Noise Cancellation Technology

Headphones and earphones that feature active noise reduction (ANR) use noise cancellation technology. How does it work, and what is it good for?

Sound energy is a waveform. So, in conceptual terms, if two sound waveforms are the exact mirror image of each other, when added together they cancel each other out, and the result is no sound. The aim of noise cancellation technology is to dynamically produce a sound wave that is the mirror image of a noise that is undesired, thereby cancelling it out. The noise is not merely blocked out or masked over; sound energy is actually eliminated from the environment. A headphone that features active noise cancellation includes a microphone on the earpiece to detect the incoming sound signals of the external (unwanted) noise. A battery-driven circuit generates the inverted wave on the fly, and adds it in to the music signal that is delivered to your ear. The generated sound signal acts to cancel out the background noise from the external sources.

In practice, the technique works best for continuous, low-frequency noise, such as the low droning sound in an airplane cabin. It does not work for intermittent noise such as speech, or higher pitched noises such as the wailing of a baby. For more effective attenuation of these types of sounds while listening to music, try a noise-isolating in-ear headphone (canalphone) instead.

In addition to its application in headphones, earphones, and headsets, noise cancellation is used in active mufflers, to reduce noise and vibration of machinery, and to create quiet zones in cabins and passenger compartments of planes, trains, and automobiles.

* If you are truly curious and of an experimental bent, you can demonstrate the noise cancellation principle for yourself with two speakers attached to a Windows PC, using software you can download here.

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