Noise-cancelling headphones are a special type of headphones which suppress unwanted ambient sounds using active noise control. This is distinct from passive headphones which, if they reduce ambient sounds at all, use techniques such as soundproofing.
Noise cancellation makes it possible to listen to audio content without raising the volume excessively. In the aviation environment, noise-cancelling headphones increase the signal-to-noise ratio significantly more than passive noise attenuating headphones or no headphones, making hearing important information such as safety announcements easier.[1]
Theory
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Simplified graphical depiction of active noise reductionTo cancel the lower-frequency portions of the noise, noise-cancelling headphones use active noise control or ANC. A microphone captures the targeted ambient sounds, and a small amplifier generates sound waves that are exactly out of phase with the undesired sounds. When the sound pressure of the noise wave is high, the cancelling wave is low (and vice versa). The opposite sound waves collide and are eliminated or "cancelled" (destructive interference). Most noise-cancelling headsets in the consumer market generate the noise-cancelling waveform in real time with analogue technology. In contrast, other active noise and vibration control products use soft real-time digital processing. According to an experiment conducted to test how lightweight earphones reduced noise as compared to commercial headphones and earphones, lightweight headphones achieved better noise reduction than normal headphones. The experiment also supported that in-ear headphones worked better at reducing noise than outer-ear headphones.[2]
Cancellation focuses on constant droning sounds like road noise and is less effective on short/sharp sounds like voices or breaking glass. It also is ineffective in eliminating higher frequency noises like the sound of spraying. Noise-cancelling headphones often combine sound isolation with ANC to maximize the sound reduction across the frequency spectrum. Noise cancellation can also be used without sound isolation to make wanted sounds (such as voices) easier to hear. Noise cancellation to eliminate ambient noise is never passive because of the circuitry required, so references to passive noise cancellation actually are referring to products featuring sound isolation.
To prevent higher-frequency noise from reaching the ear, most noise-cancelling headphones depend on sound isolation or soundproofing. Higher-frequency sound has a shorter wavelength, and cancelling this sound would require locating devices to detect and counteract it closer to the listener's eardrum than is currently technically feasible or would require digital algorithms that would complicate the headphone's electronics.[3]
Noise-cancelling headphones specify the amount of noise they can cancel in terms of decibels. This number may be useful for comparing products but does not tell the whole story, as it does not specify noise reduction at various frequencies.
In aviation
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By the 1950s, Dr. Lawrence Jerome Fogel created systems and submitted patents regarding active noise cancellation in the field of aviation. This system was designed to reduce noise for the pilots in the cockpit area and help make their communication easier and protect hearing. Fogel is considered to be the inventor of active noise cancellation, and he designed one of the first noise-cancelling headphones systems. Later on, Willard Meeker designed an active noise control model that was applied to circumaural earmuffs for advanced hearing protection.
In 1989, Bose Corporation introduced its "Series I Aviation Headset" which became the first commercially available ANR headset. It included a noise-cancelling function and was powered either by NiCad batteries (with a claimed battery life of 8 hours) or by power from the aircraft. Series I aviation headsets are distinguished by the clear windows on the earcups or by noting that the on/off switch and volume control are located on the separate control module.[4]
Several airlines provide noise-cancelling headphones in their business and first-class cabins. Bose started supplying American Airlines with noise-cancelling headphones in 1999 and started offering the "Quiet Comfort" line for the general consumer in 2000. Noise cancelling is particularly effective against aircraft engine noise.[citation needed] The electronics, located in the plane hand rest, take the sound from the microphone behind the headphone, invert it, and add it back into the audio signal, which reduces background noise.[4]
As a sleeping aid
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Noise-cancellation headphones have been used as sleeping aids as well.[5] Both passive isolating and active noise-cancellation headphones or earplugs help to achieve a reduction of ambient sounds, which is particularly helpful for people suffering from insomnia or other sleeping disorders, for whom sounds such as cars honking and snoring impact their ability to sleep. For that reason, noise-cancelling sleep headphones and ear plugs are designed to cater to this segment of patients.[6]
In hospitals
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The use of noise-cancelling headphones for patients in intensive care units has been implemented to reduce the amount of noise exposure that they face while in a hospital environment. Active noise control technology is shown to have a relationship with sleep disturbance, delirium, and morbidity, therefore bringing up concerns about lowering the levels of noise for patients receiving care.[7]
Health and safety
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There is a general danger that listening to loud music in headphones can distract the listener and lead to injury and accidents.[8][9] Noise-cancelling headphones add extra risk. Several countries and states have made it illegal to wear headphones while driving or cycling.[10]
It is not uncommon to get a pressure-like feeling when using noise-cancelling headphones initially. This is caused by the lack of low-frequency sounds as being perceived as a pressure differential between the inner and outer ear.[11][12][13]
Autism
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A December 2016 study from the Hong Kong Journal of Occupational Therapy found that noise-cancellation headphones helped children with autism spectrum disorder cope with behaviors related to hyper-reactivity and auditory stimuli.[14]
Drawbacks
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The active noise control requires power, usually supplied by a USB port or a battery that must occasionally be replaced or recharged. Without power, some models do not function as regular headphones. Any battery and additional electronics may increase the size and weight of the headphones compared to regular headphones. The noise-cancelling circuitry may reduce audio quality and add high-frequency hiss, although reducing the noise may result in higher perceived audio quality.[15]
The biggest issue with Active Noise Cancelling (ANC) is sampling ambient sounds accurately enough to provide the maximum degree of attenuation. Microphones must capture the noise, and the phase of the cancellation waveform leaving the headphone drivers needs to perfectly line up with the phase of the noise when it reaches your ear.
See also
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References
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Noise cancelling headphones are as popular as ever, but have we really asked ourselves where did all this hype come from? Let’s take a moment and go back in time to discover the geniuses behind this innovative noise cancellation idea.
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Brace yourself, I’m gonna talk history to you now.
It all started in Germany in 1933 when Paul Lueg, a doctor of philosophy and medicine, submitted a patent application about using phase-advancing waves to cancel sinusoidal tones in ducts and inverting polarity to cancel sounds around a loudspeaker.
Sounds complicated, but actually the process incorporated displacing the phases with the source of sound oscillations (i.e. in simpler terms vibration of air particles parallel to the direction of wave) in a way that their superposition (i.e. superposition property, according to which net response by two or more stimuli in the response sum is caused by each stimulus individually for all linear systems) is in mechanical manner.
Let’s stop with the science here and continue with the patent, which was granted in 1936. It was theoretically functional, however there wasn’t any proper equipment to detect, process and generate sound. Paul Lueg couldn’t implement this to a further phase.
Later in 1950s, Dr. Lawrence Jerome Fogel took over and he was one of the pioneers in evolutionary computation and human factors analysis research. Fogel developed systems and submitted patents on active noise cancellation in the field of aviation (helicopters to be exact).
This system was designed to reduce noise for the pilot in the cockpit area and help make the communication easier. Fogel was considered to be the inventor of active noise cancellation and he created one of the first noise cancelling headphones systems.
Around the same time the Air Force Research Laboratory (AFRL) had an acoustics research program that was focusing on hearing conservation and protection, communicating speech, measuring noise and community noise modeling. While working on active and passive hearing protection technologies, AFRL also had an ANR headset project in between 1956 and 1957.
Willard Meeker was the leader of the project and introduced the concept of earmuffs and earplugs as passive hearing protectors which was later developed by Dr. Charles Nixon. These passive hearing protectors were enhanced with Meeker’s newly designed active noise control model.
The circumaural earmuffs had 50-500 Hz bandwidth and 20 dB maximum attenuation. This was a breakthrough invention for noise cancelling headphones at the time which laid a ground for further developments.
Here comes the most prominent part in the story of noise cancelling headphones
Fastforwarding to 1978, a sound engineer and the founder of Bose Corporation Dr. Amar Bose first thought about reducing noise in headphones during his flight to Europe.
Listening to music and relaxing wasn’t an option for him because of airplane engine noise, so he dedicated his time to the concept of building noise cancelling headphones that started right in that plane.
By the time his trip was over, he gathered together a whole research team for building the noise reduction technology.
The end result was that BOSE came up with a whole new working prototype of acoustic noise cancelling headphones. This buddy was enhanced with a built-in microphone in each earmuff, which detect the external sound sooner than it reaches the human ears.
Then, noise-canceling circuitry (which is also in the earmuff) detects the microphone input and measures the frequency and amplitude of the soundwave to create an opposing soundwave.
Later the two sound waves are combined together along with destructive interference signal and the anti-sound removes the noise without affecting the normal sound.
This was the ultimate time when Bose headphones passed a real test in 1986 by Dick Rutan and Jeana Yeager. They flew a two-seater plane (known as Rutan Model 76 Voyager) for 9 days, 3 minutes and 44 seconds which set a new flight endurance record. Imagine how difficult would it be to fly in the air for that long without noise cancelling headphones!
Either way, Bose wasn’t the only headphone producing company to work on noise cancelling headphones. Another major Germany-based headphone producing company called Sennheiser worked on active noise reduction in headphones.
They were designed to help pilots of the largest German airline Lufthansa protect themselves from low-frequency noises. They presented the first certified (FAA-TSO) active noise cancelling pilot headset by the name of LHM 45 NoiseGard in 1987.
From then on, noise cancelling headphones gained fame and caught the eye of many headphone and other audio equipment producing companies. People started using them not only in aviation but in their daily routine as well since they’re completely safe for ears.
Noise cancelling headphones are also quite widely used by business folks to have better conference calls.
The market has become fairly competitive, and if you’re also in search of the best noise cancelling headphones, we got your back! By the way, they do not have a negative impact on your hearing.
In case you are interested in noise cancellation, we have designed an AI noise reduction app called Krisp that will remove noise in your conference calls.
The technology works in a way that will help you cancel both your noise and the noise coming from the other call participants. Now that’s something noise cancelling headphones wouldn’t be able to do, so get it while you can. 😉
Let’s see how this never-ending story of noise cancelling headphones will change in 2019 and where it will take us!