Jump to content


Johnmasters

Member Since 15 Aug 2005
Offline Last Active May 23 2016 10:21 AM

Topics I've Started

My Wien Bridge Comparitor

10 March 2016 - 04:39 PM

.


CONFORMAL mappings

09 October 2015 - 11:57 AM

These are interesting.  I think that "Raguz" or Mr. Robert Zuger actually is intending to do something like this.  If he used the word "conformal map"  he could write the whole thing in 100 words or less.

 

I think he makes a transverse line at the post and either side is intended to be what we would call a conformal map of the opposite side.  (flipped over as in a mirror)   Doing this would map points of one end of the violin into the other end.  At corresponding points,  the thicknesses and arch height would be the same.  But did he really arrive at a true conformal map ??   I don't know,  I am asking HIM.

 

I arrived at this in a period of waking up from my sleep.  I often get insights this way.  I recalled that on his website, Mr. Zuger drew a rectangle and drew in it a violin with top and bottom the same size and shape.   Then he moved (continuously) the rectangle sides outward to make a trapezoid.  The drawing went along for the ride.  I thought it was a complete fudge and I threw out the idea completely.  Jim Woodhouse had asked me to take a look at Zuger and I wondered why Jim was not alarmed at this strange pseudo-science.  I now see something of interest.  If only Mr. Zuger had the word "conformal map" in his model,  he could have boiled down his website to a single page.

 

If y'all find this interesting,  I can post more about the special properties of conformal maps.  In the meantime,  here is a page with many illustrations of conformal maps.   Notice that they preserve angles and shapes at CORRESPONDING POINTS but not "all over the map'  as one could say.  That is to say,  they preserve shapes and angles LOCALLY.  A transformation exists,  but it varies as one moves through one of the areas.  (If you choose the other area,  you use the inverse of the transformation.)

 

http://images.search...fullyhosted_003


For the math geeks

24 September 2015 - 12:23 PM

I corresponded with ABAQUS student addition manager about a problem with installation and he took an interest in my usage. Here is a site if anyone wants to see how FEA is being used by someone involved with guitars.

He is just revising his site, so perhaps it will eventually be interesting.

https://sites.google...alguitardesign/

Smashed cello top

10 September 2015 - 05:47 PM

I am finishing a smashed cello top for a school. It was a more than a bssic cello, but I offered to fix it cheap as an experiment.

Cleats went under a new bassbar and a shoe inserted for the soundpost which had passed through the top. This was a tiny bassbar-like thingy about 2.5" long with a conical hole in the center. I will make a post with a point to fit in that.

I have done this before for that school, and such a soundpost-hole repair delighted the teacher. The cello was actually better in sound, perhaps because the old post was not fitting.

But that is not what I wanted to say ......... This newer repair had me revarnishing the entire top. So far so good. But now that I am gluing it on, I see that the top has extra perimeter all around.

That must because the arching has flattened out. I won't try to work this out, but it seems to me that a couple of props would push up the arching and allow regluing in the old position, the outline being shown by the remaining varnish on the underside of the top (next to the ribs)

I again wonder if the ventral pin could not have been what is left after such a prop is cut away. Pushing a top to fit tapered ribs in the upper part causes a very noticeable flattening of an arch. It is easily visible to the eye.

I think that if I had put such a prop up between the upper corners (glued into a conical hole) and one between the lower corners (this time not glued in, just put in with soundpost setter.) the arch could remain proud.

I have mentioned this before. Now, I see that the idea of the conical hole being made by the end of an auger bit is also appealing. But what about this other business of a prop ?

Longitudinal Arching

03 September 2015 - 03:02 PM

Uncle Duke has asked me to suggest a good longitudinal arching.

I was able to fit my function to a photograph posted by Mr. Hargrave (I think it was)

Anyway, the shape from the middle of the top to each end was given as cosine to a power of something in the range of 1.3 to 1.7

Of course, calculating all these and plotting by hand is tedious. Just to see the shapes, anyone can go to

http://www.mathgv.com/

and download this software for free. I can then send files for experimental graphs I have made.

They look very close to what I like in an long arch that looks like the old-timers.