system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is an orchestra so big? How can 20 cellos improve the music in a way 5 cellos can't?
gpt
3 reasons:

1. Orchestral compositions have a lot more separate parts than you realise.

2. Two cellos playing in unison sound "bigger" than just one, for obvious reasons, even if you match the volume.

3. When the orchestra started to take shape, there was no electronic amplification.  Especially for the lower frequencies, it was very hard for a single instrument to fill a hall with a pleasing listening level.  Really, only the piano and the organ could do it effectively on their own, other instruments had to be multiplied to make them loud enough to be heard.  Even though you can now make a single cello as loud as you damn well please, if you want classical music to sound the way it did when it was first written, you need to play it the way the composer would have heard it.