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kayjay

Bridge feet thickness

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It has to do with Mass, if the bridge is not up to the mass required to resonate with the string then the energy flows through to fast filtering out the higher frequencies. At least this is what I have observed. The thinner bridges also react to temp, and humidity changes faster causing a change in the way the energy flows through the bridge.

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55 minutes ago, Peter Lynch said:

why would very thin bridges be more likely to filter out very high frequencies (in contrast to thicker bridges)

The reason I said guessing is that I really don't know. Perhaps Don could weigh in on this. I remember an interesting lecture Norm Pickering gave on bridge function and will check my notes when I get a chance.

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Just to throw out an alternate method that I feel has some application. One can thin the feet to 3 and then glue on balsa shoes of 1.5. tiny "shoes" or pieces of balsa, glued on with hide glue, then shaped and filed are generally invisible and can be helpful for fitting to tops that have been chewed up from bad fittings, age or neglect. You may wish to choose a lighter and fluffier piece that is more prone to compressing and thus form fitting over rough areas. 

I like it because it in general seems to make it much harder to start any damage or compression setting of the grain locally under the bridge feet. And to my ears has no ill sonic effects, and may even be beneficial as the balsa will conform better than even the best fit maple foot and has the ability to allow an amateur to get 100% contact with a foot that might not have else-wise, it turns it into more of a horseshoes and hand grenades related to "thickness of paper' widths which are what make the difference in 100% foot contact. 

I too see many pictures of feet that I think are too thin as if it was like they wer trying to make them so thin that they will flex and wrap around contours like "self fitting" bridges. If your not going to get ot perfect at least the balsa allows for 100% contact still, the down force pressure may be askew, but at least there is no gap between the bottom of the foot and the top.

Yes, it is unorthodox, but because it can be a good trick when dealing with a messed up top, anywhere from gouged out wood, to abusive rosin build up.

I dealt with a fiddler awhile back who must have thought the "magic" came from the rosin build up, because obviously cleaning it off periodically wasn't in the program. 

When the tension was off, the bridge stood there glued in place by the caked on rosin and came of with a "snapping" sound. Anyways, cleaned it up only good enough to get contact as cleaning the fiddle would have been a 1 day job in itself, and he didn't want much of the "magic" removed if possible. This would have been nearly impossible to fit based on the messed up area of the general bridge location, so I  picked a very "foamy' piece of balsa, accounting for some height loss due to compression and it fit great, right over all that crud., which of course wasn't huge, but certainly wasn't like a newish unmolested top.

.

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Do you account for the bridge foot thickness when adding these shoes?

how quickly should a foot taper down to 0.75mm?

This is what I aim for at the moment (please excuse the low resolution and the bumps in the cut). Is this about right?

B3E924DA-B51F-40A4-A187-CFF9C4132919.thumb.jpeg.dbb3d7c6da02ca264c238f49deab7340.jpeg

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17 minutes ago, Andreas Preuss said:

How strict do you follow measurements, would be a question I'd be more interested in.

For foot thickness, very strict. Top thickness, a little less so, and the rest we do by feel.  The thickness does not make much difference in the flexibility compared to the width of the given elements.  Flexing from the two sides down in a rocking motion allows us to feel a great deal.....after all flexibility is the element I am trying to control.  It takes the strength of the blank, the depth of the cut, the quality of the wood, the bridge height, and the poiriette all into account by a quick action.  It also allows us a basis to check old bridges in comparison.

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10 hours ago, Peter Lynch said:

why would very thin bridges be more likely to filter out very high frequencies (in contrast to thicker bridges)

Actually I made an experiment with thinning down a bridge but without checking the results on a sound spectrum. 

Si the impression just from comparing with hearing was that  going down from 4.5 to 4.2' would give more edge to the sound, going further down to 4.0 would make the sound sharp -and still further a kind of raspy and on certain notes harder to control.

i can't say however if this works on all violins the same way. My motivation was to find out how much I could alter the sound of my own violins to the demand of customers without doing massive alterations.

 

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27 minutes ago, Michael Darnton said:

Apparently my drawing earlier didn't have an effect on anyone. . . .

Your drawing left out the 3rd option which is to plane the front parallel to the back.  I do not see bridges with either of your options come through the shop that show signs of logical intent or capable craftsmanship. 

Edit: I probably should add that I only recall one of your bridges from long ago that was not fashioned as you described.

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I see. . . .

The drawing was not about final shapes, it was about the initial thinning, and what wood each method left to manipulate in shaping the bridge later. But if no one wants to think that thickness in the central areas might be important to anything, I will leave it at that. Everyone already knows my opinions about acoustical models vs mechanical models, I think.

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8 hours ago, saintjohnbarleycorn said:

is there a standard to the vertical thickness of the bridge foot,  I know its on a curve not flat but at the thinnest point what would be the measurement to shoot for?

thanks 

The vertical thickness can change depending on the top, especially with cello bridges.  For instance, leaving the inside of the foot a little thicker on a Belgium bridge for a high arched instrument for example....of course I would then leave the toes a little thicker as well but I have seen tastefully done Belgium bridges with the inside and the outside of the feet at different thickness’.

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10 hours ago, Michael Darnton said:

I see. . . .

The drawing was not about final shapes, it was about the initial thinning, and what wood each method left to manipulate in shaping the bridge later. But if no one wants to think that thickness in the central areas might be important to anything, I will leave it at that. Everyone already knows my opinions about acoustical models vs mechanical models, I think.

 

 

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22 hours ago, nathan slobodkin said:

The reason I said guessing is that I really don't know. Perhaps Don could weigh in on this. I remember an interesting lecture Norm Pickering gave on bridge function and will check my notes when I get a chance.

 

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I would be interested on any thoughts about bridge function from reliable sources.

Also, is it truly correct to say a bridge filters?   I have heard that so many times but am skeptical when I see a word used so frequently. 

I guess if a thick bridge is filtering high frequencies as I so often heard...

Would it be logical to infer that a thin bridge filters low frequencies? 

In fact, a thinner bridge should flex more.  Promoting Longer wavelengths.  Lower sounds.  Mechanically it would seem that a thin bridge should promote a deeper sound. 

A thicker bridge would flex less, promoting smaller vibrations, promoting higher sounds.  

This makes me question the convenient term "filter".

I'm full of questions and full of ignorance.  School me.

 

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I tend to agree, filtering is not the correct term, I think focus would be better term. If you look at Jerry's avatar picture, you can see the bridge center is shaped like a Heart.  This shape acts like a venture nozzle, by compressing the vibrations from the strings and focusing them toward the bridge feet. I also use this method om my instruments.

 

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3 hours ago, Fiddlemaker5224 said:

If you look at Jerry's avatar picture, you can see the bridge center is shaped like a Heart.  This shape acts like a venture nozzle, by compressing the vibrations from the strings and focusing them toward the bridge feet. 

 

This analogy hurts my head.  I’d like to ask you to elaborate...

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On 4/21/2019 at 3:06 PM, Jerry Pasewicz said:

Yes, that is what we do.

BTW, your bridge carving instruction is one of the most detailed, comprehensive and informative i've come across until now. 

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