Article ID : 00256977 / Last Modified : 29/01/2021Print

Why do I hear sound with noise-cancelling on?

    Noise-cancelling can be the very reason you chose to buy headphones or earphones. You may want to cancel out noise on your daily commute, during a flight, or block out noisy neighbours. 

    Did you know?

    Sound can only travel if there is a medium to transport it, for e.g. air, water, glass or metal. If you stand in an empty room with a speaker playing music, you will hear the music. However, if the air from this room is removed for a few seconds, the speaker will still function, but you won’t hear any sound as there’s no medium to transport the sound waves. Similarly, Space is a vacuum — so it generally doesn’t carry sound waves like air does here on Earth (though some sounds do exist in outer space, we just can’t hear them)

    Why do I hear external sound when noise cancelling is on?

    Air trapped between your audio device and eardrum

    Noise-cancelling technology cannot completely isolate sound due to the air trapped between your audio device and eardrum. However, the air is important for you to be able to hear music. Suppose you were able to remove the trapped air, the net effect is silence, no matter what volume your music is on. Why? There would be no medium for the sound to travel from the audio device to your eardrum.

    Noise cancellation at different pitch levels

    Have you ever noticed how effective noise-cancelling is in cutting out the sound from an airplane engine? But when someone next to you speaks, you hear their voice. Why is that? 

     Sound waves from an airplane (Low pitch) 

     Sound waves when someone speaks (High-medium-low pitch) 

    How does noise cancellation work?

    Noise-cancelling audio devices use a built-in microphone to analyse the ambient sound waves around you and generate the opposite sound waves in order to reduce surrounding sound. Noise-cancelling devices have a built-in microphone which generates the opposite reversed sound waves to neutralise surrounding noise. Noise cancellation works best when the ambient sound around you is constant and around the low to medium pitch range. 

    Balanced soundwaves when ambient sound and noise cancelling waves match

    Now consider the fluctuating pitch levels when you speak. The sudden changes in pitch occur too frequently and make it difficult for any noise-cancelling audio device to analyse and process these differences. Therefore, some noises are heard whilst others are not.

    How to improve noise cancellation

    Turn off Adaptive Sound Control 

    Adaptive Sound Control changes the noise-cancelling intensity based on the ambient noise in your surroundings. The intensity of noise cancellation is increased in a loud environment and reduced in a quiet environment. Turn off the Adaptive Sound Control if you want the strongest noise cancelling level in any situation.

    To turn off Adaptive Sound Control 

    Optimise noise-cancelling (NC Optimizer) – for Headphones only

    The NC Optimiser function analyses the shape of your face, hairstyle, whether you are wearing glasses and even pressure changes on aeroplanes. Try to optimise noise-cancelling and see whether the noise-cancelling intensity improves.

    To optimise noise cancelling (NC Optimizer) 

    Make sure to wear the device correctly

    One of the easiest ways to maximise the noise cancellation capabilities of your audio device is to fit the device correctly. A tighter seal will already block out a certain level of ambient noise. Once you find the right fit, you should notice stronger noise cancellation. 

    To fit your earbuds correctly