Many years ago, some composer had the bright idea to write a piece of music for a large group of musicians, and they called this group an orchestra. In those days, a large group meant only a dozen or so1, but since then orchestras have grown, and a modern orchestra may have over a hundred instruments.
There is more than one type of orchestra: Symphony orchestras2 are large and play any orchestral music; Chamber orchestras are much smaller and play chamber music; Ballet and Opera orchestras play for Ballet and Opera companies; Session orchestras are brought together to record film and television scores.
Orchestras may play on their own, or accompany soloists or choirs: the number and type of instrument involved can vary tremendously depending on the era and composer of the music being played.
The orchestra is directed by a conductor who stands on a little platform, waves a stick, and gets his name on the programme. Originally they were conducted by the First Violinist, or from a harpsichord or piano, but as they became larger this became impractical: the conductors gave up trying to do two jobs at once and began instead to concentrate on the tricky task of keeping a large number of very different instruments in time and balance with each other. Their job is made easier by the section leaders or Principals who co-ordinate their own sections during rehearsals.
The orchestra is usually divided into four sections, sometimes five:
Stringed instruments are generally made of wood, with the strings made of gut or metal. Sound is produced either by drawing a bow of wood and horsehair across the strings, or by plucking them with the fingers.
The four main types are Violins, Violas, Cellos and Double Basses. The first three are the Violin Family, and are quite similar to each other: violas and cellos are basically violins scaled up. Double Basses are usually mistaken for members of the same family, but are in fact related to viols. All these are usually bowed, but can be plucked3.
Guitars and Harps are also stringed instruments, of the plucked type. Harps are used in many orchestras, some pieces calling for several instruments. Orchestral Guitars are not so common, but are still sometimes used.
Although it has the fewest types of instrument, the string section is the largest in the orchestra, with as many as a dozen players to each part. The violins are divided into two large groups, referred to as First and Second violins. Both sections have a Principal: the Principal First Violinist is known as the Leader of the Orchestra.
Woodwind instruments are made of wood, except those which are made of metal4.They are instruments in which the sound is produced by the player's breath.
The four core instruments are Flutes, Oboes, Clarinets and Bassoons; there are also auxiliary instruments such as the Piccolo (a little flute), English Horn5, Bass Clarinet, Saxophone and Contrabassoon.
This section can be further subdivided: Clarinets and Saxophones are single reed instruments6, while Oboes and Bassoons are double-reed instruments7. Flutes have no reed, and their sound is produced by the vibration of the players' breath against the lip of the mouthpiece.
There is a Principal for each family of instruments. The players all double on instruments where necessary, with the Principal usually playing the higher instruments: for instance, the Principal Flautist often plays the piccolo as well, while the second or third flautist may double with an alto or bass flute.
Brass instruments are made of metal, but they don't have to be: the obsolete Serpent was made of wood, and the earliest instruments were hollow animal horns. They are instruments in which the sound is produced by the vibrations of the player's lips against the mouthpiece.
The most common instruments are Trumpets, Trombones, Horns and Tubas, but there are many others: the Euphonium (a little tuba), the Cornet (a bit like a trumpet, but actually a type of horn), the Sousaphone (which goes right round the player's head) and the Wagner Tuba (more like a horn than a tuba).
Most brass instruments are valve instruments; opening a valve introduces a new section of tubing and drops the sound by a specific amount. The pitch of the note also depends on the players' lips, as each fingering is the basis of an harmonic scale: this means that a trumpet with three valves can play in several octaves.
The trombone operates differently: although it still uses the harmonic scale, it has no valves and the length of the tubing is adjusted by means of a slide - an outer section of tubing slides along an inner section.
There are other variations: baroque trumpets and bugles, which have no valves and play only the harmonic scale; and slide trumpets, which work the same way as the trombone; but these are not common orchestral instruments.
Percussion instruments are those in which the sound is produced by means of hitting the instruments. This section is the special effects part of the orchestra. It is by far the most diverse section, and Percussionists are expected to be able to play all of the many instruments that may be required.
There are too many types to list: they range from the Drums8, to Xylophones, Cymbals, Triangles, and Woodblocks. It includes instruments which are not percussive at all, such as slide whistles, and special effects noise makers, from the Whip to the Cannon used in the 1812 Symphony.
Some pieces require quite bizarre percussion: Chain, Anvil and Wind Machine are among the more well-known. The percussion section can basically include anything which can't run away during the concert.
The only thing most keyboard instruments have in common is the keyboard. The section includes the Piano (a percussive stringed instrument), Harpsichord (a plucked stringed instrument), Organ (a wind instrument) and Celeste (a percussion instrument dressed up with a keyboard).
This section doesn't appear in all orchestras, and it is rare to have more than one type of instrument at a time (and even rarer to have more than one of each type).