Violin Forum/Message Board

[actonern]

The shape and profile of the bass bar has been alternatively described as critical to sound and not so important.

If a bar is place correctly in respect of the bridge foot and inclination, how important is its taper?

Some famous instruments have a rather "triangular" shape; cresting immediately toward the ends from a high point located near the middle or the "bridge foot" location... some are more elongated, as illustrated in Sacconi's book.

Any opinions on the best profile of the bar for sound?

Best regards,

[Jack H.]

I go for the smooth flowing curves.
it looks a lot nicer and is the more 'proper' way to do the job.

[Leif Luscombe]

The triangular shape is overly stiff. I have never encountered one on a good instrument.
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Leif Luscombe
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[Jeffrey Holmes]

[Andres Sender]

One procedure is to divide and conquer, as detailed by a known maestro. Details can be found by casting your maestro net for a second bass bar.

[Jeffrey Holmes]

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Jeffrey

http://holmesviolins.com

[JWH]

I would love to know the dynamics of a bassbar contour and how it fits in with different models of instruments.
What I see even today is talk about how a bassbar contributes to sound but no good study to define the linkage of different variables so one can definitively say, " this is happening at this point when this is changed." Instead, we hear that a bassbar should be 270mm long or better yet, short, sprung or not sprung, contour of the bar following the arching of the instrument, when I would guess, a bassbar has no idea what the arching is on the blind side of the top is. Some say, I think a bar should be 11mm in depth, some say 12, some say 13, some say 14 and even some who like 15mm. Some say it should be canted and placed perpendicular to the top, others say it should be vertical. Some say the high point should be at the center of the instrument, others say higher up toward the bridge line.

I've heard innumerable statements about how a bassbar contributes to tone and response, but nothing definitive on when, where, how, and why. Sorry, had to vent but this subject is frought with speculationand little fact.

[Jeffrey Holmes]

[JWH]

Good article, Jeffery. One I hadn't read before.

Would love to see a good study on this subject. Maybe, I'll start the mind-numbing process of switching out a couple hundred bars on a single instrument and see what I come up with. Second thought, maybe, I won't.

[M_A_T_T]

[Jack London]

Jeffrey said:
" I find that the actual shape, in the end, depends quite a bit on the instrument (arching). I use measurements that include the plate thickness to help plot the final curve.

Thickness and cross section profile are also factors in how the bar actually performs."

Could you give us some parameters that you use? Some idea of how the curve relates to plate thickness and arching, and also your observations about cross section profile and performance of the bar. thank you --- this could really help a lot.

[Jack London]

Jeffrey said:
" I find that the actual shape, in the end, depends quite a bit on the instrument (arching). I use measurements that include the plate thickness to help plot the final curve.

Thickness and cross section profile are also factors in how the bar actually performs."

Could you give us some parameters that you use? Some idea of how the curve relates to plate thickness and arching, and also your observations about cross section profile and performance of the bar. thank you --- this could really help a lot.

[Michael Darnton]

The system I outlined on Maestronet is, I think, the one Andres refers to.

Divide the length of the bar in half, half the halves, and do the same again. This will divide the bar length into eights (nine marks, total, counting the ends). I don't start exactly at the ends, but about 5mm inside, to allow for something like a bevel or Wurlitzer tab at the very end.

Make the height of the bar, including the thickness of the top (measuring with a graduating caliper), at each mark, from one end to the other, 5.0mm, 7.6, 10.2, 12.8, 14.0 (center), 12.8, 10.2, 7.6, and finally down to 5.0 at the other end. This makes a symmetrical bar, highest at it's center.

Map these dimensions out on a straight line on a piece of paper, and you'll discover something interesting. If you start your bar 40mm from the ends of the plate, and extend the given thicknesses down to zero, you'll discover something else interesting. As long as you're drawing things, mark in the plate thickness (a nominal 2.5mm) parallel to the baseline that represents the flattened outside arch surface, the ends of the plate, and draw in ribs and linings in their proper locations.

I am not the source of this plan; it was developed, as far as I know, by Carl Becker. The shape of the bar is exactly the same as the one I was taught to make by eye. Carl couldn't decide if the center should be at the center, or at the bridge, so he split the difference. I think that the support is needed at the narrowest spot between the f-holes and at the bridge, and if you put the center in the center, both spots are covered about equally.

The most important aspect of the heights of the bar is, in my opinion, to keep them symmetrical out from the center, very precisely. The exact cross section isn't as important, as long as, again, it's symmetrical out from the center. I was taught to make it bullet-shaped in the center, moving into semi-circular at the ends. Obviously, though, the cross section will affect the overall strength and weight of the bar, if you feel the need to change something in that direction. I usually make such changes as width and height rather than cross section.

The purpose for symmetry is to avoid generating dissonance in the vibration of the bar, from imbalance. You can probably achieve this by some exotic tapping routine (actually you can, and it's a PITA), but the caliper works as well and is faster.

I agree with Jeffrey, that mainly the bar has to do with response, assuming you make it correctly in the first place. You can damage all sorts of things with a incorrectly designed bar, though. I have experimented a lot with using the bar to change stiffness, and thus tone, on the bottom end, and have been able to damage the sound, but not do too much in the way of curing an instrument's innate problems in this area. My experience has been that the worst problems on the bass end usually originate around the perimeter of the plate, not from the area where the bar has influence, and that, therefore, the bar isn't likely to do much.

[JWH]

It's an immensely complicated subject. I think many of us for lack of data try and visualize the effects that a bar has on the top. Essentially a bass bar moves up and down by the rocking of the bridge foot, radiating sound waves to it's ends. I visualize (speculation) that the reason for little tone change is that once it's position is set, the top will undulate in the same pattern regardless of how stiff the bar is, so response, muting etc. are the primary variables affected. If one moves the center of the bar upward or downward, the center of stiffness will follow in the same direction allowing the bouts to change their flexibility and response. To that end, I can see where the upper and lower bouts might effect slight change of tone working mutually together, but separately it would seem that it's just a question of muting or non-muting of the same pattern of undulation.

It's been said that inclination of the bar off the center line of the top is not all that important, that it may have been more a design of strengthening by crossing the grain, yet I can't see where different placements wouldn't effect tone and response. Whether a bar is parallel to the center or inclined has to effect differences in the way the bouts vibrate. If we look at some of the stick-figure animations of how a top undulates how would not a bar that is rotated (maintaining point contact to bridge foot) across the surface not change that vibratory pattern? Just some thoughts.

And, Michael, what specifically do you find with respect to edge thicknesses that effect bass issues? Too thin? If so, what is a general rule of thumb for the way you graduate at the edges to mitigate those problems? John

[Michael Darnton]

When I have to deal with a bottom end problem, it's usually not my violin, so everything I do is remedial, not construction. I avoid it in my own instruments by the arching I use, and keeping track of stiffness as I graduate to make sure I'm not getting into some strange zone where I don't want to be. I don't graduate by stiffness, but I do keep an eye open in that direction, in case there's something weird about the wood I'm using.

Usually the problem relates to arching, or to wood stiffness. The last instrument like this I had to deal with had really floppy wood towards the edges--you could easily feel it--and the only thing that helped was a set of stiffening straps, which is a very intrusive thing to do, but I had tried everything else by that point. The straps worked. Someone previously had lined the whole perimeter with a layer of glued on silk reaching in about an inch and a half all the way around, so I wasn't the first person to think this way, but the silk hadn't done much. The graduations themselves weren't unusual, nor was the arch. I think it's just that the wood was unusually soft. Just on a basis of appearance, I wouldn't have used that piece.

Sometimes you can get relief by cutting a new bridge or moving the post around, but I've never seen huge changes from this--just small ones.

Spinning the bar relative to the centerline can be very detrimental--it changes what I guess you could call the linearity of the response in a really ugly way that you would never expect. I think that the traditional location is about as far as you can go in that direction, and less (more parallel) works fine, tonally, if one feels that the grain direction relative to the centerline is demanding that.