Friday, November 17, 2017

How Noise Cancelling Headphones Actually Work

As the story goes, noise canceling headphones were the brainchild of electrical engineer Dr. Amar Bose, founder of the world-famous Bose Corporation. Reportedly, while on a commercial airline flight from the Zurich to Boston in 1978, Dr. Bose was given a brand new electronic headset that the airline was then offering to replace the older tube-type headsets previously supplied to passengers for listening to in-flight entertainment programs.

These new headsets were the same ones sold along with Sony Walkman Music Players brought out at that same time. They were lightweight and comfortable and, from an acoustic engineer's perspective, represented what should have been a great improvement for listeners confined to a cabin during a multi-hour transatlantic flight. According to Bose, however, the experience was a total disappointment. The ambient noise from the airplane engines and other sounds within the passenger area of the plane was so loud it made it difficult to clearly hear the music coming through the headphones. It was then that Bose had an “aha moment” in a sudden flash of inspiration he immediately began to put down on paper as the design that could possibly solve the problem.

Stop the Noise With Noise

The sketches made on that airplane flight became the basis for the first noise-canceling headphones, developed during the next decade by a group of engineers Bose put together in the Boston area. The idea was to cancel sound with sound by developing headphones capable of “listening.”

Two Types of Noise Canceling Headphones

JVC Noise-Cancelling Headphones with Retractable Cord

JVC Noise-Cancelling Headphones with Retractable Cord



Essentially, all headphones have some noise canceling capability simply because they either fit over your ears or sit inside your ear holes, thereby blocking out a certain amount of exterior sound. This is called passive noise cancellation, which is further enhanced by the use of sound-deadening foam in the ear-cups that will naturally block out some degree of noise.

Active noise canceling technology, which is what Bose envisioned on that fateful flight, utilizes passive noise cancellation along with an electronic means of canceling sound with its “opposite” sound. Sound travels in waves, with peaks and troughs. Active noise canceling headphones have a microphone built into the earpieces that amplify external sounds. Special circuitry within the headphones then creates a sound wave identical to what's being picked up by this microphone, except this wave is 180° out of phase (or opposite). By placing these two waves atop one another the sounds cancel each other out through phenomena called “destructive interference.”

Stop the Noise

Destructive interference works especially well on lower frequency sounds like what's experienced riding in planes and trains, and allows you to hear the sounds you want to hear through your headset much more clearly. Noise canceling headphones also operate to simply provide you with a peaceful silence without any music or other amplified sounds coming through. Some fine examples of noise-canceling headphones on offer at JustHeadphone.com include these JVC sets capable of 18.5 dB noise reduction at 200Hz or 12 dB noise reduction at 300Hz.