If you spend much time traveling by plane, train or bus, or if you work in a noisy office environment, you might have considered trying out some noise-canceling headphones. Since these headphones block out ambient noise, you can hear what you want to hear without cranking up the volume and potentially damaging your eardrums.

How do noise-canceling headphones work? It’s not magic, although it might feel that way when you’re sitting on the plane next to a screaming baby.

The excellent site HowStuffWorks offers a great in-depth explanation of the science behind noise-canceling headphones. It all began on a long flight in 1978. Amar Bose was trying to pass the time with some music, but the noise from the jet engines was so loud he could barely hear his tunes. Bose started working on some calculations right there on the plane, trying to figure out how to reduce ambient noise using headphones. Ten years later, his noise-canceling headphones appeared on the market.

So how did he do it? It helps to understand a bit about sound waves. As the article explains, sound waves are longitudinal waves with "compressions" and "rarefactions." (A compression corresponds to a crest, and a rarefaction corresponds to a trough.) Your ear detects sound waves, and then your brain interprets the sounds. 

Noise-canceling headphones come in two types: active and passive. Passive types use layers of sound-absorbing material to help reduce outside noise. At best, passive headphones will decrease the noise by about 15 to 20 decibels (dB). Meanwhile, on a plane you’re dealing with 75 to 80 dB of noise in the cabin just from the jet engines. That’s where you want to have active noise-canceling headphones. They start with the same structural barriers, but then they go beyond simply blocking the sounds. Active noise-canceling headphones do exactly what their name says: they actively cancel out the incoming sound waves. 

How do they do that? They use something called destructive interference. Strangely enough, active noise-canceling headphones cancel out the sound waves by creating more sound waves. These waves mimic the incoming waves, only the compressions and rarefactions are arranged in opposite positions, so that the compressions on one wave line up with the rarefactions of the other. The result is that these waves cancel each other out, and your ears and brain hear none of it.

In order to make this all happen, the headphones use a microphone and electronics inside the ear cup to “hear” and measure the outside noise and then create a new wave to counteract it. A speaker sends out this destructive interference without disturbing what the listener really wants to hear. The result is that good quality noise-canceling headphones can reduce noise by about 80 dB, making them ideal for air travel or any place with high background noise levels.

The HowStuffWorks site has some great diagrams and information about sound waves, transducers, speakers and different types of headphones. So if you want to learn even more, you can check out the article for yourself. You can even test what you’ve learned with the Noise-canceling Headphones Quiz.

On the other hand, if you just want to find some great noise-canceling headphones at reasonable prices, check out our selection. And as always, if you have any questions or would like some help figuring out which headphones will work best for you, feel free to contact us.