Copyright © 2007 Dorling Kindersley
Music is one of the glories of sound. When a musician plays a note of a certain pitch, the musical instrument vibrates or RESONATES and produces a complex pattern of sound waves made up of many different frequencies. The most noticeable sound wave is called the fundamental, but there are other waves with higher frequencies, called harmonics. Notes from a flute sound more pure than those from a saxophone because they contain fewer harmonics. Musical instruments often make very quiet sounds, but some are designed to AMPLIFY the sounds they make so we can hear them more easily.
Resonance is the sound made by a vibrating object. If you tap a large wine glass, it produces a low musical note. If you tap a smaller glass, it makes a higher-pitched note. Although objects can vibrate at any frequency, each one has a particular frequency at which it vibrates much more powerfully. This is called its resonant frequency.
Opera singers can shatter a wineglass by singing a note that is exactly the same as the glass's resonant frequency. When the singer sings the note, the glass begins to vibrate and "sing" the same note itself. If the singer holds the note for several seconds, the vibrations become extremely powerful, shaking the glass until it smashes.
Making sounds louder is called amplification. Most musical instruments have a part that vibrates and makes sounds, and another part that makes the sounds louder (amplifies them). On their own, the vibrating parts may make quiet sounds that would be impossible to hear, even from nearby, if they were not increased in volume. Vibrating guitar strings are amplified either by a soundbox or by using electricity.
Under the steel strings of an electric guitar, there are tiny magnets that generate small amounts of electricity as the strings move. These currents are fed into a separate piece of equipment called an electronic amplifier. This increases the current many times and uses it to play the sound of the guitar through a loudspeaker.