Violin Bass Bar Notes and Observations....
Page V_75
..Length of bass bar: The traditional length of the full sized bass bar is 10.5" and the over all length of the top plate is 14".
..I suggest that this ratio: ( 10.5" / 14" = 0.75) can now be used to determine the length of any bass bar in any size stringed instrument. To discover the target length of the proper bass bar, measure the overall length of the top plate and multiply by 0.75; the answer is the proper length.
..To determine the proper position inside the top plate, just make the distance the same on each end of the bar to properly center the bass bar.
...Then shape the bottom of the bass bar wood to perfectly match the contour of the inside surface of the top plate at the bass bar location.
..Prior to gluing the too tall bass bar stock into plate; first apply a thin coat of hide glue to the glue line and allow to dry. This will ensure the best acoustical interaction and help prevent wood distortion which might show through the top plate wood.
..Full full sized violin the width of the bass bar stock is 5mm or a little more, (I am currently using 5.5 mm / 0.217" wide) ; and I suspect this can be scaled up or down for other instruments with good results.
...The proper wood for the bass bar:
..The bass bar is made of spruce wood; quarter sawn; with three to five grains of growth wood. It should ideally be made from the same piece of wood as the top plate (as well as the wood for the end and corner blocks) for best acoustical results in the finished instrument. { 198 HZ on the Wood Tone Scale}
..If this is not possible, then stroke the top plate wood along the long axis and listen to the hiss sound (the 'rub tone' of the wood). Select wood for these other parts with the same rub tone as the top plate. {Best to use # 22 Rub Tone for all violin parts} {Please see articles on 'rub tone' under the 'acoustical' section for a complete discussion on topic).
..The bass bar stock is made too tall and once glued in place and allowed to dry overnight; it should be shaped to give a tap tone (downward tap all along the length of the bass bar) of 176 HZ; the same as the top plate.
Neck end
End Pin End
1 "
2 "
3 "
4 "
5 "
6 "
0 "
-1 "
-2 "
-3 "
-4 "
-4.5 "
Finished bass bar height on high side (toward center line of plate: {side profile}
..It is tapered on its sides toward the top and the top is rounded over slightly...
Inside curve of top plate turned upside down.
..This is the finished dimension of the new bass bar for my Opus # 29 research violin which I acoustically tuned on 4/2018.
..Of course each bass bar will be slightly different because of different wood but your bass bar should be close to this. What I recommend, is that you begin with lines higher that these measurements and then shape down until the tap tone is even all along the top surface and the same as the top plate tap tone (tap in the center of the plate between the small upper sound holes as a reference...which idealy should be at 176 HZ (on the piano, the F note below middle C is at 174.6 HZ untempered; which should be a very good guide).
..Or better still, use the below acoustical tap reference:
(C) 2018 by David Langsather
..Bevel the two ends at a 45 degree angle at finish, just enough to make the fingernail tap of the end of the plate wood quiet.
Ideal Bass Bar Tap Tone Reference.....176 HZ
..As a final test, strike the center of the back plate with the fingertips and palm of you hand and then immediately the center of the top plate (that you are just tuning) to compare. If the plate is tuned correctly, it will be a quiet even calm sound.
..Now turn your hand over and tap the two plates with the fingernails all at once and compare the back to the top plate. If the top plate is noisy and different than the back plate, the top plate bass bar is probably not tuned correctly.
Shape Profile of Bass Bar near center.
Shape Profile of Bass Bar far ends.
...As a guide for fine tuning the about completed bass bar; tap along the bass bar on the outside of the top plate with back of the fingernails of the two center fingers gently. As you tap along, listen for any suddenly noisy areas. Exactly opposite, the bass bar will be either too high or low. Slightly reshape until it becomes 176 HZ Tap Tone. Recheck to verify that the problem has been fixed. When you get to the two ends of the plate, the tuning of the end of the bass bar determined whether these important end areas are quiet or noisy. It they are noisy, then adjust the last 3/8" or so of the bass bar until they are quiet like the rest of the plate.