Though the terms are often used interchangeably, noise cancellation and sound masking utilize different technologies and are used for different purposes.
Technically speaking, it is nearly impossible to truly "cancel" noise in a typical human environment, due to the highly variable and dynamic nature of most living and working space. However, you can come close if you are able to isolate and control the noise from the greater environment. Headphones are frequently used for this purpose. Settings in which the ambient sound frequencies are relatively static and easily predicted, such as on an airplane, or close to a particular machine, are appropriate for noise cancellation technology. Noise canceling headphones or speakers assess the current ambient sounds, and generate a tone with the inverse wavelength, which in effect cancels out all sounds of the targeted wavelength.
Homes, offices, stores, and most other human environments display a highly dynamic range of sound frequencies, making it very difficult and costly to monitor and cancel frequencies in the manner of typical noise cancellation technology. Also, it is beyond the scope of most if not all existing noise cancellation technologies to differentiate between
undesirable background noise (chatter), and useful human vocalization (desirable communication). It would clearly be unhelpful to cancel or otherwise scatter
all human speech in a home or office.
Sound masking
masks (as the name implies) rather than cancels sounds. You have probably experienced the effects of sound masking in your home when you stand at the kitchen sink with the water running, and try to talk with someone across the room. The sound of the running water makes it difficult to clearly understand the person talking. Once you turn the tap off, you can once again hear the conversation clearly. Running water masks human speech very well, without distracting or annoying the listener, because it creates a random, yet relatively uniform sound, within a specific frequency spectrum.
To be effective, sound masking systems must generate sound that is both random and within a specific range of frequency and decibels. Typical humans will actively listen to sounds that form a recognizable pattern, like music or speech, but will tune out sounds that they can't make sense of, like static (unless the sound becomes too loud). In an office, sound masking works by injecting a random, low-level background noise that correlates in frequency to typical human speech, making it difficult to understand conversations outside of the listener's immediate area. Care must be taken to insure that both the decibel level and frequency of the sound masking system is appropriate for the environment. If the sound masking is set too loud, or at the wrong frequency, occupants may have a negative response.
To set the sound masking to the appropriate levels, the office must first be assessed for it's existing acoustical qualities, which include the size of the office, the physical materials of the office (walls, ceilings, doors, partitions, etc.), the furniture in the office, the number of occupants and their normal functions (customer service, engineers, managers, etc.), typical background noise levels in the office (
HVAC, copiers, computers, etc.), and purpose of the office space (quiet work area, team work area, call center, meeting room, etc.). Depending on the circumstances, the system can be tuned for greater speech privacy (for example, a work area that requires mental concentration with little distraction) or lesser speech privacy (for example, a collaborative work area, where employees hold informal meetings as well as work independently).
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