Noise Canceling Earphones

Written by Robert Mac
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Noise canceling earphones do exactly what they claim to: they actually cancel background noise. If you attach one to a cell phone, you can chat away in a noisy bar and hear every word--and so will the person you're talking to. Noise canceling earphones work because of one of the most basic audio properties: sound waves.

Noise Canceling Earphones Create Opposite Sound Waves

Picture a sound wave: it has high and low points, just like an ocean wave. If two waves coming from the same direction line up--look out!--you're going to get soaked when this double-sized wave crashes on top of you. Now picture two ocean waves approaching each other from opposite directions-they cancel themselves out.

The same is true of sound waves: if two waves of opposite frequencies line up just right, they will cancel themselves out. This process, called destructive interference, allows us to create anti-noise to block out unwanted background sounds. All you need is to monitor the background noise with microphones, create an opposite wave with a fast-acting amplifier, and pass the resulting sound on to the ear.

And this is exactly what noise canceling earphones do. Tiny microphones pick up the offending ambient sound and cancel it out. You can listen to your CDs on the bus while the annoying whine of the bus engine and the drone of other traffic are significantly lowered to a more comfortable level.

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