Photos:
Top: Active Noise cancelling headphones  cut out unwanted outside noise. Photo Credit: Sony
Bottom: Dr Amar Bose  and the principle of active noise cancellation
By Anand Parthasarathy
April 16, 2023: Let me begin with a personal anecdote:  I live in an apartment complex where the biggest dread is that an adjacent flat should not change hands. This usually means  a new occupant – and  a week or two of incessant hammering, drilling, grinding to redo the  place —all very noisy. 
But I have a small solace: I dig out my prized possession – a vintage pair of ‘Quiet Comfort’ headphones crafted by Bose Corporation, US— arguably the world’s most respected  brand for good audio quality.   The pair in question has sentimental value for me in addition to its utility:   It was the world’s first consumer headphones with built-in active noise cancellation.  And it was  presented to me (and to five other visiting Indian journalists) by Dr Amar Bose when we visited the hill-top global headquarters of Bose Corp., in Framingham, just outside Boston, Massachusetts (US), during a media event in 2005.  
I realised quite soon that one does not have to use noise cancelling earphones just to enhance the music experience. One can use them just to reduce,  if not eliminate, the level of outside noise.
The idea of cutting out outside or ambient noise from headphones tuned to music, occurred to Dr Bose, then a professor of Electrical Engineering at the Massachusetts Institute of Technology (MIT) in 1978, while taking a long flight to Europe. He found that the incessant noise and vibration of the aircraft engine added to the air-conditioning in the cabin, seeped through the headsets provided and spoiled his enjoyment of the music.  This set his mind working – how to cut out the unwanted external noise.
The principle was known from the 1950s and indeed, is attributed to the American engineer, Dr Lawrence Jerome Fogel. But it was Bose and his team at the company he had founded in 1964,  that translated the theory into a product. The theory went like this:
Fighting noise with anti-noise
If sound waves carrying unwanted sound (ie, noise) hit the headset, cancel them by creating sound waves that are equal and opposite in polarity and thus cancel the net sound to zero.  In other words, fight noise with anti-noise. The principle is known as ‘destructive interference’
This is done by embedding the headphones with tiny microphones – and a processor that takes the unwanted sound received by the microphone and ‘cancels’ it electronically. This leaves the wearer free to clearly receive the sound he or she wants to hear:  music, TV, movies, whatever.  The electronics mostly work on the lower end of the audible frequency band which ranges from around 20 Hz to 20 Khz, so continuous background sound like street noise is cut off. But it is less effective in handling sharp, shrill sounds – so a siren, a car horn or a hammer in use, may get through. This remains true even today
Dr Bose  found  a ready  market in the commercial aviation industry,  which soon  equipped pilots with Bose noise cancelling phones to cut out the intense noise in the cockpit.
It took another 14 years before the Bose Corp launched the first consumer version of its active noise cancelling headphones, called Quiet Comfort, in 2000 – and since then lay users have been able to listen to what pleased them, while cutting out the cacophony around them- -- on flights, in busy public areas – or like me when the neighbours start civil construction. The technology of fighting noise with noise is called Active Noise Cancellation. It requires the headset to have special circuits built into it with a battery to power them, which has made such equipment rather heavy to wear – till now.
In view of the loose use of the term noise cancellation  by many products, it is necessary to distinguish active noise cancellation from passive noise cancellation. The latter has no special circuits and uses things like soft cushioning or rubber-like cups to surround the ear and muffle the unwanted outside noises.
 It is nearly two decades since my vintage pair of wired Bose Quiet Comfort headphones were made – and I could recently appreciate how leading audio electronics companies like Blaupunkt and Sennheiser in Germany, Beats in the US and Sony in Japan, have refined and improved active noise cancelling audio technology, in recent years.
Made-in-India brands like BoAt too, have helped bring down the price of noise cancelling technology in audio devices.  Bose itself, whose latest in the on-ear noise cancelling range is Quiet Comfort 45, introduced the technology to in-ear phones in 2020 and called them Quiet Comfort Earbuds. Now, many others have done likewise.
A longer version of this article which includes the review of a recently launched active noise cancelling phone from Sony, appeared yesterday on the Swarajyamag site.
The review  of Sony's  WH-CH720N headphones can be found in our Product Pulse section