There are three areas of the violin which strongly radiate sound, namely the side (rib) structure, the top plate (belly) and the back plate. The sound these contribute largely determine how successful a particular instrument is.
Occasionally one hears a musical instrument so outstanding in tone production, that the listener notices it separately from the talent of the performer or the beauty fo the music. I believe that special 'something-extra' is due in large part to building a particular violin so that each part is compatible to the structure around it acoustically.
Each part has a natural vibration frequency that can be heard with a gentle tap. When the part it is attached to has this same frequency, sound passes between them with minimum interference of loss.
Unless I am mistaken, this was the method used by the famous violin makers of the past to determine the final shape of the various wood parts (I.E. "acoustical tuning").
There is enough natural variability in wood so that even if ten identical copies of a famous instrument were prodced, some copies would be considered more successful than others. The acoustical (final) tuning approach adjusts for this allowing a consistent musical result.
As each major wood part of the violin is completed, it is finally shaped so that it produces the desired tap tone (frequency).
Thus the parts work together and the completed insturment is successful. The wood parts that I tune this way (in order of completion) include: top plate (belly), bass bar, back plate, rib structure, completed neck-fingerboard, bridge, sound post, tail piece, end pin, and tuning pegs.
