In 1978, Dr Amar Bose was on a flight from Zurich to Boston. With the flight being eight hours long, Bose decided to try out a new pair of airline-supplied headphones. He found it impossible to enjoy the music, as the ambient noise in the cabin and the roar of the engine overpowered the sound of the music. Inspiration struck Bose, and, 15 years and fifty million dollars later, Bose Corporation released the first consumer-grade set of noise-cancelling headphones.

In the years that followed, the technology continued to evolve, with many other companies developing noise-cancelling headphones, such as Sony’s WH-1000XM4 and the Sennheiser HD 450BT. But how does this technology work? How did it develop?

How do they work?

These noise-cancelling headphones rely on a principle referred to as Active Noise Control, or ANC.

Sound, as we hear it, is the compression and rarefaction (or decompression) of particles in the air. These moving particles cause minute changes in the air pressure. Our ears and brain detect these changes and perceive them as sound.

Active Noise Control works by taking two identical waves, but shifting one to be half a wavelength out of phase with the other. A microphone, usually facing the outside of the headset, detects the ambient noises around the user. These noises are then fed into the active noise control chipset, which then calculates the necessary anti-noise to cancel out the sound.

For example, if there is a compression, the active noise control chipset and speaker would generate a rarefaction. This neutralises the ambient noises, as the positive pressures from one wave cancel out the negative pressures of the other (and vice versa) – a bit like adding one and a negative one.

Active Noise Control works best on low-frequency, droning sounds, such as air conditioning units or an aircraft engine, but is not as effective at faster, higher-frequency sounds, such as an alarm or a voice.

The history of Active Noise Control and noise-cancelling headphones

Active Noise Control was pioneered in 1936, by inventor Paul Lueg. Lueg patented the concept, but unfortunately, his concept was too advanced for the technology of the time. It wasn’t until 1958 that we saw a headphone system that incorporates Lueg’s concept. Dr Lawrence J. Fogel filed patents for his headphone system, which was designed to bring active noise cancellation to the cockpit. Fogel’s system aimed to reduce the noise pilots experiences, allowing for enhanced communication between pilots and air traffic control. This system was never made commercially available to average consumers, but it laid the groundwork for future developments.

The first set of commercially available noise-cancelling headphones was the Bose QuietComfort. As we mentioned earlier, they were designed for use in planes, to allow for in-flight entertainment systems to be more enjoyable for airplane passengers. However, from

customer feedback, Bose learned that their QuietComfort headphones worked in other noisy places, such as trains, buses, offices, and homes.

While Bose’s QuietComfort was the first consumer-grade noise-cancelling headphones, they were not the only company working on designing these products. The German audio company Sennheiser released the LHM 45 NoiseGard in 1987.

Development of the LHM 45 NoiseGard began in 1984, at the request of the German airline Lufthansa. It was the first pilot’s headset to receive FAA-TSO certification (Technical Standard Order of the Federal Aviation Administration).

Active Noise Control is not just applicable to headphones. The technology can, and has, been used in earbuds as well. Sony, in 1995, unveiled the MDR-NC10 earbuds. The MDR-NC10 incorporated active noise control, with a built-in microphone and noise-cancelling circuit working together to reduce outside noise by almost 70 percent. Sony even added a “Hot Line” switch, which temporarily disabled the active noise cancellation, allowing the listener to hear sounds around them if they so choose.

More recently, active noise cancellation has been brought over to wireless earbuds, such as Apple’s Airpods Pro (released in October 2019) and Samsung’s Galaxy Buds Live (released in August 2020). The Airpods Pro have two microphones – one facing the inside of the year,

and another facing the outside. This allows for the active noise cancellation chipset to generate a more accurate antinoise.

Noise-cancelling headphones and earbuds are not just used to listen to music. They have had many other applications, from aircraft cockpits and air traffic control towers to the battlefield and even space!

Prior to the 1990s, the US government paid out in excess of $200 million per year in compensation for hearing loss incurred as a result of military service. In 1993, Bose’s noise-cancelling headphones presented a solution to this major expense. The United States Army awarded Bose with a contract to supply Bose’s Acoustic Noise Cancelling headsets to crews of the M1A1 and M1A2 Abrams tanks.

The contract was a success, with crews reporting improved comfort, reduced fatigue, and clearer communications. This convinced the US Army to expand the contact a few years later, outfitting crews of several other vehicles with the headphones, such as the M2 and M3 Bradley and the M109A6 Howitzer.

Meanwhile, Sennheiser continued to develop their headphones, and, in 2000, their noise-cancelling headsets were put to use in space, by astronauts onboard the now-defunct Russian Mir space station.

Noise-cancelling headphones can also be used on construction sites. Studies have shown that noise cancellation is highly efficient in the low- and mid-frequency bands, below 1000 Hz. However, the reduction effect has been noted to decrease as the frequency of the ambient sounds increases.

Side effects of noise-cancelling headphones

While noise-cancelling headphones appear to be largely safe, there have been reports of side effects. The most common complaints include jaw pain, headaches, dizziness, and pressure on the ears. This has been attributed to the pressure changes caused as a direct result of how active noise cancellation works. Manufacturers are catching on to this, and development in recent years has focused on reducing the effects caused by pressure changes, primarily by distributing the pressure more evenly on the listener’s ears.

Another issue with noise-cancelling headphones is that, when used outside, the noise cancellation may make it difficult to hear sounds such as car horns, fire alarms, and sirens. This can put the listener and others around at risk. In fact, the US states of Colorado, Maryland, Louisiana, and Rhode Island have banned the use of headphones while driving, and other states strongly discourage it.

Companies such as Audio Analytic have begun developing artificial intelligence solutions to this issue, to allow users to hear sounds like car horns or sirens even when wearing noise-cancelling headphones.

Conclusion

Noise cancellation, when done well, can vastly improve the overall experience of the user. However, it is difficult to pull off, and has its limitations. Research and development continue, as companies strive to improve the quality of noise cancellation, and it is only a matter of time until the next breakthrough.