Noise Cancellation vs. Sound Masking

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).

Degrees of Speech Privacy: How much is enough?

When it comes to office acoustics, design follows function. Every human space has different acoustical requirements, depending on its purpose. We expect it to be quiet in a library, and noisy at a basketball game. The acoustical design of each space has (hopefully) been tailored to its function. Like libraries and gymnasiums, office space benefits from acoustical design that has been tailored to its specific purpose.

There are five generally recognized degrees of speech privacy:

1. No speech privacy
2. Transitional
3. Normal
4. Confidential
5. Secret

No Speech Privacy

In environments where face-to-face conversation is the major activity, speech privacy isn't typically desirable, since of course the purpose of a conversation is to hear and understand one another. Retail space, restaurants, lecture halls, and reception areas are examples of areas that don't typically benefit from speech privacy.

Transitional Speech Privacy

Transitional levels of speech privacy allow for transmission of auditory information, but make it slightly more difficult to clearly understand human speech. Casual office layouts with mixed use areas (often used to develop a "team" feeling in the office) generally provide Transitional speech privacy. Though it may feel more like home to have a couch and coffee table in the middle of the work area, it will also sound more like home, too. Depending on the office culture, this may not be a bad thing, but it may lead to an unprofessional atmosphere unless carefully planned and monitored.

Normal Speech Privacy

Most office workers find that Normal speech privacy levels help them to focus on their work, without distraction. Normal privacy allows for auditory transmission, but makes it difficult to understand conversations outside of the employee's immediate area. Office areas in which people are typically working alone at their desks will benefit from Normal privacy levels. The majority of office space falls into this category, though there is a large degree of acceptable variance within the Normal range.

Confidential Speech Privacy

In situations where privacy is important, either for personal, professional, or legal reasons, Confidential speech privacy is recommended. Conversations that you would typically have "behind closed doors" require Confidential privacy levels, ensuring that human speech is completely unintelligible to listeners outside of the conversation.

Secret Speech Privacy

As the name implies, Secret privacy levels make it extremely difficult or impossible for outside listeners to overhear a conversation, even with listening devices. Though it may seem like the stuff of James Bond movies, there are situations in which organizations require complete secrecy in order to protect their interests and prevent information leaks.