Evolution of Active Noise Cancellation (ANC)
Table of Content
What is Noise Cancellation?
Everyone enjoys a little peace and quiet at some point or another, but given the society we live in, there's a slim chance we'll find it readily available. This is where noise-cancelling technology comes into play. As the name implies, it cancels out the ambient noise, making our world a little quieter. This technique was formerly only available in large, expensive headphones. Still, because of advances in the world of audio, it is now available in other headphones and wireless earbuds. This technology has grown in popularity to the point where almost every headphone or wireless earbud now has some form of noise cancelling. The technology took several decades to be developed and perfected before reaching the hands of the everyday consumer.
History of Noise Cancellation
The development of active noise cancellation technology may be traced back to 1933, when Paul Lueg, a German philosopher and physician, sought for a patent on his theory and detailed its foundations. This patent outlines how to phase advance a sinusoidal tone in a duct and reverse the polarity of any tone in the area around the speaker to cancel them both. It's the method of cancelling a sound wave by exposing it to the opposite sound wave through the use of a speaker and a microphone. This seemingly innocuous move paved the path for today's noise-cancelling headphones. Despite being patented and theoretically sound, the concept was far beyond advanced for the available technology at the time.
Dr. Lawrence Jerome Fogel applied for his own patents on noise cancelling in helicopters to protect the pilot's ears about 20 years after Lueg's patent was issued. Fogel was able to develop one of the first noise-cancelling headphones because to technological advancements. The device is designed to give active noise cancellation to helicopter pilots by lowering the overall noise felt by pilots in the cockpit area, allowing them to communicate more effectively. Even though these devices were designed primarily for aeroplane hearing protection, they set the groundwork for future advancements.
Willard Meeker created a realistic model of active noise control for earmuffs in 1957. This headset's active attenuation bandwidth was around 50-500 Hz, with a maximum attenuation of roughly 20 dB. Fogel pioneered noise cancelling headphones, but it was Dr. Amar Bose, the founder of Bose Corporation, who gave them their current design. Let's take a closer look at how today's technology inspires and encourages us.
Bose saw the first wave of innovative electronic headphones for in-flight entertainment during a travel from Zurich to Boston in 1978. The new headgear was incredibly light, weighing only 57 grammes. This is in comparison to the 453.5 grammes those previous model headphones and standard headsets weighed.
Bose was looking forward to using the new headset on the eight-hour flight from Zurich to Boston. However, he quickly learned that this was not possible because the plane's noise was so loud that he couldn't hear the music through his new headphones.
At this point, Bose's creative imagination and optimism in finding solutions to acoustic problems ignited the birth of innovative ideas. He knew that there must be a way around this particular problem.
So, he took off his headphones, picked up a piece of paper, and began sketching a design that would eventually be the first noise-cancelling headphones in history. The sketches he created on this flight became the main foundation and reference point for ground-breaking headphone design. When Bose finally returned to his Boston office, he brought together a group of engineers to work on the designs he had created. They had a working model in 1986, but it took more than a decade (about 15 years) for the concept to finally work as expected.
From making it easier for aviators to hear voice and communications with the Bose Aviation headset in 1989, to protecting the U. S. Army thanks to the 1993 Bose Combat Vehicle Crewman headset, Bose headphones have been a huge success over the years, and noise-cancelling headset technology is in the limelight.
How Does Noise Cancellation Work?
Having said that, it's important looking into how today's technology works. The concept of destructive interference is used by ANC (Active Noise Cancellation). The main premise is to use a microphone that cannot be passively cancelled to listen to noise from the outside environment. The noise signal is phase-shifted or inverted before being added to the original noise signal. The output signal removes noise without degrading the overall audio quality.
The ANC can be applied in the following topologies depending on the location of the microphone.
In feedforward settings, the microphone is located outside the ear cup. Mic hears noise before the user.
The microphone monitors external noise, and the active noise cancelling circuit converts it into "anti-noise" and mixes it with audio playback to create noise cancelling.
The microphone picks up noise early, so it has a longer time to react and generate back noise. It is also suitable for high frequency noise reduction. However, when generating a counter noise signal, you also need to consider the path covered by the actual noise signal. If the actual sound comes from a strange angle, the path through which the sound travels is slightly different, with a slight delay in reaching the user's eardrum. And anti-noise can't completely undo it. In some cases, if the path difference is greater, it actually amplifies the noise rather than cancelling it.
With this technique, the microphone is placed in front of the ear cups and speakers, so you can hear the resulting signal just as you would a user. Therefore, noise fluctuations can be easily inherited.
The feedback-type ANC is only effective in suppressing low-frequency noise because the round-trip time, including anti-noise monitoring, comparison, and generation, is longer than feedforward anti-noise.
Sometimes, a combination of both these topologies is used and termed as hybrid topology. Although we are using the best of both (feedforward and feedback) topologies, we are adding extra cost since we need to use two mics, one for outside and one for inside and along with the matching of these two, which leads to more costs.
Having seen how noise cancelling works, it is worth seeing some application areas. Few areas of application are -
For Consumer goods – Refrigerators, Washing Machines, lawn mowers, vacuum cleaners etc.
Aircraft and Cabin noise control
Public Phone Booths.
Noise reduction in HVAC systems especially air conditioners
Trucks and mining equipment
Naval ships and Pleasure Boats
Automobile Engine noise vibration elimination
And the most common one being used in headphones
These are some of the disadvantages of Active Noise Cancellation technology. The most crucial is that it is a little pricey. The noise cancellation circuit necessitates additional hardware, which is costly. Furthermore, because to the additional hardware, it increases total weight, but this can be rectified at an additional cost. The entire cost of employing ANC is determined by how much noise cancellation we want. The more noise we want to reduce, the more complicated and expensive the hardware becomes.
ANC technology has been quite an important advancement and quite useful considering the current situation wherein constant human presence and lack of private corners, at times, even in our homes, has made owning and using a pair of noise-cancelling headphones a necessity rather than a luxury.
Below is the industry trend regarding research in this field over the past 20 years with effect from 2002 until Jan 2022.
As we can see that the trend seems to drop over the last couple of years. A possible reason is the advent of new technologies which drew too much attention, leading to reduced funding in this area. Also, we see a list of the top 10 players working in this field of technology.
We can see that the majority of the companies are in the headphone industry, while the others are in some way related to consumer products. Cirrus Logic, Qualcomm, and BOSE are at the top of the list, as can be seen. As previously said in the essay, BOSE is a solely committed company in the headphone sector. Qualcomm has several products in this area as well. Cirrus Logic and Qualcomm are both audio and analogue signal processing semiconductor businesses. This demonstrates why they are the table toppers. Further, we see a graphical representation of the top 10 markets (in respect of the country) where the above-mentioned research trend is more focused.
We see that most of the research is in US and China, the research hubs of the world. Further, Europe is the third on the list owing to the technological advancements over there.
The ANC technology is on an impressive growth trajectory globally, with increased demand for premium audio coupled with higher purchasing power of the consumers. We expect to see ANC technology take a front seat in the future and a must have feature in the personal audio category.