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The sound of silence: how noise cancelling headphones actually work

Noise Cancelling Headphones

If you’ve been following our posts as of late, you know that we’ve been paying homage to the importance of ear health. It’s so easy to crank up the volume to better hear your favourite playlist or podcast over the sounds of the city traffic or your morning train commute. And you would be kidding yourself if you think that the deep roars of a jet plane engine isn’t going to affect the intelligibility of your tunes or fatigue your hearing

So let’s take a closer look at the recent advent of noise cancelling headphones. The tale behind this technology – which we take for granted these days – is worthy of exploration. Noise Cancelling Headphones

What started out as an aviation tool in the late ’70s has become somewhat of a survival tool in modern times. Let’s explore how noise cancelling headphones have changed the way we hear.

Poise in the Noise

Sound engineer and the founder of BOSE Corporation, Dr. Amar Bose first thought about reducing noise in headphones during a flight to Europe. Aeroplanes are a classic example of unwanted and uncomfortable noise pollution. Jet engines create up to 80dB of noise inside the cabin alone. 

Listening to music and relaxing wasn’t an option for him because of the immense aeroplane engine noise, so he dedicated his time to conceptualise a way for headphones to interact with a user’s surroundings.

Bose designed a system that would use a microphone inside the headphones to pick up all the noise occurring in the atmosphere around the user. That noise would then be sent to electronics that generated an equal and opposite signal within a fraction of a millisecond that cancelled out the sound before it reached the eardrum of the listener. That was his theory, at least.

When he returned to his office in Boston, Bose formed a team of engineers to work on his design. It took over 15 years before they were able to make the concept work and even people within the company were sceptical about the concept.  

Fast forward to 1989, BOSE was able to produce the first commercially available noise cancelling headphones aimed specifically for pilots, the BOSE Aviation Headset. It allowed pilots to better hear audio and communications over the roaring engine noise. 

This technology was then brought to ground level and was commissioned by the NFL for coaches to better interact with their assistant and players to make faster and more effective decisions on the field over the dynamic sounds of the stadium’s ambience. 

This revolutionary invention soon hit the consumer market and has kept somewhat of the same technology and design features from the original blueprints. The rapid innovation of digital technology has allowed for active noise cancelling to become cheaper, more adaptable and more user-friendly, however, with the addition of better microphones, smaller batteries, a more comfortable fit and sleeker designs. 

How does Active Noise Cancelling Technology Actually Work?

If you’re familiar with sound engineering and studio recordings, phase cancellation is often one of the things that you’re actively avoiding. 

Phase cancellation, otherwise known as destructive-interference, occurs when the wave on one signal is in its peak and the other is simultaneously in a trough. Because the peaks and valleys are out of sync, they work against each other rather than supporting each other. 

The frequencies are cancelled out and, acoustically, it causes a weak sound. This occurrence is every recording engineer’s nightmare and is always avoided. However, this often unwanted occurrence is exactly how active noise cancelling (ANC) technology operates!  

These headphones work via tiny microphones in the ear cup. They receive the outside sound before it hits your ears. Noise cancelling circuits note the frequency and amplitude of the sound and creates an anti-sound. This opposing frequency is mixed with the original sound and fed to the headphones speakers.

The Safety Issue

Ear safety is an important venture and ANC technology has done a lot to improve this as listeners can enjoy their favourite tunes at lower volumes.

Although this improves listening intelligibility with blocking out ‘noise’, active noise-cancelling technology has yet to fully realise the ability to completely cancel speech. Current active noise cancelling technology works best for frequencies below 500 Hz and is somewhat effective only up to about 1000 Hz.

Engine noise and traffic rumble are mostly below 500 Hz and so are greatly reduced or even completely eliminated through ANC. The important frequency range for understanding human speech, however, only starts at around 500 Hz. The most important bands for speech intelligibility are 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz.

With current top-of-the-line noise cancelling headphones, you can expect between 15 and 25 dB noise reduction from 500 to 2000 Hz, which is substantial but not nearly enough to eliminate speech.

The ear cups’ seal and isolation substantially attenuates voices and other higher-pitched noise. For speech blocking, active noise cancelling headphones rely mostly on passive sound isolation, not on their electronics.

Bringing it to the Wider Public

Although Amar Bose’s original ANC vision still reigns supreme, there has been a recent emergence of noise cancelling earbuds as opposed to headphones.

While still retaining the same technology, the infatuation of ANC earbuds brings the technology to the wider public – more accessible for your average consumer and perhaps preferred for commuters. This could be due to their small design, light weight and non-intrusive nature. 

Although BOSE first brought the over-ear technology to consumers, SONY was the first to bring ANC technology to the earbuds format. However, late in 2019 the monolithic tech company Apple released their own version with the Airpod Pro. This was perhaps the first time that the wider-public became aware of ANC technology due to the company’s reach.

Summing up this Noise

Noise-cancellation technology has come far from being introduced as a means for easier pilot communication to being a staple accessory for daily commuters. However, this technology can be applied to more than you may think.

ANC still functions without the need to listen to anything. This means you can use them as a kind of super-earmuff if you’re after peace and quiet more-so than hearing your favourite tunes with more clarity and less noise.

The technology has also been suggested by medical practitioners to patients who suffer from sleep disorders such as insomnia. Just by turning on the active mode on your ANC headphones, you’ll find the technology working to minimise the sounds of the cars outside or your parter’s snoring!

More so than anything else, they are an active contributor to ear safety by reducing loud levels of noise pollution and minimising ear fatigue.

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January 24, 2020