All bowed stringed instruments ideally should have all of the following five characteristics…
In my opinion the sound quality of good violins should be the same in old and new violins.
A well made violin should have five main features which are an absolute necessity.
1. the violin has to be structurally well made of high quality well seasoned timbers crafted in an aesthetically pleasing and artistic manner.
2. the violin has to have an even tone over all four strings.
3. the violin has to have a carrying sound so it can be heard in the last row of the concert hall (please do not confuse with a loud tone)
4. the violin has to speak easy under all conditions in all registers of all four
5. the violin should be well set-up and easy to play
These are the main features which make a good violin.
Then you will find the character of an instrument: some instruments are more powerful, some have a more soft sound, some a brighter sound etc. These are all characteristics which come down to the taste and requirements of the player.
I have heard many famous old instruments as well as many new instruments which do not meet these main features. Some have a lack of all of them, some only have a weakness in one area.
My advise is to look for the top five main features which make a good violin when you choose a new instrument. Enjoy