Noise Cancellation

Noise Cancellation – All You Require To Know About It!

Today, almost all have heard ‘Noise Cancellation’. But very few know the mechanics behind it. So, in this post, we will see how actually does this process happen. First, why this post? As I discuss regularly the various technical stuff that is related to gadgets like headphones, Fitness Trackers, etc.

So, I found this a very important topic to put forward has what you are going to learn ahead is a good piece of information.

Some Useful Resources.

I have taken care to keep this post very simple with no heavy equations. But you can check out the resources for the technical part of it. Therefore, anyone even amateurs can understand the concept easily.

So, let’s begin the topic.

Why Do We Need Noise Cancellation?

 

sound wave noise

 

In today’s busy environment one can hear Noise even at a very silent place. Yes, that much noise is there interfering us and our music. Recall the situation when you were listening to music and sadly were not able to listen to it properly. How did you feel at that time?

Bad, I know but for eradicating such a problem NC technology is used. Moreover, Noise cancellation not only reduces the penetration of large frequencies but also of small frequencies.

Types Of Noise Cancellation?

There are two types of Noise Cancellation techniques that you will find in headphones and earphones namely-

  • Passive Noise Cancellation
  • Active Noise Cancellation

We will talk about both the types in detail in this post. But, just a small spoiler, Active Noise Cancellation has better noise resistance than Passive Noise Cancellation.

The Concept Of Noise Cancellation

 

noise cancellation

 

Until now we learned why we need noise cancellation and how many types of Noise Cancellation exists. Don’t worry in the further section we will discuss the individual types. But before that let’s see what noise cancellation is as a concept. As the name indicates, it has the property of eradicating unwanted sound, which we call noise before it enters the ear.

Moreover, this operation is carried out both physically and with the help of specialized electronic circuits.

Passive Noise Cancellation [Assume PNC]

The first and the most basic design for canceling noise is applied in the passive method. In PNC, noise is prevented from entering the ears with the help of physical means. In Order to achieve this, the manufacturers design the earcups to have a closed structure with a more quantity and better quality of ear foams.

These foams cover the ear tightly. Moreover, they also have some sound absorbing properties which prevents noise from entering your ears. Furthermore, such earphones and headphones are in-ears and closed back. You don’t get any Noise Cancellation feature in the Open Back category of headphones.

Now, what are the factors required for a material to block the passage of noise?

There are three major degrees of freedom, they are listed below –

  • Mass
  • Absorption (foam, sponge, rubber, etc)
  • Stiffness

Degrees Of Freedom

 

These three materials can be used to achieve noise cancellation passively. From the 3 degrees of freedom, the one that we observe in our headphones is the mixture of these three.

The earcups outer surface which is made up of hard material, the ear foams and the junction of these two. Therefore, such a design can help us to enjoy music free from a large portion of the noise.

Active Noise Cancellation [ANC]

  • After understanding the power of passive ANC you might be thinking, what is the use of NC of passive does the work so well. Your doubt is absolutely valid. Yes, passive noise cancellation[PNC] is more than enough for many of us. It can handle situations like street noise, indoor noise, etc. But this too depends on how good PNC the headphone has. Not all headphones have excellent PNC.
  • If you travel a lot then you can correlate it with the noise generated by airplanes. The engines produce 75-80 dB of noise inside the plane. Moreover, good PNC headphones reduce the noise by 15-20 dB. Still, a lot of noise goes into your ears which irritates a lot. Here ANC benefits a lot. This is the reason you find many wireless headphones with long hours of battery life have good ANC feature.
  • ANC headphones have both passive and active. They make use of a special electronic circuit for this purpose. We will talk about this in detail in the next section. Also, there can be technically no comparison between Active and Passive NC because they both have different principles.

Basic Principle Of ANC

ANC is based on the principle of Superposition. Here care has to be taken so that the sound waves don’t add up to give a resultant having double the amplitude of the original wave. Therefore, a wave is generated which has a phase difference of 180 degrees or pie. On adding the waves, i.e. noise and generated wave we get a resultant which has no amplitude.

In such a way the noise is canceled. It seems to be easy but developing such circuits is challenging. Moreover, the accuracy of these circuits decides the level of ANC.

A very basic breadboard design to create an ANC system is given below. You can try this at home if interested.

 

Breadboard DesignImage source – Instructables

 

 

Image Source – m.eet

 

The above image is a great depiction of what happens during the process of ANC. As you can see the waves coming from outside [noise] reach the headphone. The mic built inside the headphone does the function of picking up the noise wave. This noise wave is treated with another wave generated by the speakers.

This wave is 180 degree out of phase with the noise wave. Both these waves are algebraically added which results in a wave with zero amplitude  [Note: In theory] This is so beautiful. Just imagine while you are listening to music all this happens continuously and we are unaware of this art.

If you are interested in learning and creating your own ANC system. Check out this very useful GitHub profile. Here he has all the required codes for this purpose.

Summing Up…

With this the post concludes, I hope you enjoyed this throughout. If you are an engineering student or an innovator, I would recommend you to check out the algorithm and the circuit design.

They will enhance your understanding of NC. If you liked this, please share it with your friends and family as they will love this too.

Thank you for reading this post.

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