How Does Noise Cancelling Work?

Got a pair of noise cancelling headphones and wondered just how exactly they work? Let us break down the concepts behind one of the best breakthroughs in headphone technology.
Noise
  • Cancelling Noise
  • Microphones
  • Noise Cancellation Types
  • Can Noise cancelling headphones cause dizziness?
  • Noise

    To understand how noise cancelling headphones work, first you need to understand what noise is. 

    In any scientific diagram of noise or sound, you see it depicted as a wave, as pictured. In reality this is the compression and decompression of particles in the air (or any medium really – but for our purposes here we will be talking about air). The moving particles lead to changes in air pressure which your ears and brain pick up and determine as the sound you hear. You can see that the sound wave is made up of two “parts”; its amplitude and wavelength. Amplitude is the measured power in the changes in air pressure which changes the loudness of the sound i.e. the bigger the amplitude the louder the volume. The wavelength determines the pitch with which you hear the sound i.e. smaller wavelength = a higher pitch and vice versa. 

    Cancelling Noise

    So how do headphones cancel out these sound waves? The short answer: with tiny microphones that listen to the outside noise and quickly create an inverse sound wave of the external noise. 

    Noise cancelling headphones do their best to employ a nifty physics trick called anti-phase to negate the noise from the outside world.

    If you take 2 soundwaves of the same amplitude and wavelength and match up their peaks and troughs, the two waves are “constructive” or in-phase. This means that the soundwave will combine to create a greater amplitude, or a louder noise. 

    If you reverse this, and align the peak of one soundwave to the trough of another, they are said to be “destructive” or in anti-phase. In this scenario, the peak of one soundwave is negated by the trough of the other, and you get no wave, as seen in the diagram.

    Microphones

    So how exactly does your noise cancelling headphones make use of this physics trick?

    Noise cancelling headphones will have tiy microphones on the outside of your headphones listening to the noise around you. The onboard electronics in your headphones will then use this information to create the inverse sound wave (to employ this anti-phase trick), which cancels out the outside noise – leaving just you and your music in peace. This is called active noise cancelling, or ANC.

    In practice of course this is very hard to achieve. It’s much easier to cancel out the constant hum of a plane engine than it is to recognise and cancel out sudden random noises, like a dog barking. And because of this, some companies are better at it than others, and you need to find the right pair for you. 

    Noise Cancellation Types

    You may see headphones advertise different types of noise cancelling. Here is a brief summary of what each type/mode means:

    Passive Noise Cancellation:

    This is a physical feature of the headphones which will help block out some noise. This will employ well designed over hear cups on the headphones to reduce the amount of surrounding noise that you hear. 

    Active Noise Cancellation:

    This is what we have primarily gone through in this article, and is the most well known type of noise cancelling type. This uses microphones and speakers to negate the noise from the outside world. 

    Adaptive Active Noise Cancellation:

    Adaptive noise cancelling uses the same methodology as ANC, but is more sophisticated to be more adaptable to those sudden noise changes we were speaking about earlier. 

    Adjustable Active Noise Cancellation:

    Adjustable ANC allows the user to control how much outside noise you want to hear, rather than just being “on” or “off”.

    Transparency Mode:

    This is a mode you can find on some headphones to enable some background noise to be heard. This can be pretty useful when you’re walking around a city and need to hear things like traffic etc.

    Adjustable Transparency Mode:

    This allows you to adjust the amount of background noise you want to hear – very similar to Adjustable ANC.

    Can Noise Cancelling Headphones cause Dizziness?

    It has been reported that noise cancelling headphones can cause dizziness and disorientation. According to ear, nose, and throat doctor in the Wall Street Journal, Sarah Stackpole; noise cancelling technology may transmit low frequency vibrations to our ears’ stereocilia. This may lead to the receptors to falsely communicate to the brain that the head is moving when it is not, leading to the feeling of dizziness.

    One solution to this, for those moderately affected by this, is to decrease the intensity of the ANC being employed by the headphone’s if you have an adjustable ANC. Otherwise, you can opt for a Passive Noise Cancellation headphones. 

    So now you can enjoy your noise cancelling headphones with full peace of mind around just how exactly they work. Remember, turning noise cancelling on will consume more battery power on your headphones; although the technology and efficiency of ANC is constantly improving. So you can enjoy your chosen soundscape in peace. 

    “Music is the language of the spirit. It opens the secret of life bringing peace, abolishing strife.” ― Kahlil Gibran

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