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Does the soundpost bend? https://youtu.be/m3cgG-TJs9Q


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2 hours ago, James M. Jones said:

The video is really showing compression not really bending 

Looks like bending to me.

If you push on the side of the soundpost with a feather, the post will bend.  It's all a matter of degree.  While I can't independently verify that the video is accurate, I see no obvious problem with it.

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On 1/25/2023 at 10:43 AM, Don Noon said:

Looks like bending to me.

If you push on the side of the soundpost with a feather, the post will bend.  It's all a matter of degree.  While I can't independently verify that the video is accurate, I see no obvious problem with it.

Well as usual your very correct

I guess what I was trying to point out , is that what they show , yes it is bending but not in a common sense , that is it’s not observed by the naked eye;

“ it’s moving as they show but extremely exaggerated “

this movement they show is a result of the compression, So yes it bends , but not in a way normal people can measure with common tools . 

Yes , It’s a matter of degree 

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8 hours ago, James M. Jones said:

this movement they show is a result of the compression

I see it as the rocking motion of the top plate causing the bending.  Compression would just make the post shorter, until it buckled (but it's a long way from that).

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On 1/27/2023 at 5:29 PM, Don Noon said:

I see it as the rocking motion of the top plate causing the bending.  Compression would just make the post shorter, until it buckled (but it's a long way from that).

Well yes , the rocking motion of the top like a see saw , sends that pulse that causes the bending action - I agree , simple to see that , I’d expect the inside of the bend across the width of the soundpost to be exerting more pressure than the out side of the bend , that is if we could accurately measure the difference in pressure on the post  from the bass side to treble of the post , at the juncture of the sound post and top or back plate, should I expect to see or do you expect a difference during the rocking of the top.? Or would the pressure remain constant. . 

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This is just a simulation. The programmer decided to allow the sound post to bend. I wonder whether such simulations can be used for any kind of prediction of sound quality. As this comes from Yokoyama Music Lab I would assume that this is the goal.

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Another thing to keep in mind is that the simulation is heavily dependent on how the sound post top and bottom elements are attached to the plate elements. The simple way is to make the elements share common node points, but this links nodal rotations between the sound post ends and the plate surface that do not actually occur. So you can get an exaggerated bending load on the sound post ends.

I have simulated contact surfaces with finite element programs and it is not a simple task. But in this case, the deflections at the sound post ends are so small it is probably good enough to use the simpler setup.

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Hi, Im new here but I believe there are significant modeling issues going on because this is a very very complicated model. 

First, this is very difficult to model as the size and number of the NURBS radically skews the presentation.  The fewer nurbs modeled, the more movement you see in the resultant calculations.  There is also the stiffness of the soundpost as modeled in the movie, it almost appears to have infinite flexibility, and I think that's not correct.  Since the soundpost is held in place with a static compression load, and we know that the soundpost compression loads never get to zero, or they move or fall out, we need to model the action as a sinusoidal load driven from the top plate to the back, through the sound post with vertical movement of the post controlled by the stiffness delta of the top and back and the elasticity of the soundpost.  One can calculate vibratory nodal points of the sound post and I suspect it has no sympathetic vibe nodes.  If I were a betting man, Id bet that the soundpost doesn't bend per se, but as the compression load changes go through the post it locally bulges in a uniform circumferential manner, and depending on the frequency transmitted, possibly more than one bulge and the movements will be very small and darn hard to measure real time

 

Edited by SCorrea
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