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integral bass bar


nathan slobodkin
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2 hours ago, Anders Buen said:

No, but not far from. The tangential direction is about half the radial, while both are 5-13% ish of the longitudinal. So for all practical means, quite similar. The twisting modulus is also close to the radial modulus for spruce. Of course, there are variations from piece to piece.

i think the bending stiffnes goes as the modulusˆ1/2 so the numers does not need to be very precise for practical assessments.

Bending stiffness is proportional to elastic modulus (^1) not the square root (^1/2).

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14 hours ago, Don Noon said:

A factor of 2 is considerable.  Having made a slab-top violin, I can attest to the lowering effect on the taptones.  However, in the assembled instrument, the stiffness of the back and longitudinal stiffness of the top make the floppy crossgrain top not so important.  The B mode frequencies were only slightly low, and it sounded and played well.  Not a screamer, though.

Slabcut backs seem to give low B1+ mode frequencies. I think the low crossgrain stiffness of the top play a significant role in violin acoustics and performance. The arching should give smaller effects from the E-modules on the main mode frequencies than for a flat plate, at least so for mode 5. The crossgrain stiffness fall fast when the ring angle is off 90 degrees. And it is quite possible to get crossgrain stiffnesses lower than the general tangential stiffness of spruce may give alone.

Of of the main reasons for not using slabcut spruce is the larger humidity creep and swell in the tangential direction. I think that may be the case for the maple backs too, although the differences probaly are smaller for maple than for spruce.   

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1 hour ago, Anders Buen said:

Of of the main reasons for not using slabcut spruce is the larger humidity creep and swell in the tangential direction.

The main reason for me against slabcut backs is the cracking issue from reduced strength and higher shrinkage.  For tops, yikes.  Bass bars don't have big issues with any of this.

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1 hour ago, Anders Buen said:

Slabcut backs seem to give low B1+ mode frequencies. I think the low crossgrain stiffness of the top play a significant role in violin acoustics and performance. The arching should give smaller effects from the E-modules on the main mode frequencies than for a flat plate, at least so for mode 5. The crossgrain stiffness fall fast when the ring angle is off 90 degrees. And it is quite possible to get crossgrain stiffnesses lower than the general tangential stiffness of spruce may give alone.

Of of the main reasons for not using slabcut spruce is the larger humidity creep and swell in the tangential direction. I think that may be the case for the maple backs too, although the differences probaly are smaller for maple than for spruce.   

 

1 hour ago, Anders Buen said:

Slabcut backs seem to give low B1+ mode frequencies. I think the low crossgrain stiffness of the top play a significant role in violin acoustics and performance. The arching should give smaller effects from the E-modules on the main mode frequencies than for a flat plate, at least so for mode 5. The crossgrain stiffness fall fast when the ring angle is off 90 degrees. And it is quite possible to get crossgrain stiffnesses lower than the general tangential stiffness of spruce may give alone.

Of of the main reasons for not using slabcut spruce is the larger humidity creep and swell in the tangential direction. I think that may be the case for the maple backs too, although the differences probaly are smaller for maple than for spruce.   

I completely agree with that.

Another advantage of using radial cut wood is that it is very easy to make the plate that way.  A round tree trunk log section is easily split into narrow wedges with radial directions.  Two of these are joined on their thick edges to form a plate with the center joint going along the thick edges. The resultant plate has the annual rings 90 degrees to the flat surfaces and as you pointed out this is the stiffest possible cross grain elastic modulus.

This splitting method also helps to ensure each assembled plate has similar cross grain stiffnesses and the original outline shape of the violin was optimized for split wood with this uniform high elastic modulus.

In order to get an off 90 degree angle or a more tangental cut the tree trunk has to be cut with a saw. This is a tedious task if a hand powered saw is used but modern saw mills do this quickly. A tree log slab cut with a saw generates plates with various ring angles to the surface --from perfect 90 degrees with a center cut down the center of the log, and close to 0 degrees near the outside of the log.  

Thus the cross grain elastic modulus vary greatly with sawn cut wood and plates even made from the same log section would have very inconsistent stiffnesses and mode frequencies and the assembled violins would probably also have inconsistent sound characters.

The bout widths of a violin can be adjusted to achieve the same bending stiffnesses and mode frequencies. A sawn plate made with wood having off-perpendicular rings should me made narrower.  This of course is never done because the traditional violin outline shape, which was optimized for split wood, is sacred.  

 

 

 

 

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