I want to mention a summary of the recent tap tone research, so far (2017). This information might prove useful in isolating acoustical problems or in selecting a violin for yourself.
  In its simpilist form, the tap tones of these areas should be in their correct relationshipa in order for the best acoustical playing condition.
The underside of the scroll tap should be at 198 HZ.
The underside of the neck, the fingerboard's top surface, / bass bar and top plate should match and be a 176 HZ.
The bridge, sound post, tailpiece proper, nut / saddle / end pin/ nut / ribs and saddle, as well at the back plate and sound holes be at 198 HZ...
..The string bar of the tailpiece should have a vertical tap tone of 242 HZ for quick response.
Tapping with the unsharpened side of the wooden tip of an ordinary wooden pencil (or similar tap tool) should give good results.

Next, current research shows that the frequencies of these parts should be at certain ideal frequencies. These then order the set of tuned frequencies for each individual part so that the violin works in unison acoustically. These frequency pairings (based on combination of Solfeeggio and C.37.C theory) are as follows:

142.5..................142.5..........

150.0..................148.5...........

161.0..................160.0.....

177.0..................176.0.... Top plate and , underside of the neck, fingerboard top surface, and ............................................bass bar.

188.0..................185.3.....

198.5..................198.0......Back plate, bridge, sound post and tailpiece proper. nut, ...........................................saddle and side tap of the ribs.

213.5................. 213.0.......

...Now what about plate graduation before acoustical tuning?
... I would suggest this practical guide;
...For the top plate, make the plate 2.6mm even all over (except ends and edges).
...For the back plate, use my latest Guarnarie back plate graduation plan.
...I suspect the results will reward your efforts!
(c) 2017 by David Langsather

C.37.C (HZ).......Solffeggio (HZ).........

                                                                                             
Violin Saddle Adjustment....
(revised 1/2013)

(modified 9/2017)
Page AA_40

242.0...................242.0 ..... The string bar of the tailpiece

..Successful Instruments Acoustical Relations...

Please see latest information about Wood Tone /Rub Tone as well as Tap tone, in other areas...