The Anatomy of a Speaker: Pt 1
13 Dec 2014
A speaker is a device known as a transducer. This means it converts one form of energy into another. In the case of a speaker, it converts the electrical energy of an audio signal into the kinetic energy of sound.
Speakers evolved from the development of the telephone by Johann Philipp Reis, Alexander Graham Bell, Thomas Edison, Nikolai Tesla and others in the 1870s. Electrical speakers began replacing acoustic horns for sound reproduction by the 1920s.
The most common type of driver is a dynamic loudspeaker. A cone made of paper (or a similarly lightweight material such as cloth, plastic, aluminum, Kelvar, or even carbon fibre) is connected to a round frame called a basket using some kind of flexible suspension material that allows the cone to vibrate as a diaphragm. In the center of the frame is a voice coil, which is a magnet wrapped in fine wire. When an electrical audio signal is applied, the voice coil vibrates, causing the cone to move back and forth. The result is that the electrical signal becomes sound.
Speakers must be able to faithfully produce sounds through the entire range of human hearing which begins at roughly 20 Hz and extends to beyond 16,000 Hz. Because it is extremely difficult for a single drive to reproducer all those frequencies, multiple drivers used to create better sound.
Deep notes require larger cones because of the volume of air that must be moved to reproduce those sounds. High notes don’t need to move much air but the drivers have to vibrate very quickly. This is why many speakers often include two or more different drivers, each responsible for reproducing sounds in specific frequency ranges.
Electrical audio signals are separated into defined frequency ranges by a crossover. It ensures that the right frequencies go to the right drivers: Woofers, midrange and tweeters.
- The tweeter takes care up the upper frequencies, usually starting at 2,000 Hz and extending upwards of 20,000 Hz.
- In some speaker set-ups, the mid-range driver produces frequencies from approximately 300 Hz to 5,000 Hz. Another name for mid-ranger speaker is “squawker.”
- A driver that produces very deep notes is called a subwoofer. It typically is entrusted with audio below 300 Hz.
- The woofer is the driver in charge of low frequencies. Depending on the speaker design, it may also have to handle a portion of the midrange frequency spectrum.
- Some speaker designs divide the frequency range up even further and may include a super tweeter for ultra-high sound and a subwoofer for extremely low bass.