Saving the World by Destroying Evil Sound Waves

I'm going to write my first post that actually contains some Physics - you have been warned!

Yesterday I talked about avoiding my Physics essay and this evening I actually finished it. It was quite interesting once I got into it and started using my other favourite website (since yesterday it is now demoted to second favourite... I talk about you new first favourite website here), howstuffworks and I actually understood what I was doing!

The essay was supposed to be all about noise and how to reduce it, I'm not exactly sure that my teacher wanted more than half of it to be taken up by noise cancelling headphones but it was so cool I just couldn't help myself!

The headphones 'destroy' background noise by using small microphones to detect the noise (any sound wave outside of the headphone) and then replicate the waves. The replicated wave has the same width and height (frequency and amplitude) as the original sound wave. However the wave is rotated by 180 degrees so when it is emitted the peaks (convex part) of our new wave aligns with the troughs (concave part) and vice verse so they look like the image where the orange line is one wave and the pink line is the other wave. This causes them to cancel out and so no outside noise is heard within the headphones.

The noise is now cancelled! Of course I realise that sound waves are longitudinal and not transverse so this must be a simplified explanation but this is cool right?! The sound practically disappears!

I guess maybe the title exaggerates slightly but Noise Induced Hearing Loss is a serious problem! At least that's what I read on the Internet... Everyone knows the Internet is always right!