With a market value set to reach $15.8 billion by 2025, chances are you own a pair of headphones. However, the odds of the average person knowing how they work are significantly worse.
At the most basic level, all speakers are made up of three main constituents: a cone (sometimes referred to as a diaphragm), a coil of wire and a permanent magnet. As shown in the main image, the cone is attached to the coil. The permanent magnet is situated within the coil.
Electricity is fundamental to the function of headphones – when it flows through the coil, it becomes an electromagnet. If the flow of the electricity is altered, the electromagnet either attracts or repels the permanent magnet. This combination of both attraction and repulsion induces motion in the coil, causing the cone to move. These movements generate vibrations (a.k.a. soundwaves) in the air – much like those produced by banging on the skin of a drum. As discussed in my previous post ‘How do we hear?’, the ear detects these vibrations and converts them into signals that can be processed by the brain.
Once the soundwaves are being produced, factors such as volume and pitch are controlled by the strength and frequency of vibration. In order to generate a louder sound, larger and more powerful vibrations are required. Pitches are determined by the frequency of the soundwave. The frequency is defined as the rate of the wave, illustrated by Figure 1. Whilst pitch is altered simply by increasing the power of vibration, frequency is governed more by the size of the speaker. Hence, huge subwoofers produce much better bass than a tiny in-ear headphone.
Although humans are capable of hearing many different types of sound, headphones and other sound-systems can typically only produce two: monoaural and stereo. Monoaural is when the sound only comes from one source, such as someone speaking. This is the type of sound encountered during a phone conversation or from an old radio. Stereo sound is encountered when two speakers generate slightly different vibrations in order to emulate a 2D soundscape. Have you ever had a song begin in one headphone and move across to the other? That’s an example of stereo. Whilst it is possible to generate 3D sound artificially, it is a lot more time consuming. To be effective, speakers must be placed around the audience and each must play subtly different things. Currently, the only place that this is practical is for ‘surround-sound’ in cinemas. Though, given the passage of time, it may well become a future household staple.
Image Creds: [http://www-cdn.sciencebuddies.org/Files/7472/6/speaker-diagram.png