I've always wondered about the development and evolution of the design of instruments used in orchestra. There's a general standard of instruments for orchestra, how has that come about? Why is there a double bass, a cello, a viola and a violin and not more or less? Not only do the instruments cover different ranges but as far as I can tell they have their own unique sound to them as well. Maybe im wrong but it seems like if you were to start at the highest note of a violin and keep going down until you hit the lowest note then were forced to go to a viola or cello you would notice that a different kind of instrument kicked in and it wouldn't be a seemless downstepping transition. Why is this? Is there anything left to do in designing instruments to accompany an orchestra? Is there anything left to add out there?
To clarify my question lets look at a single instrument. A violin. What were they looking for when they designed the violin? Why does it look like it does, why does it sound like it does and why is eastern and western music equipped with instruments that sound different?
Finally, is it likely a newly designed instrument will come along and become as popular as the guitar or piano? Why or why not?