How Speakers Work
Do you want to learn how speakers work? Speakers are probably the most important devices in audio and video and perhaps the least understood. To understand how speakers work you need to get a grip on how your ears work because, at its heart, sound is all about vibration. As well, speakers are essentially microphones used backwards. Microphones turn sound into electrical signals and speakers turn them back into sound.
When anything vibrates—a tuning fork, a guitar strong, or a drum head—it produces sound by moving the air particles around it. Your eardrums vibrate due to changes in air pressure caused by the thing that made the sound, like a bell, a train or a human voice, vibrating and moving the air. When the fluctuation wave caused by the vibration reaches your ear, it makes the eardrum vibrate, which your brain converts to sound. While it is true that sound can travel through water and other liquids and even through some solid objects, it most frequently travels through the air. So, in a sense, a speaker is a vibrator. A speaker produces sound-wave frequencies. The higher the wave frequency, the higher the pitch of the sound. The speaker also creates amplitude, or the level of air-pressure, which determines the volume of the sound.
At the center of the entire “sound” spectrum is what amounts to a pair of vibrating “converters.” A microphone takes the sound of a band, let’s say, and converts it from sound waves into electrical signals. These signals are saved by being recorded or encoded onto media like tapes, CDs, vinyl, cassettes or MP3 files. When the sound is played on an mp3 player or a stereo, the speakers, ear buds or headphones (ear buds and headphones are merely tiny speakers) do the exact opposite of what the microphone did in the first place; convert the electrical signals back into physical vibrations which create sound waves.
Physically, a speaker uses magnetism to reproduce sound. In every speaker, there is a winding of copper or aluminum wire called the “coil” and the coil is suspended over a stationary magnet mounted on a steel “top plate.” When electrical current travels through that coil it creates an “electromagnet,” which then interacts with the stationary magnet mounted in the speaker housing. A “cone” made of paper or plastic or some sort of composite is mounted atop the coil and fastened to the outside circular metal rim of the speaker. It moves up and down simultaneously with the movement of the voice coil.
As the electrical signals flow through the coil it becomes an electromagnet that either attracts or repels the permanent magnet. This is what moves the coil backward and forward and the speaker cone along with it. The moving cone pumps the sounds out into the air and, consequently, into your ears.
Speakers are everywhere, from inside your digital watch to outside at the football stadium. Although they vary in size from tiny to gigantic, they all work fundamentally the same.