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M2 and soundpost location


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I had a thought today about the M2 and M5 relationship that has led me off on a tangent.  I sketched an approximation of the M2 and M5 nodal lines on the top of the violin that I'm graduating.  M2 passed right through the center of the post location that I had laid out.  I tried to tap and listen for the flex point to verify it, and it seems about right.  It made me wonder whether any study has shown whether there is a benefit to having the soundpost location end up directly on the M2 nodal line.  It makes intuitive sense, but my intuition doesn't always apply well to violin physics.  I'm thinking that top M5 pushes down on post and into back M2 and vice versa, which may complement B1 and B-1 if there's synchrony with that node?

 

Has anyone seen a study that relates to this question?

 

I'm tempted to mark the node on the plates before assembly by setting up a tone generator, then check it again when assembled (perhaps with dust or seeds inside?) to see if it's still in the same place and whether it's under the post.  I have no idea how much the location of this node varies, but I would assume it is a function of arch and graduation.  If you follow a successful pattern it probably ends up in more or less the same spot, but you could probably move it somewhat while graduating.  Even if I checked this, and determined that it did end up under the post I have no idea how I would assess whether there's any benefit to it.  

 

Thoughts anyone?

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Has anyone seen a study that relates to this question?

 

I'm tempted to mark the node on the plates before assembly by setting up a tone generator, then check it again when assembled (perhaps with dust or seeds inside?) to see if it's still in the same place and whether it's under the post.  I have no idea how much the location of this node varies, but I would assume it is a function of arch and graduation.  If you follow a successful pattern it probably ends up in more or less the same spot, but you could probably move it somewhat while graduating.  Even if I checked this, and determined that it did end up under the post I have no idea how I would assess whether there's any benefit to it.  

 

Thoughts anyone?

I have done a modal analysis of a free top and the assembled fiddle box and the top plate movement of the B1- mode was quite similar in shape regarding the nodal line. But the free plate ends are moving a lot more than the block end of the assembled violin box B1- mode, which makes sense. M2 of the free plate and B1- of the assembled violin are not the same modes. But there are some similarities in the nodal lines in the top plates there. 

 

I would guess that the SP position will be close to the nodal line for B1- and it will mainly be driven by the left bridge foot. I do not know if it is better or worse to have the nodal line more inwards or outwards. I would guess that the SP position might influence the position of the nodal line for the B1- mode to some extent. 

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Waste of time.  M2 and M5 cease to exist once you glue the plates to the ribs and put in the soundpost.  

 

I thought Bissinger established in "Surprising regularity between plate modes 2 and 5 and the B1 corpus modes" that there is a correlation between these modes, but the rib stiffness plays a greater role in shaping B1 and B1- modes than M2 and M5.  I understand that M2 and M5 no longer operate in exactly the same way or at the same frequencies, but wouldn't the nodal lines will be similar to those in B1 and B1- since they are the natural flex points of the plates?  I'm really only asking about the nodal line as the natural flex point, not expecting any sort of frequency matching to hold significance once it's assembled.  Are you saying that the nodal lines may appear similar, but there is not the sort of correlation that one might expect?  What is your take on Bissinger's findings?

 

I have done a modal analysis of a free top and the assembled fiddle box and the top plate movement of the B1- mode was quite similar in shape regarding the nodal line. But the free plate ends are moving a lot more than the block end of the assembled violin box B1- mode, which makes sense. M2 of the free plate and B1- of the assembled violin are not the same modes. But there are some similarities in the nodal lines in the top plates there. 

 

I would guess that the SP position will be close to the nodal line for B1- and it will mainly be driven by the left bridge foot. I do not know if it is better or worse to have the nodal line more inwards or outwards. I would guess that the SP position might influence the position of the nodal line for the B1- mode to some extent. 

 

I could see how the soundpost and bridge positions would influence B1 and B1- nodal lines, so perhaps it doesn't even matter.  I imagine you could find those lines without a post and bridge and see where they lie, then see how they change with setup.  I thought that the top M2 and the back M5 nodal lines flex opposite eachother and vice versa as part of the B1 and B1- modes.  I'm just talking about the places where they flex primarily.

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I thought Bissinger established in "Surprising regularity between plate modes 2 and 5 and the B1 corpus modes" that there is a correlation between these modes, but the rib stiffness plays a greater role in shaping B1 and B1- modes than M2 and M5.  I understand that M2 and M5 no longer operate in exactly the same way or at the same frequencies, but wouldn't the nodal lines will be similar to those in B1 and B1- since they are the natural flex points of the plates?

 

Yes, there is a correlation... stiffer plates = stiffer violin body.  And the nodal lines are vaguely similar-looking-ish.  

 

I would take some issue with "natural flex points of the plates, though.  It's just where the plates happen to flex in the two defined edge constraint conditions.

 

And for body modes, the soundpost is in integral structural member which defines the body modes.  Move the post, and the nodal lines will move around a bit.

And there is no guideline that says having the post at any nodal line is good or bad.  It is determined by how the player feels about how it works, and it works just fine with the soundpost not on a nodal line.

 

The fact is, that there are whole bunches of nodal lines at different frequencies, and sometimes the soundpost is near or on a line, and sometimes it isn't.  It's all a balancing act to find the best compromise, and optimizing a particular frequency or two wouldn't be the answer necessarily.

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Yes, there is a correlation... stiffer plates = stiffer violin body.  And the nodal lines are vaguely similar-looking-ish.  

 

I would take some issue with "natural flex points of the plates, though.  It's just where the plates happen to flex in the two defined edge constraint conditions.

 

And for body modes, the soundpost is in integral structural member which defines the body modes.  Move the post, and the nodal lines will move around a bit.

And there is no guideline that says having the post at any nodal line is good or bad.  It is determined by how the player feels about how it works, and it works just fine with the soundpost not on a nodal line.

 

The fact is, that there are whole bunches of nodal lines at different frequencies, and sometimes the soundpost is near or on a line, and sometimes it isn't.  It's all a balancing act to find the best compromise, and optimizing a particular frequency or two wouldn't be the answer necessarily.

 

The way I'm thinking about this may be flawed, but I was thinking that having the soundpost at that node might make that area move more freely.  Perhaps increase the amplitude of B1 and B1- (not that it's always a good thing) or just contribute to overall efficiency by helping the post drive the back.  It seems as though there are a few places (afterlength tuning, tailpiece mode matching, fingerboard tuning) where studies have suggested that synchronizing certain vibrations have a benefit.  I haven't tested any of those individually, but they're easy enough to accomplish (and hard enough to test objectively) so I generally take note and make some effort at synchrony when I'm working in those areas.  Certainly the instruments work fine without matching up all these things, but my impression is (even if it is psychoacoustic) that little tweaks in setup can accumulate to result in a significantly more resonant instrument even when those changes are hard to really hear individually.  

 

Given that you have a better grasp on the interactions between the component pieces and their contribution to the whole, and see no reason to investigate the concept I presented, then I'm not inclined to pursue it further.  Like many things, though, I guess I need to work to re-evaluate the way I conceptualize the inner workings.  Thanks for entertaining another dead end notion.

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