String instruments comprise the largest section of a symphony orchestra and are positioned at the front of the orchestral layout. The sound from a string instrument is caused by the vibration of strings over a hollow wooden sounding board. Most often, this vibration is caused by the movement of a bow over the strings. However, in the case of the harp, the vibration is caused by plucking the strings. The instruments which comprise the string section of a symphony orchestra are first violins, second violins, violas, cellos and double basses. One or two harps may also be part of the symphony orchestra.
Woodwind instruments are arranged in the middle of the symphony orchestra layout. The sound from a woodwind instrument is caused by the vibration of the air column in the instrument, which is a hollow tube of wood or metal. All woodwind instruments, except for the flute, use a reed to make this vibration happen.
The instruments in the woodwind section are grouped so as to extend to high and low reaches of the orchestra. The instruments which comprise the woodwind section of a symphony orchestra are the flute (including alto and bass flute), piccolo, oboe (including bass oboe), cor anglais, bass oboe, clarinets and bassoon. Saxophones may also be part of the woodwind section in a symphony orchestra.
Brass instruments often sit behind the string and woodwind sections in a symphony orchestra on raised platforms. The sound from a brass instrument is caused by the vibration from the musician's lips on a mouthpiece attached to a metal instrument in various tube and bell shapes. Other than the trombone, which uses a slide, all brass instruments use keys to create the various notes. The instruments which comprise the brass section of the symphony orchestra are the trumpet, cornet, trombone (including the alto and bass trombone), French horn and tuba.
Percussion instruments sit at the back of the orchestra. Such instruments make sound by being struck or shaken. Percussion instruments can be grouped into three categories: tuned, untuned and keyboard. Not all percussion instruments will be included in a symphony orchestra. Some examples of percussion instruments are the xylophone, bass drum, tympani and piano.