You must have noticed from my first blog post that I am a huge fan of music and hence I like to enjoy my music to the fullest. Unfortunately, background noise is heard when I listen to music on the go. For example, when I am travelling in a bus, I hear phone conversations and sometimes loud crying of babies, which is very disturbing. There is a solution to this, which is noise-cancelling headphones but unfortunately I do not own one because they are very expensive. But I will tell you how they work.
There are two types of noise-cancelling headphones, namely active and passive. The latter are manufactured to maximise filtering of noise of about 15 to 20 dB by using material such as layers of high-density foam or other material that absorb sound. Due to this reason, these headphones tend to be heavier than ordinary headphones. Active noise-cancelling headphones perform the same task as passive ones but they have some extra features. Sound waves with high frequencies can be blocked because of the structure of these headphones. The incoming noise is in anti-phase with the sound waves produced by the speakers in the headphones. In other words, destructive interference takes place, which is shown in the figure given below.
Figure : Cross-section of a set of noise-cancelling headphones
Let’s look at the components found inside these headphones.
- Microphone – The embedded microphone receives external sound waves, which cannot be blocked passively.
- Noise-cancelling circuitry – The electronics fitted inside the ear cup sense and generate a model of the incoming sound wave and stores information such as the frequency and the amplitude. An anti-phase wave is then created to cancel the noise.
- Speaker – The anti-phase wave of sound produced by the circuitry is fed into the speakers along with the audio produced by music; destructive interference takes place erasing the noise and the desired sound is produced in return.
- Battery – This provides the energy required for the noise-cancellation process. The battery found in modern active noise-cancelling headphones (eg. new Beats Studio) can be recharged by plugging the headphones to the computer using the USB cable provided with the headphones.
HowStuffWorks “Noise-canceling Headphones”. 2014. HowStuffWorks “Noise-canceling Headphones”. [ONLINE] Available at: http://electronics.howstuffworks.com/gadgets/audio-music/noise-canceling-headphone3.htm. [Accessed 24 March 2014].