The modern definition of the word Orchestra tends to refer to the ensemble of mixed instrumentalists playing classical music. When you think of an orchestra, you imagine seventy or eighty or more musicians dressed in black on stage. This was not always the case.
In the musical time period known as Renaissance times (1450-1600) these musical groups not only accompanied vocal music, but played supporting music for drama. Ensembles playing this music were formed from instruments as varied as the harpsichord, viol, lute, recorder, cornett, sackbut, and organ.
The orchestras seen in the Baroque period (1600-1750) began to get bigger. Previous to this, vocal music was the most important music, and instrumental music was less so. The ability of the craftsmen to build instruments had improved to the point that the finest violins ever built were made around this time.
The orchestra of this time centered around the harpsichord. A harpsichord was like the piano of today, except a mechanical pick plucked the strings like a guitar, rather than a hammer hitting the strings like a piano. Violins, violas, cellos, and bass violins provided string sounds. Woodwind instruments like recorders, flutes, bassoons, and oboes, added color to the sound. Trumpets were used in orchestras as well, but were long natural trumpets without the more modern invention of valves. The timpani was the main percussion of the period.
Orchestras of the Baroque period were small by modern standards, numbering only about twenty to thirty players.
The next musical period is called the Classical period (1750-1825). During this period the orchestra grew to include 30-40 players. The brass section grew to include horns and trombones. Woodwinds included piccolos, clarinets, and contra bassoons (bass).
The Romantic musical period (1820-1900) brought new changes to the orchestra and it's instruments. The industrial revolution allowed for technical advances in the fabrication of instruments, especially the brass section with the invention of valved instruments. This allowed composers much more freedom in the parts they could write for all the instruments.
The tuba, bass clarinet, and many percussion instruments were added. This required additional string players to make the orchestra sound balanced. In his Symphony of a Thousand, Mahler had wrote for an orchestra containing one hundred and thirty musicians so it is clear to see with what enthusiasm composers explored the limits of possibility.
A current, professional symphony orchestra usually contains about seventy or eighty instrumentalists selected to fill the four sections of a modern orchestra; Brass, Woodwind, String, and Percussion. This will vary depending on the music being performed.
