Noise-cancelling windows

Noise is frequently cited as one of the leading causes of stress. People living near airports and busy roads complain that they can never relax because of intrusive sounds. Their experiences are reflected in higher levels of mental ill-health, and physical problems like high blood pressure, strokes and heart attacks. Chris Smith spoke with Aman Jindal from the company De-Noize, who might have a better solution...

Aman - In any building, 70 to 80% of your noise enters through your glass because they're the weakest link. And as you mentioned about double glazing, yes it's better than a single glazed window for sure, but they only work in very high frequency regions. When you have this buzzing sound of a tyre on a highway or of planes, the rumbling sound of the engine, those are the low-frequency sounds and they are not stopped by any glass unless the glass is a metre thick and that's just not feasible on windows.

Chris - So when sound hits the house it's basically a pressure wave, isn't it? It's hitting the glass surface and it's pushing the glass in and out and that's making the inside surface of the glass move in and out, so it's basically transmitting that sound into your room, which is why we're disturbed by jets overhead and cars on the road?

Aman - Exactly correct. And if we can cancel these vibrations already on the glass, then you do not hear anything.

Chris - You're trying to make noise cancelling headphones for windows?

Aman - In a sense, yes. Concept wise we do the same thing. We vibrate the window in an opposite phase when we know how it's going to vibrate, and that cancels everything. In essence, it's a very simple thing, whenever we know the centre of the window should be moving towards on the inside of the building, we move it towards the outside of the building and then it cancels each other.

Chris - So you must have some kind of microphone array or some kind of system that is looking at how the window is trying to move when the sound waves hit it, and you're doing some clever processing to work out what force you'd have to put into the glass in the opposite direction so that when the glass tries to move from the sound it doesn't, and then we end up with basically no movement inside so we get basically a quiet room?

Aman - Exactly! The sensors or the actuators that we put are put on the side of the window, so whenever the window vibrates we sense it on its edge and then we input the forces from its edge to vibrate in an opposite way to achieve the cancellation. Those actuators and those sensors, they are combined so they can switch their role so they can at points act like a sensor, and at point act like an actuator.

Chris - How good is it?

Aman - It can achieve up to 90 to 95% additional reduction. On a scale of how the noise is measured, it's measured in a unit called decibel which is a logarithmic scale, we can achieve up to 30 decibel reduction. So 30 decibel is actually a really big reduction, a game changer in this aspect.

Chris - And will it work across-the-board? So does it matter whether it is a chainsaw in the garden, a car going down the road, or a jumbo jet coming into land at Heathrow? It doesn't matter what the sound source is it will still work or are they some things you just can't get rid of?

Aman - A lot of noises are actually stopped by the glass itself, because of a physical barrier. The only thing that's not stopped is these low-frequency noises coming from the jet engine or something like that. And that's the one you hear because that's the weakest thing and we focus on cancelling those, so once they are cancelled you wouldn't hear anything.

Chris - Do you need special glass for this or could you retrofit your system to existing glass? Because glass is expensive.

Aman - It doesn't matter which glass you use, but at the moment how far the technology is it cannot be retrofitted because it's a very complicated process of putting all the sensors and actuators in a specific way.

How we see this on existing windows, people can upgrade it by calling a professional who knows how to put these sensors and actuators in there and then it would work. But we do see our launching market as a new window, a new real estate market where the windows or glass structures would come already fitted with our technology.

Chris - Is it expensive to run? How much energy is going into cancelling out the sound because you've got to put in as much energy that is hitting the building to cancel the sound, haven't you, so it must be consuming quite a bit of energy?

Aman - Our actuators actually run on a very small energy. To give you an example, for a metre square of window you might be spending 10 to 12 watts, which is not a lot of energy.

Chris - And what about price?

Aman - I cannot give you an exact number at the moment, but I can give you a ballpark. We estimate that for a metre square window, which on an average in the UK costs around £500 at the moment a double glazed window, to the end user it might be £650 or £700, but not more than that.

Chris - And how long before this is going to hit the market?

Aman - 14 to 15 months is what where estimating at the moment. We're still developing the tech a bit more and we see that in the next year.