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..Opening up the instrument (by removing only the top plate) and re-graduating the plates from the inside:
...This is really the best method for an ideal outcome to violin plate tuning. Our goal is to have the violin plates at stable (unchanging) and ideal frequecies. In order to do this the violin plates we are adjusting should have reached equalibrium (are no longer subject to changes due to varnish, ground, or U.V. effects).
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...Click here to see an article on how to 'safely' remove the top plate and then to re-install it later...
...Next, determine what your plate frequency goals are, so you can work directly toward them.
...I would suggest you use 176 HZ for the top plate and 198 HZ for the back plate based on research of many years. (2017 conclusions...)
...Also,You want the top plate to be even all over (in the graduated areas) and the bass bar to exactly match the plate through out its length.
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...Research based ideal plate frequencies from Tap Tone Project (2017); as well as Wood Tone and Rub Tones for each violin part!
...I believe a good way to explain this process is to introduce some general principles to guide you; and then to give some examples and how to deal with those particuar situations:
General principle # One:
...If you want to increase the plate frequency, overall, remove wood from the center of the plate (center bout area).
   If you want to decrease the plate frequency, overall, remove wood from the two ends (upper and lower bouts).
General principle # Two:
...If you want to lower the tone of the wood in a certain area, make it thinner.
...It will be obvious that it is easy to remove wood and very difficult to put it back on again, so be careful! It is better to work slowly and approach your goal frequency in small steps than to try and do it all at once.
General guideline # Three:
...The edges thickness is to be maintianed (usually 4 to 4 1/2mm thick), and the plate wood across the ends of the plates inside should not be removed (leave it the same height as the edges for strength; as shown in photo below.)
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Protect these areas so no material is removed here...
(Top plate shown before "ff" holes were cut out); graduate toop plate to an even 2.6mm thickness.
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The raised sound post pad (tune to match the back plate frequency.) About the size of a quarter. Currently I would suggest eliminating this pad on the top plate.
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Areas to thin to increase the overall tone of the plate (by sanding or scraping inside surfaces); if only one end needs to have its tap tone frequency increased, then just scrape the center bout from the center toward the end that needs to be raised, beginning in the center of the instrument.
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Areas to thin to decrease the overall tone of the plate (by sanding or scraping the inside surfaces). If only the tap tone needs to be decreased at one end of the plate, then just thin the plate at that end..
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General Principle # Four:
...Complete the graduation scheme on the plate you are working on, (in my case as shown in the above photo, I continue working until all the black spots just disappear). Then we are ready to make our adjustments towards our goal frequency. Remember the adjustments we make now will be 'permanent'.
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...With my Opus # 20 violin, I exposed the plate wood for eleven days (24 hours per day) in my U.V. light box with the plates hung vertically {and a pan of water in the bottom to keep the wood from drying out excessively}(ribs glued to the back plate but the top plate not yet glued on, so the U.V. light was absorbed equally by inside and outside surfaces) until the wood had darkened to a pleasant 'suntan' color.
...You might consider an inside ground application now. The old master violin makers applied some substance that left a clear waxy surface that protected the wood from darkening even after hundreds of years. This inside surfaces must not be varnished, as this will hurt the instruments performance. I would suggest two coats of propolis application, followed by good two applications of dutch rush to these inside surfaces for best acoustical properties. If you use Propolis inside, be sure to also use it on the ourside as well. (see other articles).
...Then, after the body was glued together (after 1 1/2 days in a desicant drying bag to reduce plate moisture.. see separate article)
...This would be the time to apply any wood color stain to the body if you are going to. After this, apply any ground preparations desired. See separate articles on 'varnish ground'. [Including using Fuller's Earth' in first layers of varnish.}
...For varnish tips see separate articles on 'Varnish'.
...All this work is,unfortuately, necessary to achieve our goal for the plates too have specific and stable frequencies. ..Getting the plate tap tones correct is foundational to the sound the instrument will make over it's long life, and since it is not easily changed, might well be worth some time and effort to do correctly.
...Experience has shown that the actual tap tone frequency effects of ground application and varnish application and even varnish curing (see article in 'Varnish' section) are not significant enough to be concerned about. Work hard to get these suggested plate tap tone goal frequencies to 176 HZ top plate and 198 HZ back plate...both even all over graduated portion of plate.
...The next page will show examples of how the plate wood might be adjusted once the plate graduation is completed as outlined above. Because wood is variable in tone, it needs to be 'micro-adjusted' to our goal frequencies. This is probably why the more famous violins are not exactly uniform in plate thickness in different areas, there is considerable variation in the best violins and I suggest that it is because the inside of the plates were adjusted to get the goal of an even tone for the plates, rather than an exactly even wood thickness (graduation).
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Now, on to the next page of instructions....
top plate
back plate
top plate
back plate
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...Click here to see my latest plate graduation plan (2009-2017) for excellent power and tone. (Guarnarie plate graduation)...
(revised 11/2017)
Page AA_27
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..(2017) I would suggest that you review my latest dated articles on tap tone tuning and techniques, available throught out web site (see red ovals). Using new measurement techniques. click here...
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..Completed inside surface of the back plate of my Opus # 24 violin. The perimeter depth graduation marks show because there needs to be a curve here instead of a sharp edge, to prevent future cracks.
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.A bundle of dutch rush ready for circular scrubbing into the wood surface of the interior; do this twice.
..Push and use a circular motion. After doing the entire surface, go back and do it one more time for maximum effect. Notice the smooth and waxy feel to the wood surface.
..Also note the acoustical effect of tap tones on areas done and undone areas; very impressive improvement... Also not how the effect goes through to the outside wood surfaces, the same as the effect on the inside surfaces. This appears to be a permanent change in the sound characteristics of the violin wood plates.
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..These general plate tuning instructions relies on the Mode #5 lines as the actual junction between the middle area and upper and lower bout areas.
..CLICK HERE to see a video showing how to mark out these lines with a piece of white black board chalk.. Listen from 0:50 to 2:42, for this instruction....