Sound Post Tap Tone Tuning Page by David Langsather
(revised 10/2020)
Page V_80
..The sound post has the important role of connecting the back and front plates of the violin and of keeping their motion in sync. It must have the proper acoustical tuning to do this at maximum efficiency.
.. The tap tone of the sound post should be the same as the back plate; that is: (227 1/2) HZ. This is the tap in the longitudinal (long) direction; which is the direction in which the sound post is in contact with the plates. {213 HZ from the side all along its length.}
...This sound post tap tone frequency can be measured directly through the top and back plates accurately by tapping down on either plate directly over the sound post location. It is verified accurate when the sound post is removed and retested by itself.
... The range of excellent performance appears to be perfect ( (227 1/2) HZ with a +/- ( 1) HZ) range.
...This really makes the violin tone sizzle when played, which a great benefit to both the player and listener. The tone becomes more stable and pure with this adjustment. Besides which, it is soooo "simple" to measure and adjust!
  Be sure to select wood on the Wood Tone Scale and having a Rub Tone of # 22, and from the top plate scrap wood if possible. If not, in "synchronous Resonance" with the top and back plates. See other areas for this information....
  David Langsather at Salem, Oregon, USA
..If you have yet to build your own wood reference tap tone tool, now is the time to do it! (see Tap Tone Technology section under: Useful Tools.)
...To see if your violin is a candidate for this improvement, just tap the center of the back plate (assuming it is at the ideal 242 HZ frequency) and then tap just over the sound post touching location. How close to harmony are the two tap tones? ..Our acoustical adjustment will be governed by whether the sound post tap tone is currently too high or two low (from in harmony with the back plate).
...On my own instruments, I mark the correct sound post contact location with the back plate with a special wooden pencil that has been reshaped to fit through the sound hole and mark right along side the sound post. I make a small pencil line aroung the base of the sound post so I can exactly replace the post. If the sound post is not currently marked, now is a good time to make a mark showing orientation and which way is up; this makes proper re-installation easy and mistake proof. [Remember, the slope of each end is different.]
...Now I put the instrument in a special holder which gives me a level plane for final positioning on reinstallation, then remove the sound post.
Direction of tap for tap tone...
..We want tap tone to be even all along length when we are done. Sand evenly around outside diameter of any section that is higher toned than rest of sound post.
Direction of tap for tap tone...
Direction of tap for tap tone...
..Sand this slight hour glass shape for raising the tap tone of the sound post to the (227 1/2) HZ goal. Be sure it also has an even tap tone all along its length, as described above.
..Sand this slight shape for lowering the tap tone of the sound post to the (227 1/2) HZ goal. Be sure it also has an even tap tone all along its length, as described above.
..That is all there is to it, and it really works!

(c) 2020 David Langsather
If end tap is too low:
If end tap is too high:
..I still feel this age, I need to preserve my memories!
213 HZ side tap tone evenly.
(227 1/2) HZ end tap tone.
Ideal Tap Tone...
........(227 1/2) HZ
Ideal Tap Tone...
........(213) HZ
Tap Here to hear tap tone reference.
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