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Sound masking is a technique that is used to render unwanted sound inaudible, making people more comfortable. There are a number of uses for it, ranging from making an open plan office more private and comfortable to work in to making it easier for people in noisy environments to sleep. Several methods can be employed to achieve the technique, ranging from using systems that are integrated into a building to using standalone speakers for direct field masking.
This noise reduction technique is accomplished by playing a consistent, harmonious background sound which drowns out unwanted noise. For an example of how sound masking works, a person can imagine standing in a kitchen with the water running and trying to listen to a conversation in the next room. The noise of the conversation is still present, but the sound of the water overwhelms it. The same principle holds true in sound masking systems.
Sounds of both natural and artificial origin can be used for sound masking. The sound is usually unobtrusive, and designed to be harmonious and pleasant. If people listen for it, they can hear it, but they rapidly become accustomed to the noise, with most people being unaware that a masking system is in use. Systems that project noise through speakers mounted in or from the ceiling are common in big structures, and it is also possible to install individual speakers or white noise machines to control noise pollution in smaller environments.
People use sound masking for a variety of things. Privacy is often an issue, with this technique ensuring that the sounds of private conversations cannot be overheard. It may also be used to muffle sound in a loud environment so that people can concentrate and focus, or so that sounds do not create interference. Call centers, for example, utilize call masking so that phone conversations do not bleed into each other.
Typically, a system is adjustable. The nature of the sound can be changed, as can the volume level and the directionality of the speakers or sound masking devices. Companies that specialize in installing these systems can set them up and set basic levels, and provide information about adjusting it to meet specific needs. People can also install their own sound masking systems, and in a pinch, a crude technique like installing a fountain or playing a white noise recording on a stereo system can be used.
For an ad hoc sound-masking device in a hotel room (to mask next-door or hallway noise) I used to tune the TV to an off-air station. I turned the volume to whatever level I wanted, and covered the screen with a towel to block the light.