Sometimes clients will ask us if our systems are “active noise control”. The simple answer is that active noise control uses a different acoustic principle to sound masking. But it’s good to understand the specifics.

What does sound masking do?

Sound masking adds a randomised sound to a space to increase the ambient background sound levels. This reduces the intelligibility of speech and reduces the impact of intrusive noise. The sound can be tuned or shaped depending upon the ambient sound levels within the space. However, this does not cancel noise.

For more detailed information on how sound masking works, check out our previous blog posts, in particular this one.

What is active noise control?

Active noise control, also known as “active noise cancellation” uses “phase cancellation” to generate sound waves targeted to unwanted sounds.

These systems use a microphone to pick up particular sound levels and frequencies. An amplifier then processes these sounds and generates opposing sound waves. The target sounds and opposing sound waves cancel each other when they meet.

An example of this is the noise cancelling headphone. Here, within the enclosed space between the headphone shell and the ear, the phase cancellation happens. This is why you cannot hear the “noise” of the airplane when you’re wearing noise cancelling headphones. The sound waves have been cancelled within the headphone.

Another example is in certain high end vehicles. Noise cancellation is possible because the space is enclosed, and the driver is fixed in place.

Why not use ANC in office spaces?

The acoustics of each space is not fixed. Where in headphones the space within the headphone remains constant, or in a car, where the driver and passengers are mostly stagnant, offices are not. The acoustic environment of the office changes from moment to moment, interfering with any potential phase cancellation.

If you have an open plan office, for example, the acoustics of the room changes every time anything moves. Moving a chair has changed the acoustics of the room. A colleague walking through the office changes the acoustics as well. With current technology, it is no possible to cancel sound within such spaces.

Conclusion

While active noise cancellation or control would theoretically be a real boon to noisy spaces, reality has other plans. Sound masking is a good option for spaces where intrusive noise is a problem.