The instrument family which really developed well are the western string-instruments. A lot of modernization like the longer strings (out of metal instead of catgut) with more tension or the straight-concav bow increased the volume of the instruments to be able to play e.g. concertos with orchestras. However the most important thing was never touched and will be never touched:
The fretless fingerboard.
This fingerboard makes it so difficult to learn the as instruments and intonation is THE topic for the string players. This difficulty - or lets say weakness (again a stupid instrument?) - is the strength of the violin family: it is possible to play every scale also in every non tempered tuning you could imagine, you can make all kind of glissandos, portamentos, vibratos you like to. The string instruments are the the instruments with the widest range of sound colors. These Instruments are a good example for successful modernization and should be a model fort instrument development.
