What is Noise Cancellation?

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Noise cancellation technology is a growing field that capitalizes on the combination of disparate technological advancements. The purpose of the technology is to cancel or at least minimize unwanted sounds. Modern lives seem full of all sorts of noise, some of which are dangerous to our ears. In fact, many people, especially those who live and work in cities, have very little quiet time during the day.

Noise cancellation technology aims to remedy the excess noise that we experience. Of course there already are low-tech solutions to the problem. Ear-plugs and sound dampeners are available, but they are not very convenient nor very efficient. Noise cancellation tries to 'block' the sound at the source instead of trying to prevent the sounds from entering our ear canals.

But how does it work? Sounds travel through the air, or through liquids in the form of waves, and each of those waves has a particular shape. Noise cancelling technologies first rely on small microphones that detect the sounds in a given environment. A digital signal processor determines what sound wave is required to cancel the unwanted sound wave and then it creates that sound and amplifies it through speakers or headphones. One way to understand this is to imagine a 'positive' sound and a 'negative' sound created at virtually the same time, and these two sounds cancel themselves out thereby bringing the listener closer to silence.

These technologies are in their early stages, and they cannot completely omit sounds, but improvements are consistently being introduced. The hope is that one day that these technologies can be used to minimize all sorts of unwanted sounds around us. Imagine, for example, a lawn mower, hair dryer or vacuum cleaner that included a noise cancelling system, thereby greatly reducing the unpleasantly loud sounds.

Noise cancelling headphones are already available. The headphones cancel out unwanted ambient sounds allowing the listener to focus solely on the music. The latest versions of these noise cancelling headphones work suprisingly well, and new applications are certainly on the horizon.

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Posted by: anon2217
Are any systems being developed which can help counter noise outdoors? And if so who by?
Posted by: jsweet
It occurred to me that noise cancellation technology relies on the ability to generate a complimentary signal where its output would be 180 degrees out of phase with the incoming signal. Virtually impossible in a single unit due to the delays inherent in the circuitry. Would it be possible to design a system which would pick up the sound (a train), transmit it to a receiver some distance away, and have that receiver overlay the complimentary signals in real time to cancel the noise at the end. I see this as a way to silence unwanted noise for entire neighborhoods. A main station which receives the sound, re-transmits the complimentary signal at a speed greater than the speed of sound, and each remote location (house, room, yard, etc...) has a receiver which syncs up the signals and generates the complimentary sound to cancel the noise. Is there a company doing this at this time? Shall I get a patent?!
Posted by: anon5869
Hi Jsweet, you might be on to something. Here are two additional thoughts...

* If the issue is an inheret delay, could we somehow tap into a harmonic opposite of a sound at a higher frequency

* Create a profile called train that has the basic sound of a train. Then install it at the desired locations. Even though it's not perfect cancellation it would certainly serve to dampen the sound.

I do have two counter arguments, especially if you you are looking for pure cancellation. The first is minor: If you record the sound of a train in one place it may not sound the same as it will further down the track. The net effect I assume would be a dampening effect, and I think that would be effective.

The second, in terms of a train and to some degree traffic is more significant: A train, and highway traffic for that matter create a significant amount of seismic noise that in turns vibrates nearby structures and causes new sounds.

In business terms this criticism might serve you well because you can sell a better solution customized for every house than you can sell in a one size fits all solution. You can also sell ongoing support for keeping the quality of dampening consisitant as sound conditions change.

Larry Boeldt

Posted by: anon8964
Surely if this is going to work at an individual house level, it is necessary to measure the 'incoming' noise profile at the house in question and produce the 'negative' anti-noise locally?

I would think the biggest problem here is to achieve this processing quickly enough and to project the ant-noise sound so that it has a broad 'sweet spot'.

Posted by: anon11356
Very interesting technology... Does anyone think it could be implemented in a room/pod?

Thanks


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