are many unclassified government documents that determine how safe space is designed. One type of facility is called SCIF (Secure Compartmented Information Facility); any other. There may be confidential documents as well. In almost all documents, sound masking is one of the recommended audio protection methods. There are similar standards that apply to financial institutions.

Category Supervision

There are two categories; each must be handled differently. Uncontrolled areas is where people who try to protect themselves have little or no control over the surrounding environment. This may be all areas outside the building where the safe space is located, such as a parking lot or other public place where it is possible to gain access without detection. Controlled areas are those inside buildings where occupants have size controls.

Signal Type Masking

Unlike sound coverings in offices or hospitals, it should be considered that sophisticated listeners may have the technology to recover the sound buried in a cover sound. To block the device, it may be necessary to provide layered audio protection; several different signals are combined together. The non-stationary random noise must be the first layer; this provides more protection than a standard sound masking generator. Music can be used as a second layer; it was buried under random noise so it was not heard by the occupants of the room. Speech sound generators or actual speech samples can be used as the third layer. The fourth layer, the actual sounds to protect, should be quite buried.

Types of Masking Speakers

The standard masking speakers, discussed in Section 2.1.3 must be equipped with vibration masking to be mounted on a number of surfaces, as mentioned below.

Location for Protection

There are a number of locations where safe facility monitoring can occur.

Windows

Windows generally faces uncontrolled areas (areas that are not under the control of secure facilities). They need protection. Most people do not realize that windows responds well within the speech frequency range. The vibrations caused by spatial speech are minute but can be detected remotely by a laser microphone or directional microphone. The transmitter of the laser microphone system sends infrared signals to the window and the special detector takes reflection. Reflection has been modified by the vibration of the window, so when the fundamental frequency is removed (just like on the radio) the detected vibration is a conversation or other internal sound. The location of the detector should be carefully chosen but the distance can be very far. Directional microphone detects very low level sounds emitted by windows. The emitted sound is diffused, so the microphone angle position is not critical, but the distance to the window should be close enough. For protection, vibration devices are attached to windows that cause windows to vibrate with the appropriate masking signal. This is used to protect against vibration detection and radiated sound detection. The figure on the right shows the relative sound level. The sound emitted in the safe space is not enough to cause interference at normal level conversation.

Walls

Exterior walls are generally made of heavier material than interior walls and rarely require audio protection. The interior wall is a different story. Speech can generate a wall to vibrate and there are multiple locations from which conversations can be detected:

• away from the wall with laser or directional microphone.
• on the far side of the wall with a vibration detector or direct listening.
• inside the wall cavity with vibration detector or fiber optic microphone.

The vibration disguise device provides protection against forms of surveillance when placed indoors to be protected and at the proper height and distance on the wall, consequently, the wall becomes a masking speaker. The sound level diagram in the image on the right shows that masking protects wall panels, wall cavities, and outside walls, while the level of masking in the safe space does not interfere with the conversation.

Doors

The door is a weak link on the wall; they may be hollow or solid core, metal, or specially built for high-velocity attenuation. They can open to an uncontrolled outer area or to an area that is controlled internally. Each door has a gap around its periphery that may have a gasket. Since carpets are often used, there may be a significant gap at the bottom. Most internal door surveillance is done by listening instantly while other methods can be used for external doors. Due to the various sound tracks through and around the door, the sound of vibration is used in the door. The image on the right shows one such installation.

Channels

Listening through the airways is a respected stripping method as almost all modern rooms have a supply channel connected to different rooms. Channels can be effective talk tubes; speech attenuation is very weak in irregular metal channels. In some cases, the drain will connect to an uncontrolled space. Supervision can be done by listening directly or by microphone probe or vibration device inside the channel where they are not visible for inspection. Vibration soundtrack, placed precisely at the boundary of the room, is mounted directly to the metal duct wall and uses the channel wall as a cover speaker. The figure on the right shows the conversation masking on the channel provided by the vibration mask on the wall of the room. External speaker speakers should be used in an appropriate position to transmit sound into fiberglass channels to provide the same protection.

Piping

Typically, fluid-filled pipes do not carry significant speech or pipelines filled with cables. However, the empty drain pipe is an excellent talking tube; vibration cover attached to them. In some facilities, vibration cover has been installed to support pipes and columns.

Raised Floors

The raised floor is generally inaccessible for inspection so supervision can be done there. If the floor is part of the air handling system, the probe microphone or fiber-optic microphone can be effective. If the floor is continuous, high damping of the material makes surveillance with a vibration detector more favorable because the rigid metal plates respond to the conversation. Although the vibration cover can be attached to the floor plate, the preferred protection is to use the speaker cover under the floor.

Plenum Ceilings

The safe rooms often have a suspended ceiling with plenum above. Closing sound through the ceiling material in open offices, so speech can go in the opposite direction into the plenary. It is likely that the perimeter wall extends to the structural ceiling. If the trial is part of the air handling system or if there is penetrating wire penetration, the probe microphone can be used for surveillance. Otherwise, a small penetration can be made to enter this device. As with any commercial office, a plenum speaker mask is installed.

Internal Loudspeaker

Many building codes require the presence of speakers in the safe room for emergency announcements. Although the speakers are intended to create sound, the speaker cone also responds to external sound and the coil produces the minute voltage characteristics of the sound. With proper sensing, that voltage can be converted to speech. While it is possible to place the speaker mask next to the speaker the recommended paging solution is the optical isolator. This is basically an audio diode; sound only goes one way.

Computer Keyboard

There is some evidence that a key sweep sound can be detected to identify the characters entered. A vibration mask placed under the keyboard will emit sufficient masking to block the reconnaissance without disturbing the user.

Personal Apps

Sound masking generators have been used for personal applications for years. There are several device manufacturers for home, hotel, or air travel, especially for sleeping. The figure on the right shows masks that have been on the market for years.

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Sound Status Masking

Progress in Sound Masking

The emergence of sound masking utilizes a variety of components that are typical of other types of sound systems, such as amplifiers and loudspeakers. Since then, the use of masking has grown so that manufacturers add a number of functions to their systems that are useful for sound masking. Some are listed below. Chanaud has given a more detailed discussion.

Initial Ramp Up Function

At the initiation of the sound masking system, it is important not to raise the level of background experienced by existing low-level residents to a higher level of masking abruptly. This function allows the level to be generated slowly and automatically over a period of 30 days.

Fast Ramp Up Function

The building will experience a power outage that closes the masking system. This function prevents the jump level when power is recovered. General recovery time in minutes.

Programmatic Level Control

The need for privacy varies throughout the day. People want privacy during peak hours, but do not need much when occupancy is low at night or on weekends. Security officers do not want privacy when they patrol the office at night. This function automatically and continuously change the overall sound masking during the day. Time history can be different for every day of the week and for each channel masking so it can be used for open and closed offices. This requires pre-knowledge of the activities in the office to be set up correctly. The figure on the right shows an example commonly used for open offices..

Adaptive Functions

Programmed level controls should assume the daily activity level in the office. In many cases this is enough. However, in 2000, Soft dB was the pioneer of adaptive masking control. This function detects actual actual activity levels in real time and automatically adjusts the masking level to minimize interruptions continuously. The image on the right shows the time history of activity level (environmental noise) in the open office and the masking voice response to the activity. Changes in the masking level should be slow enough so that the residents are not noticed.

Addressable Function

Older masking sound systems require visits for major adjustments after the initial setup. The newer masking systems now have the ability to be adjusted remotely, either locally or over the internet. Due to this additional capability, the system has software that can customize masking levels in zones, small groups of speakers, or even individual speakers. Some can also adjust the spectrum of masking to this level. Some of these systems have maps of available system zones that identify zones or loudspeakers to modify. This function eliminates the need for older monitor panels, simplifies the tasks of facility managers, and the cost of contractor visits.

Rapid Equalization

The performance of voice masking as a privacy tool is determined by the precise arrangement of system and spectrum levels (equalization, adjustment). Incorrect settings have been the cause of system rejection in the past. One reason is that the levels and spectra in the zone are set iteratively. One person measures the spectrum and the other manually adjusts the generator frequency bands, a slow and unreliable process. Software has been developed that allows a number of spectra to be measured in zones and averaged appropriately. An average can be uploaded to the generator and internally compared to the desired spectrum. Then the generator automatically adjusts its electrical output to provide the correct acoustic spectrum in the zone. Uploading can be done with physical or remote connections.

Successful Sound Masking System Attribute

There are a number of factors that contribute to the success of sound masking systems. Good design takes into account each of these factors; systems with more of them will last longer.

Sound Masking Level

The system should be able to produce sounds that cover the clarity of sound for different levels of privacy. It should also be able to cover the sound of aircraft, vehicle sounds, dog barks, neighboring music, and other sources of interference if needed. To do this, the equipment must have various levels and the number of zones sufficient.

Sound Masking Spectrum

The system should be able to apply different masking spectra in different locations. To do this, the system must have sufficient number of channels to adjust the required spectrum. Speakers in open offices, closed offices, and vibration masking all need a different spectrum.

Spatial Uniformity

Spatial uniformity of voice masking in, or in between, closed offices is generally not a concern. How is spatial uniformity in open office defined? There are two ways: (1) require the overall A-weighted sound level to be fairly constant over a certain area, and; (2) requires that the variations in the masking spectrum be minimized. The most successful systems use the preceding requirements; the strict spatial uniformity of the spectrum is very difficult to achieve except when phasing is of concern (see Lesson below). Uniformity of sound masking is only important in areas that are geometrically and uniformly similar. In some zones, different panel heights and requirements for speech privacy uniformity may suggest different levels of masking. Also there are conditions that suggest intentional level changes (See Soundscaping below). Deviation from uniformity must be done with caution. The initial requirement is for detailed measurements on a number of workstations showing variations of levels below a certain number, such as/- 2 dB (A). Most occupants of workstations are more concerned with the sounds of others and are willing to accept some level of variation within their own areas. A successful system is a system in which the passageways in which people walk meet the requirements of uniformity; changes there happen faster and more visible. The best uniformity is achieved by placing the right masking speakers during installation and inspection and adjustment of equipment prior to occupancy.

Temporal Variability

In the initial system, digital masking generators experience short-term rate changes; cycle time is so short that the same sound is repeated over and over again. As a result, some specifications require uniformity of time in the short run. This issue is bypassed with the requirement to use an analog generator that creates a completely random sound. The problem has been designed so far that almost all masking generators now create a digital signal that only the audience can interpret as random. Now, the masking sound in the short term has a constant level. The same is not true for longer periods. The occupant's privacy needs vary throughout the workday and the only variable that can accommodate this is sound masking. For hours with a high level of activity, the person will need more masking to maintain his privacy. At low activity levels, such as the early curfew, the person wants to be aware of the presence of others; community needs in part exceeds the need for privacy, so the masking rate should be lower. If the building has a mobile security officer after office hours, no need for privacy and sound masking levels should be minimized. The successful system has a clock and control function that will continuously vary the mask level with a small rise for twenty-four hours and for each day of the week. There are two types. One where programmable level variations are first and one where the actual activity's voice rate is measured and the masking level is set automatically to create the required privacy. View the programmatic level controls and adaptive functions listed above. The unsuccessful system has a switch controlled by an unused clock ON-OFF.

When two adjacent speakers are connected to create an identical masking sound, listeners passing between the midpoints between them can detect a "rustling" sound. This relates to phase relationships at various frequencies. This negative effect is most noticeable when the cable speakers of this way are placed in plenary over fiberglass ceiling tiles, or when placed face down on a suspended ceiling. A system that manages to avoid these negative effects. In many cases with lower NRC or higher CAC ceilings, or under elevated floors, branched tree cables with the same signal to all speakers are acceptable. If there is concern about this effect, the cable is altered so that two independent masking channels are fed to the checkered cable circuit as shown in the picture on the right. Alternate speakers have masking signals that are unrelated to others. Inspection is required to ensure the cabling is correct. In some current systems, the cable connecting each speaker is a cable that carries several channels of masking and the feeding channel of each speaker is selected to avoid this effect.

Sound Diffusion

Lighting engineers for years must face the glare, visual discomfort caused by direct lighting. They develop Equivalent Sphere Illumination to measure it. They then developed the Visual Comfort Convenience . High comfort values ​​imply more widespread illumination; light comes from different directions. The concept was never applied seriously to the sound. Most people are constantly experiencing an ambient sound and rarely notice it if the level makes sense; often referred to as background sounds. That's because the sounds they hear come from many sources, the sound field is scattered. This concept applies to sound masking as well. Experience has shown that when an office resident can point to a source of sound masking (the field of sound is more direct), acceptance is reduced. Diffusion of masking sound is best accomplished by the sound of weakening materials, such as ceilings and floors. From the location listed above, under the floor cover creates the best diffusion.

Wide Tools

System manufacturers should have sufficient number of types, sizes, and speaker shapes to accommodate masking applications, possibly on the same project. The system should be able to handle indoor and outdoor applications, large plenaries, small, or no plenary, and large or small access floor cavities. Both the loudspeaker and the vibration device must be available. For the location of the visible mask, the shape and color of the speakers should be acceptable to the owner. The system should be able to include paging and music; it improves the utility of the system and provides economic benefits to the users. The system should be able to equalize the spectrum and level at least in each zone.

User Acceptability

Closure of the voice must be received by the listener. Masking that is really the most acceptable background see below). Incorporating advanced functions, mentioned above, improves user acceptance. Masking must achieve the purpose of privacy by having an acceptable level. This is a more difficult factor because system installers rarely have control over two other factors that determine privacy. The exchange of information between team members during the design helps improve acceptance. Realistic privacy goals are very important. When other privacy factors can not be combined with a reasonable level of masking to achieve the desired privacy, the privacy goals should be changed.

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The masking sound should be completely background so it does not attract attention to itself. spectrum masking should be random and neutral, not too low or high frequency noise. Rate changes, if desired, should occur slowly. Spatial uniformity reduces the level of openness. Equipment should not be visible; this includes inaccessibility for the control and concealment of speakers.

Centrally Controlled

The system must be centrally controlled both manually and remotely. All controls must be available for the installer; a limited number of controls must be available to the owner, and not to employees. The controls available to owners only have to be those who change the level. They have to step (not analogue) and have small steps and a limited range of levels so that proper system functionality is maintained. Manual control is acceptable if the cabinet or room can be locked. A computer-controlled software interface is preferred because passwords can be used.

Cost

The cost of masking system equipment should be comparable with other sound systems. Equipment should be designed to minimize installation costs.

Expandability

The system must be ready for development. Centralized systems should have excessive cabinet space, backup zone control, and adequate power capacity. Distributed systems require only the correct power outlet for expansion.

Compliance Code

The system must comply with local building codes as well as national and international standards.

Soundscaping

In most environments, sound levels change gradually as people move from one place to another. Gradual changes are more acceptable than fast change. The same goes for sound masking. People who move from a masked area to a non-binocular area will notice a change of level as they go. This usually happens when moving from an open office area to a corridor or to an uninventioned support area such as for a printer or photocopier. This incident violates the design rules that sound masking should not attract attention to itself. This event can be avoided by changing the sound level gradually. This is done by adding a speaker string, each of which is consecutively reduced in level to a non-binocene background.

Masking System Types

There are several types of masking systems.

• Portable system . This system is small and can be installed temporarily. They are centrally controlled and empowered. They are used for Privacy Secrets in rental space, and can be used for demonstration purposes elsewhere.
• Standalone system . This is usually a single, or multiple, single unit that contains all the features needed to create a masking sound. Each unit is supported by standard line voltage and no centralized control, but they are portable. They are used at home, on a table, and can be carried in luggage for privacy in hotel rooms.
• Centralized system . They can be of any size but preferably used in large permanent installations. They can contain sophisticated features mentioned above, centered, and centrally controlled.
• Distributed system . These systems can be any size but are distinguished from centralized systems by the fact that they may be centrally controlled, but the power for speakers is distributed throughout the area.

Masking System Components

All masking systems consist of several basic components. The main component is the source of one or more random electrical signals. Usually the source can make a pink or white sound. This particular spectrum is rarely accepted by the listener when converted to masking sound, so the spectrum equalizer is needed to create the exact sound spectrum that the listener hears. Most professionals recommend equalizer cover at least the talking frequency range from 160 Hz to 8000 Hz in 1/3 octave band; most products cover a wider range. Additional signals, such as paging and music, can be added from outside sources. These electrical signals are rarely precise when converted into sound, so a more limited spectrum equalizer must be added. All signals are added in the mixer to adjust their relative level and then sent to one or more power amplifiers. From amplifiers, mixed signals are sent to devices that control the overall level in different areas called zones and from there to loudspeakers or vibration devices to create sound. Many newer masking systems attach all components to amplifiers in a fairly small cabinet, which can be either shelves, shelves, or mounted tables. There may be more than one of each component in any system and from one system in a large facility. The latest system design has incorporated the ability to control many components by software, both locally and remotely. See the dashed line in the image. The advantage of such control lies in its simplicity with the various component settings can be changed. The disadvantage is the additional cost of adding this control, especially if system changes are rarely needed.

Array Speaker Masking

Offices that require sound cover, especially open office, can have a shape other than a rectangle. if the office is large, making arrays manually can be boring. Some companies have developed programs that can automatically create speaker arrangement based on the dimensions and shape of the room and the desired vertical location of the speakers (See Section 2.1.3). This program can be used to help develop the list of materials and provide a mold for the installer to find each speaker. The sample prints are shown on the picture on the right for the office with the elevator center. The vertical and horizontal locations of each speaker are displayed in the printout as well as channel, zone, and speaker settings. In cases where tap settings vary, the speaker form changes.

Horizontal Spacing Spacing and Vertical Location

The horizontal distance from the masking speakers in commercial facilities has a strong impact on project costs. If the speaker is too close, the cost is higher but the uniformity is good. If the speakers are too far, the cost is lower but the uniformity and acceptance of the masking are compromised.

• The distance for speakers in a suspended ceiling plenary is determined by:

Ceiling Heavens. The gypsum ceiling allows for wider distances while fiberglass requires a shorter distance.

Height of Ceiling Height. The higher ceilings allow for greater distances.

Plenary Depth. Deeper plenaries allow for wider distances.

The sound absorbs the batt in the plenum. Batt needs a shorter distance.

For 3-foot plenum and standard mineralized tiles NRC 0.55, 15 ft is the default distance.

• The distance in an open session is determined by:

Height of structural ceiling. The higher ceilings allow for greater distances.

The sound absorbs the propeller. Batts need a shorter distance.

• The typical distance for the face down facing speakers is 12 feet to fit the standard 2 ceiling tile shape by 4.
• The distance for speakers under the floor is determined by:

High cavity: The deeper cavity allows for greater distances.

Air grille: Distance is determined by its existence.

In Suspended Ceiling plot

Plenary is the space between the suspended ceiling and the structural deck above it. Since most offices have such space, speakers cover the sound usually added there. For open office, uniformity of voice masking in the occupied area is important and is largely determined by the horizontal distance of the masking speakers as described above. Array speakers are generally rectangular. They are generally facing upwards to reflect sound from the deck and expand the sound distribution to create a more uniform sound field. The diagram on the right shows an example. For a closed office, sound level uniformity is not a problem. Generally, ceiling tiles with high transmission losses are recommended, which has a CAC (Ceiling Atenuation Class) rating of 30 or greater. This reduces the impact of sound closure in adjacent open areas that will have excessive levels in those offices. Usually the ceiling plenum is used as a return air channel that requires an open grill. Closing of votes in plenary over closed offices can result in excessive levels. There is a simple metal cover placed over the grille to reduce the impact of the hole. Available large enough so as not to block airflow. The top and left images show the masking speakers mounted directly on the ceiling tile grid. The two lower numbers are examples of speakers hanging on the ceiling plenum. If the pleno ceiling is shallow, a low profile speaker is required. These speakers emit sound horizontally rather than vertically to improve masking uniformity in the area occupied below. An example is shown in the bottom left image.

In the Open Ceiling

In some offices, especially warehouses that have been converted into office space, there is no ceiling plenum. Masking speakers are hung in a manner similar to those above suspended ceilings but the distance and height of the speakers are different. Usually, the speakers are mounted higher and the distance between the two is closer. The height of the above structural ceiling is a big factor in distance, such as the presence or absence of sound absorbing material on the surface of the ceiling. Uniformly good masking sound can be achieved. Some office designs use the use of scattered ceiling tiles (clouds) (counterclockwise). Careful design is required to achieve reasonable masking uniformity.

Under the High Floor

A voice masking speaker can be placed under a high floor in an office that uses it. To carry the weight on top, the floor material is structurally robust and offers a high sound attenuation beneath it. Experience has shown that not only is the sound uniformity excellent, but the occupants are hard pressed to determine where the sound source is (good diffusion-See Section 3.7.6). The figure on the right shows a sound level of masking at 48 inches above the floor; they are all within 1 dB each other. One way is the line between the speakers; the other direction is the lateral line to the speakers starting at the midpoint. If the depth of the cavity is sufficient, normal sound masking speakers may be used, otherwise small speakers may be used; they enter into the cavity as small as 2 inches and emit the sound horizontally. If the cavity is used as a return air channel, care should be taken to protect the opening.

Face Down in Suspended Ceiling

Unlike the closing speakers above the suspended ceiling or under the elevated access floor, the cover sound from the face-to-face speakers runs directly to the listener without the benefit of an annoying sound suppressor. The face-down speakers have been, for many years, typical for paging and music systems, but are now used more recently in some voice masking applications. Initially, the goal is to minimize the speaker's visibility by having a tile act like a ceiling as a masking speaker. It was first introduced by Bertagni and later commercialized by Armstrong Company. The picture on the top right shows the plenary view of this mask. The down side seems to be standard fiberglass mineral tile. Because so many devices pierce the ceiling, the translucent viewer of this speaker appeals to architects. The technical difficulty in developing this product is expanding the masking deployment to address the lack of intervention materials, but the masking spectrum can be tailored to that typical of those recommended by consultants. More recent development is facial recognition. The subsurface speaker is much smaller than that used for paging systems. The picture below shows this mask. Because the small size of this mask has a masking spectrum that is not in the range of spectrum recommended by the consultant. See the recommendations section below. These speakers are often referred to as speakers direct fields to distinguish them from other arrays that emit sound indirectly through interfering materials. Although speaker locations in the previous section are often preferred to improve voice and reception diffusion, there are situations where direct field speakers are beneficial. Alternate location for small speakers mounted on the wall.

Installed at the Top of Panel

Masking Speaker has been installed at the top of the panel for several years. Mostly attributed to Herman Miller's furniture system. The initial version has a rounded ball with the speakers facing up on it mounted. The ball is placed on a short rod connected to the top of the furniture panel. The sound radiated upward and reflected from the ceiling tiles. Each mask has volume and spectrum controls that can be accessed by people on both sides of the panel. Since most open offices have multiple panels, the exact distance from the cover is not a problem. The effectiveness of masking is somewhat determined by the sound absorption characteristics of the ceiling tiles. The mask is then replaced by the maker shown in the picture on the right; central level and spectrum control.

In Unusual Location

In some old buildings the location above does not exist. Vibration masks have been applied in a number of facilities. One application is used on the ceiling of the gypsum board; the entire gypsum panel becomes the speaker. They have also been attached to the air supply channel, emitting masking through air diffusers. In other cases, the mask is hidden above the air duct on the open ceiling. Masking speakers have been placed under the table, beneath the surface of open office work, and behind the painting. The figure on the right shows the speaker covering the wall.

Two Design Rules

1. The closing should be placed by the listener. Inexperienced people often want to put masking by the speaker. This will require them to speak louder or closer. This will not effectively disguise the listener.
2. Every effort must be made to make the system really into the background, not to convey any information exposed to it.

Two Design Objectives

1. The closing sound should be random and incoherent; meaningful voice should not be used. The sound from adjacent speakers should have no correlation with each other. This is best accomplished in two ways: (1) by having intervention materials (eg the ceiling) between the speaker and the listener; or (2) adjacent speakers are signaled from different masking sources.
2. The sound field should be as free as possible to reduce awareness. Material intervention helps in this direction.

Sound Masking

CHANNELS: The number of places where the frequency spectrum of masking can be set. For commercial facilities, one channel is required for each of the different speaker locations recorded in Section 2.1.3. For secure facilities, one channel is required for each of the different speaker locations recorded in Section 2.3.5.

ZONES: The number of places where the overall masking level can be set (generally in terms of dB (A)). Levels can be set along with the spectrum across multiple generators. It can also be set on any power amplifier that is attached to any number of masking speakers. Speakers can be subdivided into zones by using several attenuators attached to each amplifier. Finally, each masking speaker should be able to control the individual level. In a sense, every speaker can be made into a separate zone. The main purpose of detailed controls is to compensate for variations in levels caused by local geometric influences, such as the airways. In some sophisticated systems, zone controls can be performed centrally.

Public open office level

Many of the measurements on privacy provided by various height panels have resulted in recommendations for overall masking levels. They are for Normal Privacy with fiberglass ceiling tiles and no clear flanking lines.

• Panel Height: less than 150 cm (59 inches) Level: 48 dB (A)
• Panel Height: near 150 cm (59 inches) Level: 47 dB (A)
• Panel Height: close to 170 cm (67 inches) Level: 46 dB (A)
• Panel height: near 180 cm (71 inches) Level: 45 dB (A)
• Panel Height: near 200 cm (79 inches) Level: 44 dB (A)

Spectrum public open office

The sound masking spectrum shown in the table to the right is the overall level of 47 dB (A). This is the default level and can be customized based on office design. For a higher or lower level, add or subtract 1 dB on each frequency. See the recommendations above. The selected spectral contour is based on a variety of measurements and is the average value based on the spectrum used by many consultants. See the top image on the left for an example of the range of spectrum used. The importance of spectral contours is shown in the lower figure on the left where the various spectra m

Source of the article : Wikipedia