At its most basic, an orchestra is a large instrumental ensemble that contains sections of string, brass, woodwind, and percussion instruments. The orchestra grew throughout the 18th and 19th centuries, but then changed very little in composition during the course of the 20th century. The writing of the prominent composers of each historical period determined the “standard” size and make-up of that particular period. A smaller-sized orchestra (forty to fifty musicians or fewer) is called a chamber orchestra. A full-size orchestra (eighty to one hundred musicians or more) may be called a symphony orchestra. A philharmonic orchestra does not indicate any difference from a symphony orchestra, but can be useful to distinguish different ensembles based in the same city (for instance, the London Symphony Orchestra and the London Philharmonic Orchestra).
The instrumentation requirements of orchestras became somewhat standardized in the Classical Period (1750–1820), based on the compositional habits of the most prominent composers of the period (Haydn, Mozart, Beethoven), which were in turn largely influenced by the possibilities of the instruments available to them. For example, the Baroque orchestra you hear on the SNS Baroque Series does not typically employ clarinets, for example, as it was not invented until around the turn of the 18th century. The 19th century woodwind section also saw an expansion in the number and types of instruments, with increasing use of the piccolo flute, the English horn, the bass clarinet, and the contrabassoon. Valves for brass instruments were not invented until the early 19th century, at which point there was a rapid growth in both the number and the prominence of trumpets and horns, beginning primarily with the works of Hector Berlioz. With the rise of the rest of the brass section and the invention of the tuba, the trombone found a regular home in the symphony orchestra, whereas its use was previously limited primarily to liturgical settings. As the number of woodwind, brass, and percussion instruments increased, the size of each string section also increased in order to balance the output of the different sections of the orchestra.
The actual number of musicians employed in a particular performance may vary according to the work being played and the size of the venue. Symphony Nova Scotia employs thirty-seven musicians on a full-time basis, and hires per-service musicians on a concert-by-concert basis, depending on the instrumentation required by a particular program. So the basic size of Symphony Nova Scotia determines much of the programming you hear, with a primary focus on Baroque and Classical music. Performing repertoire from the 19th and 20th centuries typically means that extra musicians need to be hired. Bringing our audience a wide variety of programming within these parameters is a challenge we embrace!