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Active Noise Cancelling Revolution
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Active Noise Cancelling Revolution
Damping unwanted noise is a request that has arose from many sides. For families to rest easy, musicians to play in quiet rooms, scientist to have a vibration free laboratory and also for applications were stealth is crucial.

While for long time this need has been answered by passive isolation, now the door to active and intelligent countermeasures is opening. Anocsys, a mid sized swiss enterprise founded in 2004 is thereby leading the way.

The principle

Sound is a pressure wave and therefore subject to interference phenomena. It is possible to cancel sound, by applying a 180° phase shift copy of the actual sound. While in theory pretty simple, producing this negative interference has been a great challenge for decades. Environment noise is hardly predictable, consists of many frequencies and has a complex structure in space.

Active noise controlling usually focuses on the low frequencies, as they are easier to calculate and compensate, and high frequencies can easily be damped by passive structures. Another reason is, that human voice uses mid to high frequencies and should not be cancelled. Noise control often includes vibration control. Here no stress is put on this aspect, as it is limited to surfaces and solids.

To produce the counter-sound field one or more speaker have to be combined with microphones, a microprocessor and an appropriate algorithm. Of which especially the last two components have recently advanced greatly.

The beginnings

The first practical applications were noise cancelling headphones for pilots in the early 1950s. On one hand, airplanes and helicopters produce a very stable and predictable noise. On the other hand, headphones offer a small, well known volume in which the sound has to be controlled and an active speaker is part of the design anyway. The time is also no coincidence, as then electronic circuits became powerful enough to calculate counter sound for such a simple case.

After this first success, noise controlling headphones evolved slowly, but almost no other applications used sound cancelling.

The revolution

Being limited to a small, well known volume, noise cancelling has recently become available for much bigger spaces.

Anocsys, a swiss high-tech enterprise has now developed an active noise cancelling system for living rooms. Microphones create a perimeter around the object, resulting in very high outside noise suppression. The system is able to reduce environment noise to inaudible levels and is especially effective for low frequencies. This includes airplane and train, as well as car noise. Within a house, the setup is operational even if the windows are open, bringing relief e.g. to families living near airports.

But of course living rooms are only the beginning and many other applications of the underlying setup and know-how are obvious.

The future

Besides of countless situations were a certain space has to be isolated from environment noise, the opposite has also huge potential. Many common devices are a great source of noise and would be more attractive if they became quieter. Imagine a plane whose engine sounds are cancelled by an active noise control. With airplane noise becoming a bigger political issue an economical dimension is also clearly visible.

Finally, noise cancelling is an extreme form of sound controlling, which also can be a very interesting option. What if your simple Fiat Punto would sound just as the newest model from Maserati? Cancel the old sound and overlay a cooler one. While this is not commercially available yet, the research from Anocsys and other institutions makes this much more probable.

Noise cancelling is also intriguing for military recon activities. Silent submarines, planes and vehicles are certainly on the wish list of modern armies. Active noise control has the potential to revolutionize and change many aspects of what nowadays is so normal, that most people cannot even think of it being different. What today sounds like science fiction could become reality within a couple of years.

By Pablo Dörig, a current ETHZ student and an active Synetgizer

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