All sound comes from vibrations. Sound waves are longitudinal waves, and sound needs a medium, which can be solids, liquids or gases, to carry it. In air at room temperature the speed of sound is about 345 meters per second. It is about 1,500 in water and 5,000 in steel. Sound is slower than light, so the flash of an explosion is seen well before its sound is heard.
Pitch is the perception of frequency, and a sound's frequency is how many vibrations happen each second. The faster something vibrates, the higher the pitch. A tube or string has a lowest resonant frequency, called the fundamental. The higher ones are overtones, and all of them are called harmonics. The same note on two instruments has the same fundamental, but the mix of overtones differs. That mix gives each instrument its own sound, called timbre.
The eardrum vibrates from sound waves and sends the vibrations to three tiny bones in the middle ear: the malleus, incus and stapes. People can hear from about 20 to 20,000 hertz. The louder the sound, the shorter the time it takes for noise-induced hearing loss to happen. Listening for a long time to sounds at or above 85 decibels can damage hearing.
A string on its own makes little sound, because it is thin and slips easily through the air. A string instrument is made of wood, and the hollow body pushes the air and makes the sound louder. The violin emerged in northern Italy in the early sixteenth century. It has four strings tuned in perfect fifths: G, D, A and E. A guitar usually has six strings. An electric guitar makes little sound unless it is plugged into an amplifier.
Most woodwinds have a reed, a small piece of cane or wood that vibrates when air is blown across it. A flute has no reed. Its sound comes from air blown against an edge, making the air in the tube vibrate. A flute or oboe player opens and closes finger holes to change the length of the column of air. In a wind instrument a longer tube makes a lower note. A trombone player changes the tube length with a sliding tube. Modern trumpets have three piston valves, each of which increases the length of tubing.
A drum has a drumhead, which can be animal skin, fabric, plastic or fiberglass, a body, and a way of attaching the head to the body. Percussion instruments make sound when they are hit, shaken or scraped. Almost every modern piano has 88 keys, which is seven octaves and a bit. A pipe organ is built with many tubes of fixed lengths, each making a different frequency.
Erich von Hornbostel and Curt Sachs published a system for sorting instruments by how they make sound in 1914. An orchestra has four groups: strings, woodwinds, brass and percussion. A full symphony orchestra has from fifty to one hundred or more players, and a smaller chamber orchestra has about fifty or fewer. The principal first violin is called the concertmaster. The oboe often gives the tuning note.
One of the oldest flutes was made from the naturally hollow wing bone of a griffon vulture, with five finger holes and a V-shaped mouthpiece. Its pieces were found in 2008 at Hohle Fels, a Stone Age cave in southern Germany. Jiahu, in China, was inhabited from 7000 BC to 5700 BC, and its bone flutes are between 7,000 and 9,000 years old. In the late 1930s, steel pans began in Trinidad and Tobago, and the main object used to make them was a 55-gallon oil drum.
Words to know
- medium: what carries sound
- frequency: vibrations a second
- timbre: a sound's color
- harmonics: overtone family
- percussion: hit instruments
- overtones: higher resonances
