Conversation so far:
What instruments were added to symphony orchestras?
Other instruments such as the piano, harp and celesta may sometimes appear in an orchestra.
What was the point of Beethoven adding instruments to symphonic orchestras?
Beethoven's use of piccolo, contrabassoon, trombones, and untuned percussion—plus chorus and vocal soloists—in his finale, are his earliest suggestion that the timbral boundaries of symphony might be expanded.
Did adding instruments to symphonic orchestras become common practice?
For several decades after his death, symphonic instrumentation was faithful to Beethoven's well-established model of timbral palette and harmonic flexibility.
What else did you find interesting about this section on Orchestras?
The term orchestra derives from the Greek name for the area in front of a stage in ancient Greek theatre reserved for the Greek chorus.
What details make the types of orchestras different?
The terms symphony orchestra and philharmonic orchestra may be used to distinguish different ensembles from the same locality, such as the London Symphony Orchestra and the London Philharmonic Orchestra.

Question: What changed in the Classical period?
Self-contained rewrite: What changed in the Classical period?