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kayjay

Bridge feet thickness

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12 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. I also use this method om my instruments.

 

But the heart on Jerry's bridge is sideways, so it is obviously intended to funnel the sound toward either the bass or treble side.

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1 hour ago, Michael Szyper said:

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

Thank you, I will pass that on to the authors.  I have been very lucky to work with some very good people.

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13 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. I also use this method om my instruments.

 

Are you serious?

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2 hours ago, Michael Szyper said:

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

Same! It is possibly my main article when referring to bridge carving, so many thanks 

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On 4/22/2019 at 7:21 AM, Michael Darnton said:

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

Yes it did, I have thought long about this since you told me about it on MIMF.

On 4/22/2019 at 8:43 AM, 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.

I still make adjustments to the thickness of the center depending on the density of the bridge and its tap tone.

14 hours ago, Mnorfleet said:

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

OK

3 hours ago, arglebargle said:

Are you serious?

Yes, His avatar is sideways :) imagine it rotated 90 degrees clockwise.

86598050_190Figure25fbridge.jpg.44b0afb4d2cd6a848523f3f6de700248.jpg

Choked flow

The limiting case of the Venturi effect is when a pressure wave reaches a state of choked flow, where the pressure wave velocity approaches the local speed of sound. When a pressure wave is in a state of choked flow, its density is increased. A further decrease in the downstream pressure environment (thickness of the Arm) will not lead to an increase in the flow rate. However, flow rate for a pressure wave will increase with increased upstream pressure (Bow Pressure), which will increase the density of the pressure wave through the constriction (though the velocity will remain constant) imparting added energy.  At the exit of the Arm toward the feet increases the local sonic velocity, thus allowing for increased pressure wave flow rate but only if the nozzle area is also increased to compensate for the resulting decrease in density. Leaving the center of the bridge below the Eye the same thickness as the feet allows this pressure wave to expand with added energy to the bridge feet. Imparting increased energy to the top of the instrument through the bridge feet. Controlling the flow of the energy wave through the various sections of the bridge helps to control the pressure wave (vibration) imparted to the top of the instrument. Adding the heart shape to the Eye increases the density of the pressure wave through the Arm. Delivering the increased energy to the bridge feet. The shaded areas on the drawing are areas that are used to focus and redirect the pressure wave. Some experimentation will be needed as each bridge is different and will require tuning for the density of that bridge. Please give my theory a try for yourself.

 

 

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23 minutes ago, Fiddlemaker5224 said:

Yes it did, I have thought long about this since you told me about it on MIMF.

I still make adjustments to the thickness of the center depending on the density of the bridge and its tap tone.

OK

Yes, His avatar is sideways :) imagine it rotated 90 degrees clockwise.

86598050_190Figure25fbridge.jpg.44b0afb4d2cd6a848523f3f6de700248.jpg

 

 

 

I think the bridge on Jerry's avatar is a French style 'cello bridge...  The great majority of French 'cello bridge blanks have a heart shaped with the point.  Jerry makes them look classier though.

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10 hours ago, Fiddlemaker5224 said:

Yes it did, I have thought long about this since you told me about it on MIMF.

I still make adjustments to the thickness of the center depending on the density of the bridge and its tap tone.

OK

Yes, His avatar is sideways :) imagine it rotated 90 degrees clockwise.

86598050_190Figure25fbridge.jpg.44b0afb4d2cd6a848523f3f6de700248.jpg

 

 

Choked flow

 

The limiting case of the Venturi effect is when a pressure wave reaches a state of choked flow, where the pressure wave velocity approaches the local speed of sound. When a pressure wave is in a state of choked flow, its density is increased. A further decrease in the downstream pressure environment (thickness of the Arm) will not lead to an increase in the flow rate. However, flow rate for a pressure wave will increase with increased upstream pressure (Bow Pressure), which will increase the density of the pressure wave through the constriction (though the velocity will remain constant) imparting added energy.  At the exit of the Arm toward the feet increases the local sonic velocity, thus allowing for increased pressure wave flow rate but only if the nozzle area is also increased to compensate for the resulting decrease in density. Leaving the center of the bridge below the Eye the same thickness as the feet allows this pressure wave to expand with added energy to the bridge feet. Imparting increased energy to the top of the instrument through the bridge feet. Controlling the flow of the energy wave through the various sections of the bridge helps to control the pressure wave (vibration) imparted to the top of the instrument. Adding the heart shape to the Eye increases the density of the pressure wave through the Arm. Delivering the increased energy to the bridge feet. The shaded areas on the drawing are areas that are used to focus and redirect the pressure wave. Some experimentation will be needed as each bridge is different and will require tuning for the density of that bridge. Please give my theory a try for yourself.

 

 

 

 

Sure....as soon as I understand what you just wrote.  I am not writing it off, it is interesting, and I will give a serious look, but that is not what I was thinking when I cut the bridge....at least I do not think that is what I was thinking.

Jeff is correct, it is a cello bridge.  I am not sure your hypothesis doesn’t still apply...at least I do not think I am sure.....maybe I am sure...

In any case thanks for this.

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14 hours ago, Fiddlemaker5224 said:

 

86598050_190Figure25fbridge.jpg.44b0afb4d2cd6a848523f3f6de700248.jpg

 

How do you measure the waves traveling through the bridge? Based on your drawing it seems like the A and D string waves would hit the upper part of the heart and bounce back, barely reaching the feet.  My understanding is that the vibrations moving through the bridge are a lot more complex than what you illustrated. If the heart was upside down, would the sound be effected? What if it was a circle? Honest questions.

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Checking my notes on the Pickering lecture (VSA 1988?) Norman referred to the bridge as a "high pass filter". I didn't understand it then and still don't so if any one can explain that I'm all ears.

As regards Venturi effects of vibrations in wood. I am familiar with the increased velocity of fluids moving through a funnel but don't believe vibrations in a solid would act the same way. Again, way past my level of scientific education.

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3 hours ago, arglebargle said:

How do you measure the waves traveling through the bridge? Based on your drawing it seems like the A and D string waves would hit the upper part of the heart and bounce back, barely reaching the feet.  My understanding is that the vibrations moving through the bridge are a lot more complex than what you illustrated. If the heart was upside down, would the sound be effected? What if it was a circle? Honest questions.

Currently I do not have a reliable way of measuring this. When a pressure wave encounters an object that object is set in motion creating vibrations of its own. When the object is shaped like a funnel it acts to concentrate the pressure wave. Thereby causing an increase in energy at the choke point ( thinnest cross section of the arm). Then is regulated at the speed of sound as it passes to the legs. I simplified the drawing of the pressure wave for a better representation. The energy is directed to the feet of the bridge through the legs with a constant speed while having an increased energy output.

2 hours ago, nathan slobodkin said:

Checking my notes on the Pickering lecture (VSA 1988?) Norman referred to the bridge as a "high pass filter". I didn't understand it then and still don't so if any one can explain that I'm all ears.

As regards Venturi effects of vibrations in wood. I am familiar with the increased velocity of fluids moving through a funnel but don't believe vibrations in a solid would act the same way. Again, way past my level of scientific education.

As I understand the function of the bridge, the above described behavior, is present in all Pressure waves, no matter what medium they are passing through. The bridge is the first vibration filter in all bowed string instruments. The end result is that the instrument is excited through these vibrations creating new pressure waves in the air around the instrument that propagates outward. This occurs in any medium, and we sense this pressure wave as sound because the medium we are manipulating is the air we breath..

Yes I too am still trying to figure this out. Sometimes I feel like pulling out the remaining hair I have left. Always in search of obtaining better sound.

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7 hours ago, Jerry Pasewicz said:

Sure....as soon as I understand what you just wrote.  I am not writing it off, it is interesting, and I will give a serious look, but that is not what I was thinking when I cut the bridge....at least I do not think that is what I was thinking.

Jeff is correct, it is a cello bridge.  I am not sure your hypothesis doesn’t still apply...at least I do not think I am sure.....maybe I am sure...

In any case thanks for this.

I believe it does, also I think you have the instinctive thought to cut the cello bridge as you do. My question to you is what changes in tone did you hear? Did you use a wood end pin instead of the metal tubes or Rods that support the cello during playing? If yes, did this give you a better tone>

Thanks for the input.

 

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4 minutes ago, Fiddlemaker5224 said:

I believe it does, also I think you have the instinctive thought to cut the cello bridge as you do.

Thank you for the compliment, but unless we are now referring to Burgess’ and Morel’s prodding as “instinctive thought”, I think it was training and practice.

4 minutes ago, Fiddlemaker5224 said:

My question to you is what changes in tone did you hear?

This will take some time, but I am not sure the changes I hear are based on the theory.  I am not saying they do not, just that it will take time to think about.

4 minutes ago, Fiddlemaker5224 said:

 

Did you use a wood end pin instead of the metal tubes or Rods that support the cello during playing? If yes, did this give you a better tone>

Thanks for the input.

 

I have never been able to predict which endpin will sound better with any given cello.

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1 hour ago, Fiddlemaker5224 said:

Currently I do not have a reliable way of measuring this. When a pressure wave encounters an object that object is set in motion creating vibrations of its own. When the object is shaped like a funnel it acts to concentrate the pressure wave. Thereby causing an increase in energy at the choke point ( thinnest cross section of the arm). Then is regulated at the speed of sound as it passes to the legs. I simplified the drawing of the pressure wave for a better representation. The energy is directed to the feet of the bridge through the legs with a constant speed while having an increased energy output.

 

So the image you presented is just your speculation of how a bridge vibrates? I don't see the bridge as funnel shaped at all, or any aspect of it either. The "heart" is the consequence of the aesthetic sensibilities of the time, not some kind of vibration-directing device.

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2 hours ago, arglebargle said:

In fact, if it was the case you describe, than wouldn't this would be the more effective design, an older baroque bridge?

teller_violin_bridge_68_baroque.png

I could be wrong in this interpretation, but I think the funnel referred to is when the waves pass from the part of the bridge with more surface area (above the heart) to the constricting parts with less surface area (between the kidney on each side and the heart in the middle, or the legs).  If that interpretation is correct the upside down heart would still create a funnel, maybe more efficiently as you suggested.

 

 

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22 hours ago, Fiddlemaker5224 said:

Yes it did, I have thought long about this since you told me about it on MIMF.

I still make adjustments to the thickness of the center depending on the density of the bridge and its tap tone.

OK

Yes, His avatar is sideways :) imagine it rotated 90 degrees clockwise.

86598050_190Figure25fbridge.jpg.44b0afb4d2cd6a848523f3f6de700248.jpg

 

 

Choked flow

 

The limiting case of the Venturi effect is when a pressure wave reaches a state of choked flow, where the pressure wave velocity approaches the local speed of sound. When a pressure wave is in a state of choked flow, its density is increased. A further decrease in the downstream pressure environment (thickness of the Arm) will not lead to an increase in the flow rate. However, flow rate for a pressure wave will increase with increased upstream pressure (Bow Pressure), which will increase the density of the pressure wave through the constriction (though the velocity will remain constant) imparting added energy.  At the exit of the Arm toward the feet increases the local sonic velocity, thus allowing for increased pressure wave flow rate but only if the nozzle area is also increased to compensate for the resulting decrease in density. Leaving the center of the bridge below the Eye the same thickness as the feet allows this pressure wave to expand with added energy to the bridge feet. Imparting increased energy to the top of the instrument through the bridge feet. Controlling the flow of the energy wave through the various sections of the bridge helps to control the pressure wave (vibration) imparted to the top of the instrument. Adding the heart shape to the Eye increases the density of the pressure wave through the Arm. Delivering the increased energy to the bridge feet. The shaded areas on the drawing are areas that are used to focus and redirect the pressure wave. Some experimentation will be needed as each bridge is different and will require tuning for the density of that bridge. Please give my theory a try for yourself.

I'm not seeing what you have represented as being anywhere close to the actual vibrating modes of bridges, which have been quite well studied.

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4 hours ago, arglebargle said:

In fact, if it was the case you describe, than wouldn't this would be the more effective design, an older baroque bridge?

teller_violin_bridge_68_baroque.png

It probably was for gut strings, now that string types have changed. The bridge is also evolving. The main problem I see with the above bridge is that there is not enough mass in the legs through the arms. Perhaps I will have to try that design. Thanks for the idea.

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1 hour ago, David Burgess said:

I'm not seeing what you have represented as being anywhere close to the actual vibrating modes of bridges, which have been quite well studied.

As previously stated, I simplified the wave representation to get my Idea across.

Do you have a reference for the studies you mentioned?

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4 hours ago, arglebargle said:

So the image you presented is just your speculation of how a bridge vibrates? I don't see the bridge as funnel shaped at all, or any aspect of it either. The "heart" is the consequence of the aesthetic sensibilities of the time, not some kind of vibration-directing device.

If it as you say Speculation, then how do the vibrations reach the feet. The Wave representation  is just showing the flow path the pressure waves take through the bridge. Not the vibrating modes of the bridge itself.

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4 hours ago, arglebargle said:

So the image you presented is just your speculation of how a bridge vibrates? I don't see the bridge as funnel shaped at all, or any aspect of it either. The "heart" is the consequence of the aesthetic sensibilities of the time, not some kind of vibration-directing device.

Argle,

I don't think the complex shape of the bridge is just for looks . The standard shape and that of cello bridges as well, allows no direct transmission of vibration between any string and the top of the instrument. All vibrations have to involve the whole bridge.

David- Any references to some of the studies on bridge vibration? Didn't that Icelandic violin maker (Johannsen?) do quite a bit on this?

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So reading the article David posted I don't understand if the preferred vibration frequencys of the bridge are transmitted to the top of the instrument making those frequencies  louder or If the vibration  of the bridge means that energy is used up moving the bridge in those frequencies and thus reducing their contribution to the motion of the top.

Also as usual we have the paradox that while lowering the mass of the bridge should raise it's frequency that is negated or surpassed by the loss of stiffness which lowers the resonant frequency.

i've been cutting bridges for years according to directions like "cut here to make the sound more open" but really have no idea of what is happening in terms of the physics.

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A high pass filter means that high frequencies are transmitted (passed through), but low frequencies are stopped. Usually, there is a cutoff frequency. Below this point low frequencies are stopped. Above it the high frequencies pass.

Disclaimer: I have to check Norm Pickering's book, but I think he was referring to the slip-stick action of the rosined bow hair that produces a wide range of frequencies. 

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Yes, Nathan, when I read the article I had several thoughts. One was that every cut seemed to lower the frequencies away from what I thought people had decided was ideal, so why would you do that. The other thought was that what he did doesn't relate much to how I cut a bridge, anyway. The final thought was that I seem to be doing fine without this information. :-) 

 

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