Jump to content
Maestronet Forums

Davide Sora's bench


Recommended Posts

I still think you are missing what is happening with this method. Your observation that sound speed can be different for different density spruce tops is correct, but it. is not based strictly on density.

Let me see if I can explain it a different way.

The speed of sound in a solid is a function of its stiffness properties: Elastic modulus, Bulk modulus, Poisson ratio, AND its Density. For a grained solid like wood, one has to account for the variation of these properties between the summer and winter growths, the thickness of these layers, and things like moisture content.

As  general rule, the one can write the following formula:

Sound Speed squared = Stiffness Factor / Density

ALL OTHER THINGS BEING EQUAL, sound speed decreases with increasing density.

The stiffness factor varies depending on the direction through the wood that you are measuring the sound speed.

The sound speed is not affected by the natural mode frequency. It DETERMINES the natural mode frequency, along with the geometry factors we mentioned earlier.

Basically, if you compute the sound speed using the stiffness/density formula, you can predict the natural mode frequencies.  But you would need some way to measure those stiffness and density properties for wood. Not an easy task because it is a type of material called orthotropic, meaning the properties vary along multiple directions. But not impossible.

But if you measure the natural mode frequency using Don's method, then you can compute the sound speed. It is all the same thing, just coming at it from two different directions.

If you are seeing higher sound speeds with increasing density, it is because the stiffness factor is also increasing, or the mix of summer to winter growth is different, or there is a variation in water content.

Before we get too far afield, one might question the usefulness of a longitudinal sound speed in an instrument to generates sound by bending effects. It might be more useful to consider shear wave speed. Maybe modify Don's experiment somehow to measure vibration in cantilever beams. But the relationship between frequency and geometry and sound speed is more complicated.

 

Link to comment
Share on other sites

  • Replies 161
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Posted Images

10 hours ago, Peter K-G said:

The only way I can think of to confirm this hunch is by testing the method with a lot of different dens wood against lucci meter readings.

Here's the data I have on Lucchi vs longitudinal resonance method.  Plenty of scatter, but a definite correlation.

Impactvslucchi.jpg.3efd7825c553685d50f67bfcfcde41cf.jpg

To see how this the discrepancy in readings varied with density, this is % difference (+= Lucchi higher) vs. density.  The correlation is pretty lame, but maybe there's a trend for the readings to agree better when the density is higher. 

differencevsdensity.jpg.5a3694239d0dc3b73cb953df435e5a20.jpg

5 hours ago, ctanzio said:

Maybe modify Don's experiment somehow to measure vibration in cantilever beams. But the relationship between frequency and geometry and sound speed is more complicated.

I used to use beam frequency for speed of sound until I found the longitudinal resonance method.  There is probably some formula out there for wedge-shaped beam frequency, but I used cut rectangular samples.  In any case, the reading is exceptionally sensitive to thickness, and you have to add in a density factor.  Far more likely to have errors build up.

Bottom line is that I trust the longitudinal resonance far more than any other method, in that the math is simple and direct with minimal sources of uncertainty.  But I wouldn't trust ANY speed of sound measurement to give an accurate prediction of what will happen in the instrument, other than a vague idea of what universe you're in.  4500 m/s will most probably behave different from 6000 m/s wood.

Link to comment
Share on other sites

On 2/25/2023 at 12:54 AM, Davide Sora said:

@ctanzio and @Don Noon thanks for the insights, it's nice to have scientific consultants of your caliber available, this is the power of Maestronet.:)

Right!

It was not a bad thing to question the method. Lot of good information to think about and understand more :)

Sorry that your bench got a little messy

Link to comment
Share on other sites

  • 3 months later...
On 6/22/2023 at 6:46 AM, Davide Sora said:

Real-time application of casein inside the top plate:

https://www.youtube.com/watch?v=8bRRjIsXEmI&t=12s

A shorter video just showing my technique of applying the casein inside the top.

Hi Davide, 

Thank you for sharing your techniques and recipes! I wonder, do you apply casein to the inside of the top after installing the bass bar? Or only prior as shown in this video. 
i used your recipe and application technique but I did so after installing the bass bar. 

Link to comment
Share on other sites

8 hours ago, Dean Markel said:

Hi Davide, 

Thank you for sharing your techniques and recipes! I wonder, do you apply casein to the inside of the top after installing the bass bar? Or only prior as shown in this video. 
i used your recipe and application technique but I did so after installing the bass bar. 

Hi Dean.

Depends. For example, if after casein application and complete hardening, the frequency of the M5 should rise too much, I would adjust the thicknesses, and so remove the casein here and there. In this case, after gluing the bassbar, I would reapply it a second time. This is also the case if by gluing the bassbar the frequency becomes too high, so I would adjust the thicknesses and apply the casein again. If, on the other hand, I don't have to adjust the thicknesses, I apply it only to the bassbar.

If you are not curious about tap tones, and if you use a frame to hold the plate in the correct geometric shape to fit the bassbar, applying it only at the end (with the bassbar glued) is fine.

 

Link to comment
Share on other sites

  • 4 weeks later...

A recap of my fingerboard measure and how I take them:

https://www.youtube.com/watch?v=-5H4X-6Glu8&t=21s

Disclaimer:):

Some makers do it differently, preferring a fixed radius and scoop instead of the compound radius and scoops I use. The fingerboard will still work, but will inevitably be geometrically less accurate. For an explanation of radius vs scoop, I refer to this article:  https://fixitwithshading.com/tag/fingerboard/ 

Moreover, the fingerboard measurements are not fixed and can be varied. For example, the width at the nut could be varied from a minimum of 23mm to a maximum of 24.5mm. The longitudinal concavities could be decreased to practically zero (straight fingerboard), or increased with respect to those indicated in the video based on the playing style of the violinist or the type of strings used. The radius of curvature at the end of the fingerboard can be flattened up to a maximum of 42mm, to adapt it to a flatter bridge curve while maintaining an appropriate string height. The radius at the nut is better to keep it always the same (42mm), while the central radius will vary as a result of the other two radiuses: if you flatten the radius at the end of the fingerboard the central one will also flatten. If with 40.5 at the end, it becomes 38 at the mid-fingerboard (as shown in the video), with 41 at the end it will become 38.5 at the mid-fingerboard, with 41.5 at the end it will be 39 and with 42 it will be 39.5. The height of the sides can be increased up to 5.5mm or decreased up to 5.0mm, and the thickness of the free part of the fingerboard can be decreased up to 4.5mm or increased up to 5.5mm.

Link to comment
Share on other sites

  • 1 month later...
On 2/21/2023 at 5:14 AM, Davide Sora said:

Yes, usually a wedge is cut off and if it's worth it (good flames and fairly perpendicular grain) it's used to make matching ribs. I use a Japanese Ryoba or even Kataba saw, however one for making through cuts. A bandsaw could also be used if you have a proper one, you will need to make a special jig to make the slanted cut and you will take away more wood with the cut. But it's riskier, I prefer to cut by hand so as not to risk throwing everything away.:P

Onepiecebacksawandribs.thumb.jpg.fd80080049637601cfed72dbb5671b8d.jpg

Thanks for the advise!  I think I can get ribs out of this piece if I cut carefully.   

IMG_7377.jpg

IMG_7380.jpg

Link to comment
Share on other sites

2 minutes ago, MikeC said:

Thanks for the advise!  I think I can get ribs out of this piece if I cut carefully.  

Japanese saws are very efficient for this task, it could be done with a bandsaw as well, but just fine-tuning the setup needed to do it would take longer than just getting your handsaw and cutting.:)

Link to comment
Share on other sites

  • 1 month later...
  • 2 weeks later...
1 hour ago, ctanzio said:

Didn't watch the whole thing. Just went to the end. I believe there are quicker ways to mix your triple sec with your bourbon. But we Americans are an impatient lot when preparing our aperitivo. ;)

:lol:.

If you are impatient, you can also simply put Mastic and turpentine together and wait a few days for everything to dissolve, which is the traditional method for making Mastic Varnish, which is the protective one used to finish oil paintings. Cooking the resin serves to eliminate the balsamic fraction of the mastic and to harden it and make it more brittle, which in my opinion is better for a ground that stays just inside the surface of the wood.

It is also possible to cook a larger quantity of Mastic without adding the turpentine, then pour it onto a cold surface to make it solidify quickly. This will theoretically make it even more brittle. When you need to make the refractive ground, just take this cooked mastic, add the turpentine, and wait for it to dissolve. If you don't want to wait a few days, you can speed up the melting by heating it on the hotplate.

PS: If you didn't have the patience to watch the whole video (you bad!), wait to see when I upload the real-time sequence, whoever watches it all will win a certificate of merit!:lol:

Link to comment
Share on other sites

8 hours ago, MikeC said:

Hi Davide,  I watched it all.  :)

You don't charge enough!  I watched someone else's video, she used gum tragacanth and gum arabic with something added for color.  She charges 300 euro for the recipe.  :D

If you find someone who thinks that 300 euros are well spent for a recipe that can certainly be found in some book that costs much less... they will be welcome.   I hope no one will, but it will actually make your recipe seem highly valuable, a nice marketing move after all.;)

My compliments for your patience to watch the whole video. I challenge you to do the same with the next one that I will upload soon if you dare, which is a real-time sequence of the same video. I think it's interesting to see the real evolution of things during cooking, even if the patience required is next level.B)

Link to comment
Share on other sites

Every once in a while, I come across a video that shows such a simple trick that I feel like a complete idiot for not thinking of it myself. 

Using a clothespin to stop the hairs from jamming into the bottom of the bottle of brush cleaner is genius. You are going to save me a fortune in buying new brushes going forward.

 

Link to comment
Share on other sites

2 hours ago, ctanzio said:

Every once in a while, I come across a video that shows such a simple trick that I feel like a complete idiot for not thinking of it myself. 

Using a clothespin to stop the hairs from jamming into the bottom of the bottle of brush cleaner is genius. You are going to save me a fortune in buying new brushes going forward.

 

  I never thought that a clothespin would make me look like a "genius" :D

Link to comment
Share on other sites

On 10/26/2023 at 11:09 AM, Davide Sora said:

How I apply my Refractive/Mineral ground, in real time for fans of the real thing.B)

For those with less patience, a condensed video will follow, which will inevitably distort the actual application technique, making it seem much faster than it actually is.

Here is the condensed (short, but not much;)) video:

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
  • Recently Browsing   0 members

    • No registered users viewing this page.



×
×
  • Create New...