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setarmaker
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Oud Structure's Question
I just needed to know if the end of all braces are attached and glued to the top ribs of an oud. If Yes. Could someone please explain about, how the
soundboard resonates then? How does it stay resonating while, playing it? This is what I noticed in an old oud (made by Ali Al-Ajami in1950's) which,
came a cross recently and I looked inside of it by using a dentists mirror. Thanks a ton for replying to me.
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jdowning
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It is important for the ends of the bars to be glued to the top ribs of a lute so the same should apply to an oud. The bars provide structural support
for the soundboard against collapsing under downward pressure due to string tension loads etc. If the end of the bars become unglued the sound board
may start to sink at the edges.
The question of how a braced soundboard vibrates is very complex and I doubt if anyone fully understands or can measure what is going on. Luthiers
usually determine the optimum solution that works for them through long experience gained in making many instruments.
The bars are relatively deep in section (for vertical structural rigidity) but are reduced in depth at each end and are relatively narrow in width so
can flex in torsion as well as a bit in bending. The soundboard is usually quite thin (less than 2mm) and can flex and vibrate relatively freely
between the bars. Also the edges of the soundboard glued to the thin top ribs are often weakened by purfling or banding a situation that will in turn
affect soundboard response.
The whole structure of a good responsive instrument is supposed to be light in weight and just sufficiently strong to withstand the string tension
without collapsing. On the other hand I recall seeing a film many years ago of an Arabic luthier standing on the inverted bowl of one of his completed
instruments in order to demonstrate how strong it was. Interesting (not to mention nerve wracking to watch) but not to be recommended!
Regardless of any theoretical explanations the system does work.
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Dr. Oud
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While the braces in some ouds are tall and thin, there are other designs that work quite well. Gamil George, for instance made the soundboard a bit
thicker and the braces a little wider and much shorter. This configuration is used my Shahata today, who's father was ana pprentice in Gamil George's
shop. Manol offset the center of the braces toward the treble side and cut down the brace under the smalll roses. His design is used by nearly every
Turkish builder. The position of the sound holes and braces can affect the response of the soundboard, but it seems many configurations will work as
the variation is nearly infinite. I did a survey of the placement of the tone brace - the one just forward of the bridge that determines the primary
resonant frequency node point. Measurements aere taken on 10 Nahats and the placement varied by as much as 6.5% and this was within the same family of
makers.
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setarmaker
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Thanks for your quick respond guys. Gluing bracings to the ribs was a storm braining to me. I make different instruments but, Just being a
professional Structural engineer for 17 years, when I looked at the back of an old oud’s soundboard, I realized that the design of the soundboard
and the bracings are just the way we design structural floor for earthquake purposes e.g. we try to keep the centroid of the floor shape coincide with
the center of the gravity of the floor. Scientifically, and practically, this will result in the best vibration mode of the floor in case of
earthquake with the least damage. The vibration will mach the received frequencies caused by the earthquake. Thus, from my engineering stand point,
size of the sound holes, shape of the soundboard, thickness and height of the bracings are very much important in order to get these two points on top
of each other, I believe regardless of luthiers’ skills or wood quality.
Now, it will be a very simple procedure to do this. When you have completed the soundboard sanded down to your desired thickness and sound holes are
in place plus all other top works are done, simply put the soundboard on the tip of your index finger to see the equilibrium by trial and error. Then
mark this point and measure the distance from any reference point you’d like ( I recommend the center of big sound hole). Since your soundboard is
made of a same wood in its entire body, and since the thickness is varied by 0.1 to .4 mm you can logically and practically assume that, the point
which you just marked is the both centroid and center of mass (gravity) for the soundboard only.
By adding each bracing on the back, you are moving the center of mass away from center of the soundboards geometry (centroid). This will be solved
simply. From this I can tell you why in NAHAT Ouds, you see the bracings heights are a bit different. In my opinion, they have been trying to keep
these two centers coincide and this is what the mass of bracings will rule out only.
This is just a thought My friends, just for you and others who may be interested. If you are interested on the topic, I can show you how to find the
correct height and location of each bracing to ensure highest vibration and stability of the soundboard regardless of any shape of bracing. ( just
needs to be from same family and shape in a certain oud but you can change it for a different shape and get same result).
If you use 8 bracings, 9 or 6 it really doesn’t matter. The last bracing’s location and thickness and height will guarantee the balance. On an old
oud that I happen to see, I took all steps above and from the Static formulas, I simply determined the location and height of the last bracing and it
was accurate to the original design by zero tolerance. When I say last bracing, it just means the last on you would like to apply. In this case my
last bracing was considered as the one under two smaller sound holes.
Thanks a gain, Ahmad
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Dr. Oud
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ok, then how do you explain the asymmetric design of the Manol soundboard? The sound of these ouds is testimony to the efficacy of the design, but the
size and shape don't follow your hypothesis. For one thing, wood is not an isotropic material, which changes the science of oud making into an art.
hmmmm?
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jdowning
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I am not a structural engineer but would be very surprised if buildings were designed to sustain earthquake loadings based only on a simple, two
dimensional, static analysis. Dynamic analysis must surely play a significant, more difficult to determine and likely more crucial part in the design
process? And so it must be with an oud, lute or other musical instrument.
Of course, the basic objective of a luthier should be to achieve an overall uniformity and balance in the soundboard geometry and barring as a
starting point, as dictated by tradition, but the fine tuning of that basic arrangement - which can make the difference between a superb sounding
instrument and one that is barely mediocre, as Richard observes, is surely much more subtle than just arranging for the centroid (the centre of area
of the soundboard) to be coincident with the centre of gravity of the soundboard?
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setarmaker
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Good and strong comments on my later posting.
1. I'm not an oud maker, so I probably need to except what you say as an expert. This is fine. but I'm so glad hearing about dynamic behavior of the
soundboard. I feel more comfortable talking to someone who's got some knowledge about what I just discussed. What I mentioned was not about how an
ouds sound could be enhanced, but just a thought. Asymmetric design of bracing is just perfectly matching what I explained in my previous post. I
emphasized that, It does not matter where you put all of your bracings except for the last bracing. That means it could be accidentally symmetrical or
asymmetrical dipending on your mass distributions. this is my point.
2. Have you guys ever tried the steps that I have mentioned before in any of your projects? If not, please go ahead and send me an example of one of
your ouds. What I need is the average of your soundboard thickness, the number of bracing minus one and all specifications of all of your desired
bracings. I may be able to tell you where you need to install your last bracing in both practical and theoretical ways.
3. For the ones who are concerned about Dynamic behavior of the soundboard, I was expecting a different argument! Why no one asks me the question of "
how the heck a Luthier would now all about modern structural theories in for example 1800s"? This would explain why I just started with static
equilibrium at the beginning. Old master luthiers might not now any thing about all these things but might have learned everything from their
masters in practical ways.
4. The good thing about what I explained before is that you can make the procedure in both mathematical and practical ways. I'd love to explain both
ways which will result in a same conclusion. but the dynamic exploration which is a more accurate way is possible only through some mathematical
approaches such as matrix and dynamic structures theories knowledge. I'd love to explain dynamic behavior as well, but it may not be a useful
presentation for every luthiers.
5. I strongly believe that, an instrument will sound perfect if a good and right old wood, a skilled luthier with an accurate ear, lots of years of
experience and a touch of spirit meet at a right time simultaneously. But as I mentioned before, this is just a thought of mine.
you guys give it a try and check it out. It's worth it to try it, if my concept is new to you. If there are 100 points needed to make an instrument
perfect, my understanding of bracing arrangement could just be one out of 100.
6. I'm trying to get some sleep now, but I will explain how all this would work in a traditional way with no need of math, physics or structural
engineering knowledge.
7. isotropic material issue. I 100% agree that wood is not an isotropic material as you mentioned. Since no instrument is100% perfect ( not talking
about exceptional deals), a 2mm thick wood material can be considered somewhat as an isotropic material. for such dedicated member, calculations show
an ignorable discrepancy in determining center of mass and centroid. Please check this and let me know if I'm wrong.
8. I'm not new in playing and making lute instruments, but I would never want to put my nose in oud business. All I had was an honest curiosity.
9. Dreams will come true some day if you honestly believe them.
Thanks, Ahmad
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Peyman
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Very interesting discussion. Ahmad, I sent you a u2u (up in the page).
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jdowning
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Don't get me wrong Ahmad I am very interested in your thoughts and the discussion thread on this subject as one never can tell where they might lead
in a positive way to the benefit of all.
If you have not put your theory into practice as an instrument maker then I think that you should first make a series of test instruments and then
publish the results rather than requesting others to do that work for you. This is your project after all.
Sound enhancement of an instrument (however that may be judged from person to person) is what it is all about as we would all like to know how we can
get rid of some of the 'mystery' and consistently build good instruments in a more 'scientific' manner. Of course luthiers - past or present - do not
know about modern structural theory - they don't need to in order to make fine sounding instruments based on their experience. In any case, I very
much doubt if a mathematical model of oud soundboards can be developed to reliably predict dynamic behaviour so that the data might be simply
expressed in a form that can be of use to an instrument maker - but I remain open minded about that. Your expertise as an engineer will be needed to
translate the complex mathematical language of matrices etc. into plain written language that we can all understand so I look forward to that.
Like you, I have approached the oud from my experiences with the lute and other stringed instruments of the 16th and 17th C Western societies. As
there may be more historical information surviving about the construction of the lute than there is about the oud as the two instruments are
historically connected and - structurally - are essentially the same, I figure that oud makers might find something of interest and relevance among
this information.
Here, for example is part of a text relating to lute barring taken from Harmonie Universelle by Marin Mersenne, Paris 1636 a massive and important
theoretical work of the time. It is taken from Book 2, Proposition 2, pages 49-50. It is in 17th C French with phonetic spelling so I will follow this
posting with my translation into English.
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jdowning
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.... and here is my translation of the relevant bits of the text for information. I am not fluent in French so my translation may not be perfect but
should, I trust, reasonably convey what Mersenne was saying.
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SamirCanada
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Did you ever concider this... beuty is the ears of the beholder.
Wich makes me say that the basis on wich we determine a good sounding oud cant just be scientific.
Because If you can produce the loudest possible oud doesnt mean its the best sounding oud.
Personaly I cant stand if the trebles on my oud are ringy and really loud. I like a more closed sound to them so that they sound rounder and softer.
You can get pretty close to that result with mathematical calculations Iam sure (if your aiming for that). But not if your aiming to maximize every
aspect of the sound. So in the objective of trying to build the perfect oud that responds to all kinds of frequencies we might be going against the
true sound an oud should have. Thats why you will hear many people complain that there oud has too many overtones. And thats why that before one gets
into trying to maximize the sound of a oud they should know how a good oud sounds. If its made to sound like a lute or a guitar then its not a oud
anymore, It looses its soul I find. The master makers before us left us there beutifull ouds and it is an evolution of many many years to get here.
And they are a few aprentices left to carry on the art.
And on a side note many oud makers will make 2 identical ouds and they will sound differently it must depend on a ton of reasons that cannot be
controled by the human hand. my guess
This is based solely on my opinions and some of my fellow oud players.
What do you think about this?
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Dr. Oud
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I don't know about the number and/or positions of bars/braces in French lutes as the translation mentions only 6, while the ouds I've observed (more
than a few) have 7 or eight. re: mass centroid analysis - It would take only a few experiments with different pieces of wood to discover that the
stiffness of each pice varies even between pieces of exactly the same dimensions and at the thin dimensions of an oud, varies quite dramatially. It
is the stiffness that determines the physical response to the string vibrations, not the mass. Stiffness is not necessarily related to the mass, but
rather depends on grain density, ring count, runout and varies even within each specific species of wood. I have discussed the dynamic analysis of
soundboards with simulation engineers at my company and they feel that as the components are stressed at the boundary of their limits, the analysis
cannot be conclusive. The complexity of the structure also defies computer simulation, much less a simple mathmatecal analysis. I still believe it's
art, not science.
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jdowning
Oud Junkie
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I agree with you Samir. Certainly I would doubt if an oud that only had two bars - for example - situated, say, above and below the main soundhole,
would have much of the anticipated sound characteristics that defines an oud. These structural features for oud, lute, guitar or what have you have
all been basically figured out through long tradition but it is still up to the individual luthiers, through experience, to get the best response and
finest sound from the instrument that they are building given the particular characteristics of the materials they have on hand.
Ahmad, to return again to the question that you opened your topic with - i.e. are the ends of the bars glued to the ribs - here is another reference
that may be of interest - taken from Musick's Monument by Thomas Mace, London 1676 in which he is giving instruction on how to repair and maintain
your own lute. He confirms the importance of the bar ends being firmly glued to the ribs.
"Because the belly being so very thin, and only supported with six or seven small weak bars, and by the constant stretch of the strings, (which is a
great strength) the belly will commonly sink upon the first bar next above the bridge, but sometimes upon any other, and so cause it to let go its
hold at the ends of the bar, and then your lute will jarr and grow unpleasant.
And if it not timely amended, worse inconveniences will follow, which may endanger the spoiling of the belly. Therefore, whenever a bar is loose, let
it be quickly amended or presently set your lute down to a lower pitch, or untwist your strings, and lay it by, till you can get it mended."
Sound advice especially in the wet English climate of Mace's time when "Misty Vapours and Dampness" played havoc with the lute and its tuning.
I may post the full text of Mace's instructions later as a separate thread as they are just as relevant to the oud as they are to the lute.
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jdowning
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Doc - the number of bars in Mersenne's description is only the basic minimum number.There might be more (and there usually are in a lute) - as
Mersenne states - dependant upon the experience of the individual luthier and the type of lute being built, number of strings etc.
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setarmaker
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wow! Thanks guys. I deeply appreciate mike for putting this beautiful forum site together. It is a wonderful tool so we all can chat and educate each
other. I truly loved the translation of lute construction. thanks a ton. I thinks my English is not good enough to have a better explanation for my
thoughts. I believe most part of your discussion. As I said before, I don't play Electric guitar! I play Iranian Tar and Setar. By ear not by note. I
trust my ear and tune piano by my ear so confidently. So, I'm deeply involved with spiritual part of the deal. you are all right. It's not all about
math. Or we may even say that, it has nothing to do with math.
fair enough. As I said, we do not need to know any math to follow up on my primitive theory. One can simply do it by a trial and error. I have seen so
many amazing lute instruments in my life which proof what you all say. lot's of them did not even meet the minimum qualifications of a wonderful
instrument but, they sounded brilliant! I've seen soundboard which, you won't believe their sound quality with an ugly grain pattern. Todays luthiers
may use such wood for their fire place only. It seems like the old masters new how to talk to those woods and new how to ask them to become a part of
their life by sounding well. I know all of these and I appreciate your reminder. What I posted, came to my brain as a matter of second as soon as I
saw an oud's soundboard for the first time. I may change my mind on the second or third time! who Knows?
My friend suggested that, I better to do my project by myself and try to experience it first. Certainly may friend. I did not mean to have others
working on any project of mine.
Please don't get me wrong. Come on guys, I didn't ever mean that, by using this method, your oud will sound better, lauder, warmer or more brilliant
at all. you can always use a microphone and an amplifier to make a 10,000 Watt of sound. That's not my point and far away from my subject.
My point is that, lets see thing from all directions. for instance, If I go to a physician for a particular disease, the Dr. would not necessarily
need to have self experience on that type of disease to help me out. In todays world, People work for each other without knowing each other. so there
might be some luthiers out there, who may want to go a head and give it a shot.
I'm going to take your advise and start exercising on the matter. I will definitely post some pictures and the out come of it in a near future. The
only problem is that my workshop is not prepared for oud work and most of my tools are designed for making tar and setar. But that's not a big deal. I
think that Khalaf's site may help me with some needs. Thanks again for all of the info available on this site. So my project will start with turning
down a damaged oud. I'll try to document everything by taking photos so, interested luthiers may help me with different steps.
at the end I was wondering if it would be o.k. for me to print a copy of the translation for my records. It was extremely interesting. Please let me
know if I would have the permission.
Thank you all, Ahmad
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jdowning
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Keep up the good work Ahmad. I for one look forward to your future discoveries that I hope you will post on this forum to the benefit of everyone.
Here is some good news. Interested in your theory, I tested the belly of an old oud that I am currently restoring and find that the centroid (the
'centre of gravity' of the area of the belly) coincides quite closely with the centre of gravity of the belly itself - the balance point in this case
being just below the bar under the the large rose. I did this fairly quickly and roughly - dividing a scale drawing of the area of the belly into
squares and estimating the area that way - deducting the areas of the roses etc. and of course the balance point is affected by the non vibrating part
of the belly glued over the neck block which should be deducted so this is not very precise. This oud has symmetrical barring so I am not too
surprised at this result but at least it is one possible data point for you to work with. I also have a couple of (reproduction) lute bellies that I
will also check out in the same manner to see what I can find. It is unlikely that there are very many oud bellies lying around - detached from their
bodies - but if there are, others may want to carry out the same test or at least check the position of the balance point and send you an image of the
belly so that you can determine the centroid.
Not sure how useful all of this will be to luthiers in the creation of fine instruments but interesting to explore further if you have the time.
John
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ALAMI
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Most interesting,
It is still an idea and needs to be tested, but as we are still at the theory stage, I will just expose the outlines:
John is right not much oud bellies lying around, and no one is going to rip off his Nahat neck to test a theory....well ...we still can do it.
I am thinking of a computer simulation system using dynamics rules. The oud can be built as a 3D model which is not very complicated, I agree that we
can assume the material isotropic due to its low thickness ratio.
If we have the exact measures of a soundboard and its braces (luckily measured during a repair) and the density of the woods used for the board and
the braces (or at least the relative density, ie the braces wood is 1.2 times more dense than the soundboard wood) the model will be reliable.
Same for the belly.
I received few days ago Dr oud book, It has all the dimensions so theoretically, we can build a 3D digital Nahat model (still need info on density-
density would change over age but I don't know if the variance is signicative).
Don't get me wrong, the simulation will only be reliable on the static state physical and geometrical side, it can determine the relation between the
center of geometry and the center of gravity but not reliable in anyway to simulate the vibrations (the sound of the oud).
The 3D model can keep its construction history so it could be adapted to different models made by different makers,
The only problem is that this experiment needs time.
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setarmaker
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Wonderful. I don't know how to thank both of you gentleman. obviously, without the help of professionals and experts, I will get to no where. When I
see there are some people who are interested in researching, I get more motivated and it really doesn't matter if we don't get a good result. Any
conclusion would be useful as far as continuing it or stopping it right there. Back to the old damaged oud that I have received, ( this is the one
that made me wonder about all these).
This oud belongs to Master Abd-al-wahab Shahidi in Denver Colorado. He is a wise old singer and oud player. still sings well and plays a good oud in
age of 86-87. I explained the situation to him and I asked him if I'm authorized to start restoring his oud with nope for the acceptance. At the
moment, I felt like, nothing would make him as happy as my offer and then he returned, off course, Ahmad. I trust you and I believe that, this
instrument won't become worse than what it is know.
Seems like I had a good luck in my first move. The rose is missing so the sound hole is wide open. The soundboard in an awful condition. Not only
crack are developed in over 10 areas but also the surface is not smooth anymore and where the cracks are, you can see sinking or swelling on either
side of cracks. I'll try my best to detach the belly with no damage to the ribs edges. I'll be posting some pictures of the progress. I have a simple
steam machine which was designed and built by myself. it's neat. It's got a simple temperature control gage and I use it for bending purposes. I can
strongly say that Not more than 10% of failing was recorded in my bending process so far. I have a little note book where I saved my bending
experience notes. It's a good tool to show steaming specifications for different type of wood as far as their species, thickness, original MC, thus,
the steaming time which should be somewhat optimum. Pictures will be posted next time. I use a smaller hose in order to get a better and more
concentrated steam out of the machine for detaching purposes and in order to keep ribs away from steam. Since it has not been used for a long time, I
don't want to spend time on it and I can just use a kettle with a modified output to get the same result. Hope this will go well.
Take care, Ahmad
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Dr. Oud
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| Quote: | Originally posted by ALAMI
....
I am thinking of a computer simulation system using dynamics rules. The oud can be built as a 3D model which is not very complicated, I agree that we
can assume the material isotropic due to its low thickness ratio....I received few days ago Dr oud book, It has all the dimensions so theoretically,
we can build a 3D digital Nahat model .... |
If you examine the front illustration and the dimensional
drawings you will realize that I have modeled oud in 3D already. If you like I can send you a iges or step file of the model. I did this once before
to generate a cam program to machine a plug to build a mold to fabricate a carbonfiber oud. The engineer doing the molding didn't solve the acoutic
problems with the CF soundboard and I haven't heard from him since. send me an address if you'd like the files.
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ALAMI
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Great news Doc, IGES is a fine format, It is a great time economy.
Just sent you an email.
I just had half an hour today to make a rough test on 3D bowl virtually attached to a vertical wire and tested gravity on it.
Then I deformed the geometry a bit making the bowl assymetrical and run gravity again.
Test attached as Quicktime movie (mp4)
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jdowning
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Interesting discussion Ahmed, ALAMI and Doc. Here is some more data that I can contribute to this project.
Today I looked again, in more detail, at the oud belly that I have and also of a scrapped belly from a copy that I made, some years ago, of a well
known late 16th C lute by Giovanni Hieber (Venice/ Padua - Italy). This lute is one of the few surviving instruments that has remained essentially
unmodified over the centuries. It has a string length of about 60 cm and has seven courses - so not too different geometrically from an 'average'
oud.
I built this instrument from measurements and drawings of the original provided by professional luthiers that I knew at that time. The attached images
show the original lute and my copy of the belly. As can be seen, the barring is asymmetrical (as is usual with lutes) - ignore the inked in 'fan
bracing' at the lower end of the belly , below the bridge, it does not exist in the original (I used this scrap belly to illustrate a talk that I gave
about lute construction some years ago). The inked in area at the top of the soundboard is the area glued to the neck block that does not form part of
the vibrating area of the belly but does affect the location of the centre of gravity (C.G.) of the belly when it is detached from the body of the
instrument. This section ,when discounted, lowers the measured centre of gravity a little towards the bridge - a correction that must be made when
comparing the location of the centroid and centre of gravity. In my calculations, I made this correction simply by taking moments (of area) about the
measured CG point - balancing the moment of the area on the neck block against the balancing moment of the total area of the belly. This gave me the
corrected shift of the C.G. towards the bridge. Here are my results in summary:-
Egyptian Oud (see my postings Restoration of Egyptian Oud - part 1 or Traditional Oud Barring). After correction of the Centre of Gravity balance
point as described above, the centroid position and C.G. coincided approximately within 0.25 cm.
Hieber Lute copy. Again the centroid and C.G. coincided approximately within 0.25 cm.
Given the fairly crude methodology that I used to determine the C.G. of the belly (balanced upon my finger) and estimation of areas (division into
squares) as well as using approximate moment of area calculations to correct for the redundant area of the soundboard over the neck block, these
results (if I have done the math. correctly) indicate a possible correlation between coincident C.G. and centroid as proposed by Ahmad. However, these
are only two data points and more will be required to confirm these findings.
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Melbourne
Oud Junkie
Posts: 354
Registered: 10-9-2006
Location: Mlebourne, Australia
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I have only briefly read bits and pieces of this most facinating thread, as I can hardly keep my eyes open anymore! But I would love to hear what
Jameel has to say about these points. Jameel you about?? 
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
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Note that in my analysis of the Egyptian oud and Hieber lute bellies I have taken the geometrical centre of each soundboard to be the 'centroid' -
that is the areas above and below a line drawn through this point across the belly are equal(and deducting the full area of the soundholes).
This, of course, may give a different point from the true centroid which is determined by integrating area moments - requiring the application of
calculus for an irregular shape like an oud belly - a calculation that I don't feel inclined to attempt manually. Perhaps the computer program
currently under consideration could handle this?
I should also mention that the balance point or centre of gravity for these two detached bellies occurs at the same point - that is close to the bar
at the bottom of the rose on the bridge side. Curious about this, I checked out two other bellies from instruments that I am currently building - a
copy of a 17th C lute (liuto attiorbato) and a reconstruction of a 16th C guitar - and found the balance point to be in the same location below the
soundhole. Note that these two bellies are unfinished so have yet to be trimmed to size which might affect the C.G. position but not by much I
imagine.
Interesting, given the wide variation in geomentry of the bellies.
The attached images show the two bellies in question - for information. The liuto attiorbato is asymmetrically barred with bars 2 and 3 above the
bridge position canted to be higher on the bass side than on the treble. Note also the below bridge 'fan bracing' alluded to by Mersenne.
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setarmaker
Oud Addict
Posts: 32
Registered: 3-12-2007
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Perfect. I cannot thank you enough for all hard work you have done so far. The interesting point that you brought up, does make sense. I did not
realize the neck block as none resonating part comparing to the rest of the soundboard. Your analysis for the moment of area based on the negligible
area of neck block part is in fact helping us to understand more about the relationship between C.G and centroid, specifically in our case. Nice job
cutting that. To me finding exact location of the centroid by mathematical ways is well possible, but we may not need to be that accurate. For you and
I, the concept is clear and just takes time to do it. What really is important is that, I doubt if luthiers and old masters have ever gone through the
complex calculations. I’m now working on the traditional ways of doing this so our friends who have no idea about complexity can follow through the
procedure. Your result of 0.25 cm is just close enough for me to continue coinciding concept. You’ve had a few experiences in a short time and I bit
we will find more and more down the road.
I’d like to emphasize that the centroid for all similar shapes are the same no matter what size they are e.g. H/3 for any size of triangle or
intersection of diagonals for all rectangles, squares, hexagonal, octagonal and so on. So we could expect that, most of the centroid would fall in to
somewhat the same vicinity you just mentioned. Because, most of the ouds have almost the same shape of the soundboard, But of course not the same
size. So if Ky (K =as coefficient & y= distance from end block up to the neck block just like K=1/3 in case of all triangles) is the location of
the centroid for this particular shape, the K could be a constant and Y would differ case by case. That’s may be why in any oud you can see the
centroid somewhere close to the big sound whole.
O.K. back to my project, Please see attached pictures and I will explain every step in the next posting. Detachment came out nice and fully safe.
It seems like someone screwed this up before. It makes you Cry. Must be around 70 years old. We’ll discover. It used to be a wonderful piece of
artwork, when It was original. I’ll try to post the sound of it played by Mr. Shahidi.
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setarmaker
Oud Addict
Posts: 32
Registered: 3-12-2007
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pictures
steaming
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