ADVERTISEMENT
  About the SA Blog Network













PsiVid

PsiVid


A cross section of science on the cyberscreen
PsiVid HomeAboutContact

How do Active Noise Canceling Headphones Work?

The views expressed are those of the author and are not necessarily those of Scientific American.


Email   PrintPrint



I’ve been traveling quite a bit recently and the drone of the plane engine is a major annoyance. While I have a pair of noise dampening ear buds which are much more comfortable and produce better sound than the default iPhone earbuds, I have been wavering about purchasing a pair of active noise canceling earphones for myself.

Although I understand the physics (and accompanying math–specifically trigonometry) of how the earphones work, I was uncertain if the technology was sophisticated enough to cancel ambient noise for the average flyer at a reasonable price.

Curiosity about the practicality of spending so much money for these contraptions led me to ask several frequent fliers their opinions. Overall, they expressed resounding enthusiasm for the devices, so I did some further research. When I learned Bose had created active noise canceling headphones for astronauts on the space shuttle, I was sold, in theory. I just had to wait for a pair to be created that was within my budget and a good size for traveling.

As I finally found myself a reasonably compact pair in a price worth testing, I thought I’d find SciAm readers a video explaining the science and technology of active noise canceling headphones work, and surprisingly found ONLY one. It comes from James May at HeadSqueeze. I think it does a fairly good job at explaining the technology, even if he completely forgets to use the term ‘destructive interference’!

And in case you want a little more visual science, I found this brief but effective demonstration on the fundamentals of sound wave interference, both constructive and destructive.

There are several websites that explain how these headphones work, so a simple google search will lead you to them, but really, Wikipedia does a fine job if you don’t mind a bit of physics terminology.

Sound is a pressure wave, which consists of a compression phase and a rarefaction phase. A noise-cancellation speaker emits a sound wave with the same amplitude but with inverted phase (also known as antiphase) to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out – an effect which is called phase cancellation.

Modern active noise control is generally achieved through the use of analog circuits or digital signal processing. Adaptive algorithms are designed to analyze the waveform of the background aural or nonaural noise, then based on the specific algorithm generate a signal that will either phase shift or invert the polarity of the original signal. This inverted signal (in antiphase) is then amplified and a transducer creates a sound wave directly proportional to the amplitude of the original waveform, creating destructive interference. This effectively reduces the volume of the perceivable noise.

A noise-cancellation speaker may be co-located with the sound source to be attenuated. In this case it must have the same audio power level as the source of the unwanted sound. Alternatively, the transducer emitting the cancellation signal may be located at the location where sound attenuation is wanted (e.g. the user’s ear). This requires a much lower power level for cancellation but is effective only for a single user. Noise cancellation at other locations is more difficult as the three dimensional wavefronts of the unwanted sound and the cancellation signal could match and create alternating zones of constructive and destructive interference, reducing noise in some spots while doubling noise in others. In small enclosed spaces (e.g. the passenger compartment of a car) global noise reduction can be achieved via multiple speakers and feedback microphones, and measurement of the modal responses of the enclosure.

Ultimately, I made my decision based on CNET reviews In addition, I found a recent review/explanation over at Forbes. Are Noise-Canceling Headphones Worth It?

Ultimately, I chose this pair, at least for now.

Do you have a pair you love (or hate)?

Joanne Manaster About the Author: Joanne Manaster is a university level cell and molecular biology lecturer with an insatiable passion for science outreach to all ages. Enjoy her quirky videos at www.joannelovesscience.com, on twitter @sciencegoddess and on her Facebook page at JoanneLovesScience Follow on Twitter @sciencegoddess.

The views expressed are those of the author and are not necessarily those of Scientific American.





Rights & Permissions

Comments 4 Comments

Add Comment
  1. 1. Halbred 6:00 pm 02/24/2014

    My mother swears by her’s–she uses it on airplane flights constantly (I forget the brand). She recommended I take them to “Walking with Dinosaurs 3D,” as my stomach churned at the thought of enduring the chatty voiceovers. I am sad to say they didn’t really work as advertised in a movie theater: the sound was muffled, but definitely present. I could even hear people talking around me.

    Perhaps they are good at canceling out chronic background noise, but certainly not speech.

    Link to this
  2. 2. porthome 9:58 am 02/28/2014

    I recall a short story by Arthur C Clarke published sometime back in the fifties about an invention to cancel out noise by broadcasting the inverse of the sound. I think it was used by an evil dictator to silence a protesting mob by soaking up their shouts, resulting in silence. The punchline was that although the sound waves destructively interfered, the energy being transmitted was cumulative, and so after a while everything blew up. Isn’t this still the case?

    Link to this
  3. 3. JoshYoung 6:04 am 04/24/2014

    I have also done an in depth research on various noise cancelling headphones and have reviewed many of them as a part of this process. All of my reviews are posted on http://www.headyo.com which is a definitive guide to the in depth reviews and ratings for all the noise cancelling headphones.

    Link to this
  4. 4. IrenaDuran 12:57 pm 09/9/2014

    While I can appreciate the value of noise-cancelling headphones in certain circumstances I lean more toward the use of acoustic filters so that I can remain aware of my surroundings without experiencing the harm caused by noise pollution.

    A product that “changes the way we hear the world” is something I’d like to learn more about: http://techcrunch.com/2014/08/26/dwnld-doppler/

    Link to this

Add a Comment
You must sign in or register as a ScientificAmerican.com member to submit a comment.

More from Scientific American

Scientific American Holiday Sale

Limited Time Only!

Get 50% off Digital Gifts

Hurry sale ends 12/31 >

X

Email this Article

X