The string section is the heart of the orchestra. String players often play continuously throughout a piece partially because of their ability to play without breathing, along with the wide range of dynamics and expressive potential that the instruments possess. Typical string sections contain 30 to 34 1st and 2nd violins, 10 to 12 violas, 10 to 12 cellos, and 8 to 10 basses. The violins make up the largest part of the string section. Violas and cellos are equal in number and the basses are the smallest section. Some string sections also include one or two harps.
The brass section has a homogeneous sound that can provide powerful accents, stirring melodies, and lush choirs of sound. This section is usually smaller than the other sections and may include three trumpets or cornets, three trombones, four horns, two euphoniums and a tuba. When combined, these instruments are capable of producing a massive wall of sound that can be dramatic and effective in loud sections. They are also capable of playing solos and breaking up into smaller sections for lighter segments.
Woodwind instruments have drastically different timbres than the other sections. They are not uniform in sound like the string and brass section. These instruments commonly double the string melody, provide color to chords, and act as a bridge between the string and brass sections. Orchestras commonly employ forces that include, in score order: piccolo, two flutes, two oboes, two Bb clarinets, and two bassoons. Some larger orchestras may include four saxophones, Eb clarinet, English horn, bass clarinet and contrabassoon.
The percussion section has both pitched and non-pitched instruments. While it is impractical to provide a list of every potential percussion instrument, several are used in most concert works. The pitched instruments include the timpani and barred instruments such as the xylophone, glockenspiel, marimba and vibraphone. The non-pitched instruments are the battery percussion and include various sizes of drums, including snares, bass drums, tom-toms and tenor drums. Most orchestras also use metal non-pitched instruments including cymbals, gongs, triangles and cowbells. There are also several instruments that are used for effect only, including wind chimes, wind machines, castanets, wood blocks and various other small percussion instruments.
The keyboard section involves any instrument that uses a keyboard to create sound. The most commonly used keyboard instrument is the piano. All major orchestras have access to a piano and pianists for when they are needed in the score. Sometimes, harpsichords and celestas are also used in an orchestra, although this is less common.