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Bass bar height?


Polk
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I have a...I think Chinese fiddle here (no label) that sounds good but doesn't really favor the bass all that well. I popped the top today to fix a small crack and discovered that the highest part of the bass bar (which otherwise looks fine) is 15mm high above the plate. Seems a bit high...no? Isn't 12mm more like it? Please advise. Thanks!

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I was rereading Joe Curtin's Strad Trad Secrets bass bar article recently and he talks about generally having his at about 14 mm at highest point (which is shifted to position of bridge and not in "center").  I have been experimenting some with this on my last few violins and haven't decide yet if I like it or not.

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15 mm could be better or worse than 12 mm, it depends on a host of other factors.

David I think some makers change bar heights more than I do. I tend to use a height of 14 mm measured through the top for new violins with arch heights of 14-16 mm. If you don't mind elaborating on this, when would you use a lower or higher bar and what would you expect to result from those changes?
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I've noticed as a general rule, the height of the bar is often flush with a straightedge resting on the edges of the C bout region and spanning across the plate.

Hi Bill, Just trying to think this through and I may have your meaning wrong.  With the bar height flush with the bottom of the plate (gluing surface) then the lowest arch gets the shortest bass bar and the highest arch gets the tallest bass bar.  If I understand arches correctly, taller arches are stronger than flatter arches of the same thickness.  Thinking of the bridge (cars, pedestrian, etc.)  analogy where an arched bridge can support more weight than a flat bridge, it seems a flatter arch would need a taller bass bar than a belly with a higher arch.  Am I understanding correctly?

 

-Jim 

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Hi Bill, Just trying to think this through and I may have your meaning wrong. With the bar height flush with the bottom of the plate (gluing surface) then the lowest arch gets the shortest bass bar and the highest arch gets the tallest bass bar. If I understand arches correctly, taller arches are stronger than flatter arches of the same thickness. Thinking of the bridge (cars, pedestrian, etc.) analogy where an arched bridge can support more weight than a flat bridge, it seems a flatter arch would need a taller bass bar than a belly with a higher arch. Am I understanding correctly?

-Jim

You could also look at it like this:

Weaker wood needs a higher arch and (maybe) a taller bar. Stronger wood needs a lower arch and (maybe) a lower bar.

That's assuming wood strength and arch height are in agreement on a particular instrument.

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Okay. I did take the arch height into consideration, the arch itself being rather low (between 12 and 13mm). Turns out that the bar height from the gluing surface up was about 14mm. I cut it down to just under 12mm and cleaned it up a bit, then put the fiddle back together. bass is fine now with clean deep bass projection. I'm quite satisfied. Thanks all for the suggestions!

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You could also look at it like this:

Weaker wood needs a higher arch and (maybe) a taller bar. Stronger wood needs a lower arch and (maybe) a lower bar.

That's assuming wood strength and arch height are in agreement on a particular instrument.

Thanks C1, that approach makes sense.  Now if I could figure out if a wood is weak before carving the arch.  :unsure:   But that would be a topic for a different thread.

 

Polk, it's nice to hear that you resolved your bass bar issue to your satisfaction.

 

-Jim

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The higher the arching, the lower the bar.

The lower the arching, the higher the bar.

 

Based on lore that the violin bar was once left integral with the wood of the top, that would be a good place to start with if all other parameters are in the area considered normal.

 

I suggest that before lowering the bar you might thin it first. This gives a lot more flexibility and springiness to the plate while leaving quite a bit of strength.

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Hi Bill, Just trying to think this through and I may have your meaning wrong.  With the bar height flush with the bottom of the plate (gluing surface) then the lowest arch gets the shortest bass bar and the highest arch gets the tallest bass bar.  If I understand arches correctly, taller arches are stronger than flatter arches of the same thickness.  Thinking of the bridge (cars, pedestrian, etc.)  analogy where an arched bridge can support more weight than a flat bridge, it seems a flatter arch would need a taller bass bar than a belly with a higher arch.  Am I understanding correctly?

 

-Jim 

This only applies to moderate arching like Strad used; if you're dealing with some of the bloated German instruments of bygone years, it all goes out the window.  As I mentioned, this is just a general observation gleaned from looking at many instruments and shouldn't be regarded as a hard and fast rule.

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  • 7 months later...

I need to replace a bass bar in a 3/4 size violin.  The existing one is so crude, whittled so carelessly and is popping off the plate, that I don't trust using its current height.  Is there any rule of thumb about bass bar heights on fractional violins?

On 6/25/2016 at 6:44 AM, Bill Yacey said:

I've noticed as a general rule, the height of the bar is often flush with a straightedge resting on the edges of the C bout region and spanning across the plate.

I also may have to replace the bass bar on a 1/2 size violin.  What do others think of Bill Yacey's general rule?

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I'm replying to my own post --- a better idea seems to me to use the Weisshar-Shipman dimensions for a 4/4 violin bass bar thickness of 5.5-6 mm and 13 mm bar height measured from inside at center, and scaling down proportionally.  Ratios are 2.36 -2.17 for violin, 2.3 - 2.15 for viola, and 2.19 for cello (using data table on page 28 of the W-S book).  Would appreciate any comments on this method for bass bar heights for fractional violins.

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On 6/26/2016 at 9:40 AM, nathan slobodkin said:
On 6/24/2016 at 9:03 PM, David Burgess said:

15 mm could be better or worse than 12 mm, it depends on a host of other factors.

David I think some makers change bar heights more than I do. I tend to use a height of 14 mm measured through the top for new violins with arch heights of 14-16 mm. If you don't mind elaborating on this, when would you use a lower or higher bar and what would you expect to result from those changes?

I go through a rather convoluted and time-consuming process of stiffness measurements.Various weights applied to the top and back on a jig, and deflection measured at various points  with a dial gage. It still doesn't account for the mass component (which will vary at different frequencies), but it's the best I have been able to come up with so far.

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3 hours ago, Trenchworker said:

a better idea seems to me to use the Weisshar-Shipman dimensions for a 4/4 violin bass bar thickness of 5.5-6 mm and 13 mm bar height measured from inside at center...

Going purely on dimensions assumes you use wood with a specific set of properties (which never seems to be specified).  It can vary a lot; 50% difference in modulus isn't out of the question.  I check the bass bar weight, which helps, as modulus is strongly correlated with density (but I also know beforehand the modulus of the wood I'm using).

2 hours ago, David Burgess said:

I go through a rather convoluted and time-consuming process of stiffness measurements.Various weights applied to the top and back on a jig, and deflection measured at various points  with a dial gage. It still doesn't account for the mass component (which will vary at different frequencies), but it's the best I have been able to come up with so far.

Is this primarily to get as much consistency in construction parameters as possible, or is there a specific set of measurements that are known to be "best" and deviations from that are not as good?

I too measure absolute plate stiffness, but as yet haven't noticed much correlation between the stiffness measurements and what the instrument does, as long as things aren't too strange (like slab tops, firewood, and 8.5mm arch tops).  As with taptones, free-plate stiffness measurements won't correspond all that well with what happens once you glue the instrument together and put in a soundpost.  Maybe that's the kind of jig you're using; I thought about it, but gave it up as too convoluted and time-consuming, and I wasn't too convinced it would do anything for me.  So I just go with the easy measurements.

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There's an interesting article from Joe Curtin from a 2005 issue of Strad Magazine where he talks about bassbars.  Couldn't find a link in a brief search, but here are the most notable comments paraphrased:

He chooses bassbars that are low density and/or high radiation ratio, which maximizes stiffness to weight ratio.

He starts out with a bar at 14.5mm high and tapered quite a bit thinner at the top than I think is conventional (you'll have to see the photos to get it).  The idea (as I understand it) is that height adds more stiffness than weight and width adds more weight than stiffness.  A bar should be as light as possible for the desired stiffness.

He makes a final adjustment to the bar, based on tap tones which usually brings it to about 14mm. The bar will usually bring his Mode 5 from 310Hz to about 370Hz.  They typically weigh 3-3.5g
 

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2 hours ago, Don Noon said:

As with taptones, free-plate stiffness measurements won't correspond all that well with what happens once you glue the instrument together and put in a soundpost.  Maybe that's the kind of jig you're using; I thought about it, but gave it up as too convoluted and time-consuming, and I wasn't too convinced it would do anything for me.  So I just go with the easy measurements.

Don, I know free plate tap tones don't correlate well to the assembled instrument (I do wonder if rib stiffness is the primary unaccounted for variable there), but doesn't a measurement of M5 with and without the bass bar have some relevance because it is one component that will not vary so much?  I'd love to be able to quantify the bar stiffness in some way.  It doesn't make a lot of sense to me to just stick to a height measurement, since density and stiffness varies (as you mentioned) and I may want a bar more or less stiff depending on the characteristics of a top.  

5 hours ago, David Burgess said:

I go through a rather convoluted and time-consuming process of stiffness measurements.Various weights applied to the top and back on a jig, and deflection measured at various points  with a dial gage. It still doesn't account for the mass component (which will vary at different frequencies), but it's the best I have been able to come up with so far.

David, I'd love to know more about your process.  I've yet to find a meaningful way to quantify bar stiffness objectively, but it seems important.  Anything better than flex and feel is at least a step in the direction that may lead to more consistency and control (in theory).

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