Equipment to reduce noise through noise cancellation. Credit: DLR
Hard to believe? The underlying principle is simple: If you superimpose two sound waves of the same frequency and volume so that the crests of one wave meet the troughs of the other wave, the two waves “extinguish” each other. It is hoped that by using this technology in aeroplane engines, the resulting noise levels will be reduced. You will learn about important parameters of acoustic waves. You will use a model fan – a fan is the first stage in an aeroplane’s engine – to find out how sound is generated and how it can be manipulated through active noise reduction.
Quieter times are coming
Who amongst us has not experienced this: Aeroplane noise so loud you can hardly hear yourself think or air conditioning in offices that force you into shouting to make yourself heard. Our ears seem to be particularly sensitive to some kinds of noises and these drown out everything else.
Scientists have found ways to reduce a lot of noise: They know how to reduce the din coming from engines or air conditioning. They have developed active headphones that extinguish homogeneous background noise. Pilots use this in the cockpit and some passengers do the same on long-haul flights. By using “sound design”, you can make your purring 12-cylinder car sound like a roaring monster or block out engine noise completely.
Targeting the root of the problem
Active noise control equipment. Credit: DLR (CC-BY 3.0)
“If I had to do my homework with building site noise in the background, I would have different problems at once. If I put my hands over my ears, I wouldn’t be able to write and I also wouldn’t be able to hear my phone ringing. If I used ear plugs, I’d be able to use my hands, but otherwise my problems would remain. Sound-absorbing windows would be useful, but I don’t like working with my windows closed, as the air tends to get stuffy. There must be a method that targets noise as it is made!”