Bass bar theory...

[robedney]

There are many on this forum who have a much greater understanding of the movement of the plates than I do. I'm wondering what you think of this perhaps screwball notion:

Because I'm working in carbon fiber I have the opportunity to try some things that would be difficult in wood. For example, I can mess with the bass bar within larger parameters because I'm less dependent on it for structural support.

I've been thinking that an interesting experiment would be to start with a smaller profile than a traditional bar, and then add mass at the ends of the bar. Think a carbon fiber bar with -- perhaps -- a small ball of lead fitted at each end. I'm assuming (perhaps incorrectly) that given the fact that the two ends of the bar are attached to plate areas of differing resistance (due to differing surface area of the lungs vs. the belly) that some rocking probably occurs in the bar, and that more mass out at the ends may serve to amplify this rocking. And, that experimentally moving these little hunks of lead fore and aft along the bar might be a means of tuning it in some way.

I should add that of the instruments I've made so far that bass bar is thinner than traditional wood but more or less traditional in profile. People like these instruments. However, one very accomplished player suggested that he heard "more in the instrument than was getting out". He then suggested that -- in his experience -- that was often related to the bass bar, and that perhaps in a CF violin the bass bar needed to be cut down in profile.

I'd really appreciate any thoughts here -- including wild speculation

[jezzupe]

There are many on this forum who have a much greater understanding of the movement of the plates than I do. I'm wondering what you think of this perhaps screwball notion:

Because I'm working in carbon fiber I have the opportunity to try some things that would be difficult in wood. For example, I can mess with the bass bar within larger parameters because I'm less dependent on it for structural support.

I've been thinking that an interesting experiment would be to start with a smaller profile than a traditional bar, and then add mass at the ends of the bar. Think a carbon fiber bar with -- perhaps -- a small ball of lead fitted at each end. I'm assuming (perhaps incorrectly) that given the fact that the two ends of the bar are attached to plate areas of differing resistance (due to differing surface area of the lungs vs. the belly) that some rocking probably occurs in the bar, and that more mass out at the ends may serve to amplify this rocking. And, that experimentally moving these little hunks of lead fore and aft along the bar might be a means of tuning it in some way.

I should add that of the instruments I've made so far that bass bar is thinner than traditional wood but more or less traditional in profile. People like these instruments. However, one very accomplished player suggested that he heard "more in the instrument than was getting out". He then suggested that -- in his experience -- that was often related to the bass bar, and that perhaps in a CF violin the bass bar needed to be cut down in profile.

I'd really appreciate any thoughts here -- including wild speculation

If I gather what your saying, to me this may add a "nodal pool" where these are located and restrict movement. But with these types of things one never knows intil they try.

[Johnmasters]

There are many on this forum who have a much greater understanding of the movement of the plates than I do. I'm wondering what you think of this perhaps screwball notion:

I'd really appreciate any thoughts here -- including wild speculation

A bassbar has mass, one can vary that and consider it a pure stiffness. A massless beam. Then add masses. My FEA models would be good for experiments to convince one what might happen to the normal modes. Zaret has gone down this road. Conclusions are hard to make.

If you are interested, buy the $100 Student ABAQUS and I will give you models, how to use, and help with the ABAQUS. (If you have the model already, there is almost nothing to learn with the ABAQUS.)

Jezzupe, that is nonsense.

[Wolfjk]

Hi,

Have you tried your CF instruments without a bass bar?

In traditional instruments the bass bar helps the lower strings by increasing the long grain and mass on the bass side of the instrument. Might not a small increase in plate thicknes on the bass side in a CF instrument do the same job?

[robedney]

If I gather what your saying, to me this may add a "nodal pool" where these are located and restrict movement. But with these types of things one never knows intil they try.

Actually, I'm thinking that it might amplify movement. If the bass bar does indeed rock, beyond some measure of initial resistance it might rock more with more weight on the ends of the beam. This is pure speculation -- and very possibly wrong.

[Johnmasters]

Actually, I'm thinking that it might amplify movement. If the bass bar does indeed rock, beyond some measure of initial resistance it might rock more with more weight on the ends of the beam. This is pure speculation -- and very possibly wrong.

Even in the lowest modes, it bends according to the shape of the mode. Maybe it is a mistake to think of the bar as transmitting the rocking motion of the bridge. That is a view from the static standpoint, not much help with the actual states of motion.

[Fellow]

Hi,

Have you tried your CF instruments without a bass bar?

In traditional instruments the bass bar helps the lower strings by increasing the long grain and mass on the bass side of the instrument. Might not a small increase in plate thicknes on the bass side in a CF instrument do the same job?

+++++++++++++

If you don't need a bassbar for support, you do not need a bassbar.

If you don't have a bassbar, you don't need a soundpost. Bassbar and soundpost work

in tandem. CF instrument is completely different. No grains is for you to worry about.

It will not crack neither. I don't know if it is good thing for our luthier business. Let lyndon say

something.

[lvlagneto]

A lesser to no bar makes sense with CF. A post however seems like it might always be needed, to produce the sound that everyone is used to hearing.

Just try it, and let us know the results. I hate speculation threads... oh wait, that's what 90% of this forum is.

[robedney]

A lesser to no bar makes sense with CF. A post however seems like it might always be needed, to produce the sound that everyone is used to hearing.

Just try it, and let us know the results. I hate speculation threads... oh wait, that's what 90% of this forum is.

Hah! So right you are (about the speculation). I think maybe you've got a point. The bass bar may prove to be redundant, but I do agree that if you eliminate the sound post you both stray too far from the violin sound (been there, done that) and you remove an important adjustment point. I've found that if you go sans sound post you lose much of the focus of the mids and highs (although you get a richer low end). I'm guessing that this is because the top and bottom plates are no longer mechanically linked, and the bridge behaves very differently without the post in its vicinity.

So, I'll do that (just try it) and report back. If that proves confusing, I'll maybe take John up on his very kind offer with Abacus, although I'm not sure I'm up for the learning curve. I started this whole project from a theoretical/analytical perspective and ultimately concluded that the empirical approach is not only more direct but -- for me at least -- faster. I seem capable of learning new tricks (in regards to the analytical approach) but lack the sort of background that, for example, John and Don have to fit it all into and make sense of it.

[robedney]

+++++++++++++

If you don't need a bassbar for support, you do not need a bassbar.

If you don't have a bassbar, you don't need a soundpost. Bassbar and soundpost work

in tandem. CF instrument is completely different. No grains is for you to worry about.

It will not crack neither. I don't know if it is good thing for our luthier business. Let lyndon say

something.

I wouldn't worry about the luthier business -- carbon fiber is unlikely to replace wood in large numbers. Moreover, it I start to sell these things -- instead of just investing in them -- I'll have more expendable income, and the most likely expenditures will be on wooden instruments from contemporary American makers I'd like to own (and Manfio, of course). Edit: I think I need to include the Aussies in that too -- and maybe the Brits. You can see where this is going...

[Johnmasters]

I wouldn't worry about the luthier business -- carbon fiber is unlikely to replace wood in large numbers. Moreover, it I start to sell these things -- instead of just investing in them -- I'll have more expendable income, and the most likely expenditures will be on wooden instruments from contemporary American makers I'd like to own (and Manfio, of course). Edit: I think I need to include the Aussies in that too -- and maybe the Brits. You can see where this is going...

The worst speculation is that the sounpost means more than the bassbar. They are both impedance couplings to the violin.

[lvlagneto]

I wasn't trying to imply that a bass bar is redundant, but that you will probably be able to get the same effect in CF with a bar that is not the same dimensions as a wooden one (perhaps something as subtle as an adjustment in weave/thickness.

I do think that in the case of CF, where structurally you could go without a post or bar support of any kind, the post seems more important in keeping the sound traditional (going through the back and top). Other adjustments could be made to get what one would expect on the bass side without a full bar... but I'm speculating, just like everyone else.

[Johnmasters]

I wasn't trying to imply that a bass bar is redundant, but that you will probably be able to get the same effect in CF with a bar that is not the same dimensions as a wooden one (perhaps something as subtle as an adjustment in weave/thickness.

I do think that in the case of CF, where structurally you could go without a post or bar support of any kind, the post seems more important in keeping the sound traditional (going through the back and top). Other adjustments could be made to get what one would expect on the bass side without a full bar... but I'm speculating, just like everyone else.

Well, I am not speculating. The bar is a piece of stiffness many times stiffer in proportion to its mass than any other part of the body. One could speak of a very low mass web normal to the inside surface. That would make sense. One would not have to worry about too low mass. But if you give up the stiffness in favor of more mass, that is the opposite way to go.

[Torbjörn Zethelius]

For a strong player a stronger bassbar is probably needed even in a CF violin. Just my guess. How thick are your plates?

[David Hart]

while we're speculating, would it be possible to, instead of a bass-bar, incorperate something into the CF violin with which you could alter the stiffness? Like some type of wire threaded through an object, as is done in modern bridges. As I know, the steel wires threaded through pre-constructed bridges are designed to be able to alter the tension in the bridge. My high school engineering is a little fuzzy, but doesn't that alter the stiffness? You could have say some sort of bass bar set-up, with a steel wire threaded through, with both ends protruding on the outside of the instrument attatched to some sort of device to alter the tension in the cable.

This could work, right? Or am I going over people's heads?

EDIT:

Actually i have a better idea. make the bass bar normal length, but instead of the usual shape, make the curve round. make a groove along the bottom of the bassbar, punch holes in the top at the ends and run a threaded cable through (ask wittner to make a really long cello tailgut?) then use those threaded things for turning stuff you find on clamps (BRAINFREEZE) to tighten the ends. you can also use washers so they don't dig into the CF.

EDITX2:

Maybe I should be the one making carbon fiber violins!

[David Burgess]

I think Benoit Rolland did something like this with his "Spiccato" line of adjustable stiffness bows.

[David Hart]

That would make sense, although it would probably be rather awkward having to change bows JUST to play spiccato!

[apartmentluthier]

A bassbar has mass, one can vary that and consider it a pure stiffness. A massless beam. Then add masses. My FEA models would be good for experiments to convince one what might happen to the normal modes. Zaret has gone down this road. Conclusions are hard to make.

John,

Is it the mass or the stiffness that is the secret sauce? The Zarret bar adds mass, but is it the added mass that is "perceived" to work, or the added stiffness?

[Johnmasters]

Actually i have a better idea. make the bass bar normal length, but instead of the usual shape, make the curve round. make a groove along the bottom of the bassbar, punch holes in the top at the ends and run a threaded cable through (ask wittner to make a really long cello tailgut?) then use those threaded things for turning stuff you find on clamps (BRAINFREEZE) to tighten the ends. you can also use washers so they don't dig into the CF.

Adjusting that tension is not the same as adding stiffness. If you stay in the linear region of the elastic properties of the wire, the spring constant (stretch per pull) would not change. It would only change the preload on the bar. Adjusting the height of the bar truly makes it stiffer.

Note: Tension on the strings raises the frequency for a different reason. (The way it opperates geometrically in the equations is different.) I don't know about the spicatto bow...

John,

Is it the mass or the stiffness that is the secret sauce? The Zarret bar adds mass, but is it the added mass that is "perceived" to work, or the added stiffness?

A tall beam has stiffness grow faster than mass. You can take a floor joist and lay it flat. It would have the same mass but much less stiffness. That will tell you what is needed. If a CF violin had a very thin web, I think it would act like the stiffness it should be. If it has too little mass, that might change the tone (perhaps to brighter) but would be a lot better than adding a line of mass down that position.

We are used to a wooden bassbar, so all the results of graduation are worked out with that in mind. If the bassbar were (say) a web of aluminum in a wooden violin, then perhaps it would work well with small changes in graduation. (I once thought to try this on a lark, but then never did it.)

I believe that Peter Zaret's father was an engineer in some field. I recall this from something I read. The idea came from him, or thorugh him to his son. Mass distribution along with stiffness seems to be what is being tried with those bars. I have even seen three seperate blocks. So the stiffness is interrupted. There is some trial and error going on there. But in the end, it is stiffness that is needed. Extra mass might be added to tone down a harsh violin, perhaps. There is no single Zaret bassbar, or at least was not when I saw more than one kind a few years ago.

[robedney]

OK, after pondering overnight and reading the additions above, I'm thinking that step one (working experimentally) is to significantly lower the profile of the existing bar in a prototype. Thanks for the floor joist example John, that helped me with the mass vs. stiffness issue.

I have one prototype with a zip off top (it's glued on with black high temp silicone). It also happens to be the variation with the thinnest plates. So, I can record some open strings and spectral analysis before, then again after re-profiling the bar. That ought to demonstrate something.

One thing that's occurred to me is that it's easy to put mass back if needed, so I'll judge the new profile based on my sense of how the plate handles loading on the bass side and take it down as far as I'm comfortable with.

[Johnmasters]

OK, after pondering overnight and reading the additions above, I'm thinking that step one (working experimentally) is to significantly lower the profile of the existing bar in a prototype. Thanks for the floor joist example John, that helped me with the mass vs. stiffness issue.

I have one prototype with a zip off top (it's glued on with black high temp silicone). It also happens to be the variation with the thinnest plates. So, I can record some open strings and spectral analysis before, then again after re-profiling the bar. That ought to demonstrate something.

One thing that's occurred to me is that it's easy to put mass back if needed, so I'll judge the new profile based on my sense of how the plate handles loading on the bass side and take it down as far as I'm comfortable with.

Maybe if you took a conventional violin and put a dial gauge on the top and squeezed at the left bridge foot. You could make your CF violin have a similar springiness. Yes, you could adjust all the springiness and then add mass later. The CF has a lot of strength per mass, so it makes sense to find the desired stiffnesses first. At least to me. And if you want to add damping, paint the inside with a coat of the stuff they spray on the insides of car doors.

[robedney]

Maybe if you took a conventional violin and put a dial gauge on the top and squeezed at the left bridge foot. You could make your CF violin have a similar springiness. Yes, you could adjust all the springiness and then add mass later. The CF has a lot of strength per mass, so it makes sense to find the desired stiffnesses first. At least to me. And if you want to add damping, paint the inside with a coat of the stuff they spray on the insides of car doors.

I can do that (measuring and adjusting the resistance in the area of the bass bar) -- good thought.

I've had the same thought (as you, above) about adding damping. My latest prototype is somewhat thicker with more mass. I was looking for a more focused sound, and I thought it worked. The pros I've had play the two I'm working with at the moment like the thinner, lighter instrument better, in fact asking me to make something as thin and light as possible to try on the next round. They felt I was pretty darned close with the lighter instrument. I'm listening to them.

So, I'm back to where I was at one point -- building as light as I can while still producing a highly durable instrument -- and adding damping if and where needed. I'm moving my shop right now to gain space. As soon as I'm done with that I'm going to work on the next one. I'm going to take some time while doing that to develop some version of an adjustable post, and perhaps a CF bridge. I'm a little reluctant to take on the bridge right now because it is such a critical component and there is so much territory to explore. We'll see.

John, I will definitely send you the next one to have a look at (once I've gotten some feedback from the aforementioned pros).

[Johnmasters]

I can do that (measuring and adjusting the resistance in the area of the bass bar) -- good thought.

I've had the same thought (as you, above) about adding damping. My latest prototype is somewhat thicker with more mass. I was looking for a more focused sound, and I thought it worked. The pros I've had play the two I'm working with at the moment like the thinner, lighter instrument better, in fact asking me to make something as thin and light as possible to try on the next round. They felt I was pretty darned close with the lighter instrument. I'm listening to them.

So, I'm back to where I was at one point -- building as light as I can while still producing a highly durable instrument -- and adding damping if and where needed. I'm moving my shop right now to gain space. As soon as I'm done with that I'm going to work on the next one. I'm going to take some time while doing that to develop some version of an adjustable post, and perhaps a CF bridge. I'm a little reluctant to take on the bridge right now because it is such a critical component and there is so much territory to explore. We'll see.

John, I will definitely send you the next one to have a look at (once I've gotten some feedback from the aforementioned pros).

I am certainly curious. Problem is people often do not know exactly what they want. Many are inclined to play for a few seconds and discard it. I thought it was telling when a few days ago someone mentioned that it took so-and-so three years to play his certain Strad. Too bad you will not find someone to give your violins an honest try for three years.

Make it open and full. If it is not harsh or grating, I am sure it will be what many people want.