Noise cancelling headphones make it possible for people to listen to audio content without having to raise the volume excessively. The special headphones can totally offset the effects of a distracting noise, enabling the wearer to relax in a noisy environment, such as when they’re travelling on an aircraft, for example.
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Who invented the headphones?
Dr Lawrence Jerome Fogel, an American pioneer of electrical and aerospace engineering, is credited with inventing the concept of noise-cancelling headphones in the 1950s. The Brooklyn-born inventor submitted a patent about using noise cancellation in the field of aviation. He designed a system to protect pilots’ hearing in the cockpit area. His noise-cancelling headphones are believed to be the first.
Later, between 1956 and 1957, the Air Force Research Laboratory developed the idea further, led by Willard Meeker, who introduced earplugs and earmuffs as passive hearing protectors, further enhancing them with his new active noise control design. The concept of noise cancelling headphones advanced quickly in the 1970s, thanks to Dr Amar Bose, the founder of Bose Corporation.
The sound engineer was on a flight to Switzerland from the USA in 1978 when he put on the headphones provided by the airline to listen to music during the flight. However, he realised the continual drone of the engines meant he couldn’t enjoy the music, as he could hardly hear it.
Belief has it that he grabbed a paper napkin and began scribbling down mathematical calculations to see if it was feasible to design headphones that would reduce the external noise. As soon as he arrived back from his European trip, Dr Bose formed the Noise Reduction Technology Group and began working in earnest on his new design.
When were they commercially available?
In 1986, Dr Bose’s design had its first real test, when pilots Dick Rutan and Jeana Yeager took off in their two-seater Rutan Voyager plane from the desert in South Carolina to set a new flight endurance record of nine days, three minutes and 44 seconds.
Both pilots wore the prototype noise cancelling headphones designed by the Noise Reduction Technology Group to protect their ears during the gruelling flight. The headphones passed the test with flying colours and this led to Dr Bose making them commercially available for the first time in 1989.
At the same time, the German headphone production company Sennheiser was also working on noise reduction technology to assist pilots on the nation’s largest airline, Lufthansa. Sennheiser was developing its LHM 45 NoiseGard as a pilot headset by the late 1980s.
Numerous airlines began to offer noise-cancelling headphones in their business and first class areas, as the technology proved most effective against the engine noise. The special headphones were around the same size as an ordinary headset, with their electronics located in the seat’s hand-rest.
Over the years, continual technical developments have enhanced the noise cancelling headphones, so that today, they will block almost three-quarters of the noise in an aircraft cabin.
How do the headphones work?
Active noise control technology in the headphones cancels the lower frequencies of exterior sounds. First, a microphone measures the ambient sounds. This generates a waveform that is an exact negative of the ambient sound. It then mixes it with any audio signal that the listener prefers.
The higher-frequency noises are prevented from reaching the ear by soundproofing. They have a shorter wavelength, so in order to cancel them, the headphones would require devices to counteract them closer to the user’s eardrum. Currently, this isn’t technically feasible, as it would mean using more complex digital algorithms.
The headphones come in passive or active varieties. With passive headphones, the materials block out some sound waves – in particular those of higher frequencies. The most effective passive noise-cancelling headphones are known as circumaural, which means they fully cover the outer part of the ear.
Manufactured using layers of a sound-absorbing material, such as high-density foam, they are heavier than normal headphones and create a noise reduction of around 15 to 20 decibels. This means the passive headphones aren’t best suited for use in the airplane cabin, where the engines can create noise of between 75 and 80 dB.
This is where active noise-cancelling headphones have the advantage. They do everything the passive ones can do and more besides. Their design creates a barrier to block high-frequency sound waves. In addition, they add an extra level of noise reduction by actively blocking low-frequency sound waves.
They do this by creating their own sound waves to mimic the incoming noise. The two waves (the one emitted by the headphones and the one coming from the external ambient noise) effectively cancel each other out. This phenomenon known as “destructive interference” enables the user to focus on the sounds they wish to hear.
Do the headphones block every loud noise?
The active headphones provide an additional reduction in noise of around 20 decibels. This means they can effectively block some 70% of ambient noise, making them ideal for airline travel, train travel, open-plan offices and any other location which suffers from a high level of background noise. Although they can’t block literally every loud noise, they are more than adequate for most people’s needs in average day-to-day situations.
As experienced acoustic consultants, Sound Planning provides a wide range of products and services to help protect people from noise nuisance. We specialise in the design, supply and installation of noise control products.
For more information about our bespoke solutions, please contact us.