The Fundamentals Of Active Noise Cancellation

By Author: Henry Janice
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Whenever I am asked what I do in a social environment, I have to get ready for a lot of blank looks. Initially, I would answer in an outspoken way that we create active noise cancellation systems and Noise Barrier Walls for the heavy industry.

This was followed by a long silence until someone asks whether I use Sound Control Curtains or not. A layman when confronted with the term of active noise cancellation, all they truly hear is noise cancellation, and they fall back on the past experience to assist them categorize what I do, that usually implies insulation.

In the past few years, active noise cancellation has become more common due to the incredible endeavors of the companies that manufacture active noise cancellation headphones. There is still a substantial amount of confusion regarding what precisely active noise cancellation is and how it is different from passive noise cancellation products like insulation. The purpose of this post is ...
... to try and describe those differences in a way that is both understandable and accessible to all.

The fundamentals

In simple words, passive noise cancellation treatments are all bout deflection and absorption. They are in essence a barrier between the noise source and the observer. Passive treatments take the shape of foam lining between the interior and engine of a car, foam plugs in the ear, and even the 20 foot concrete barrier walls that line busy streets. Their main purpose is to either absorb the sound, and turn it into something else or reflect it in another direction.

On the contrary, active noise cancellation depends on the principle of destructive interference, the idea of using a single wave to cancel another wave. The simplest way to visualize this principle is to use waves in water. If I drop a stone in the pond, it will create ripples. By dropping a second stone in the pond shortly after the first one, as the ripples from every rock intermingle, small areas are created where there are no waves visible. As a matter of fact, those points the surface is completely smooth. This is a sign of destructive interference.

Why use active rather than passive

Passive treatments have a realistic lower threshold at a point they provide zero or limited reduction. The lower limit is controversial, but for the most part, passive treatments suffer from lessened efficiency at about 1000 Hz and their performance falls as the frequency gets lower.

Conclusion

Although active noise cancellation is a sophisticated solution to undesired noise just like acoustic doors, it is never a substitute of top quality foam. Due to the costs associated with every system, we suggest doing everything possible with passive types of treatment and then evaluate your ambience before deciding to apply active noise cancellation.