Official Luthiers Forum!

For my physics coursework/invesigation, my tutor sugested that I might consider looking at something related to guitar building. So I'm here to ask some questions about the engineering I could investigate, then have a look at the practicalities of actually doing it.

So my first question relates to the Young's Modulus of sound boards. in what is the most useful direction to measure the Modulus in? Also, what sort of values would I expect to see in "good" wood?
Similarly, what is deflection testing?

I was also thinking of looking at the stiffness of bracing which should be fine, and maybe soundboards, but that maybe to similar to the above to actually be worth investigating (or is it actually the same as deflection testing).

I could also test how the grain orientation and spacing affects the above? (even though i know what the outcome SHOULD be lol)

Where else could engineering be applied? I know i could investigate the tourque of the bridge and the moment on the neck, however I feel this may be impractical? I was also thinking along the lines of impedance and string velocity, but I dont think i have enough knowlege in that area (im not even sure if what i just said was correct, if you catch my drift)

Anyway, I would like to add, thank you for all your help you have given me in the past.

thanks

Jonny

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"Anything that happens, happens. Anything that in happening causes something else to happen, causes something else to happen. Anything that in happening happens again, happens again. Though not necessarily in that order." Douglas Adams

There is tons great research on Young's modulus in relation to guitar tops on the net you will have plenty of resurch data to work with. go get em. Oh and be sure to post your paper here too

Yes!!!!! I'd love to see deflection data from a top mock-up with lots of different bridges. Different string heights, different footprints (length and width), different break angles, different distances from the saddle to the front and back edges of the bridge, pin bridge vs pinless....all these effect torque on the top.

This is such a critical area and yet I have seen very little hard data and none that looks at all those factors.

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http://www.chassonguitars.com

+1 for measuring Youngs Modulus both along the grain and cross-grain. I would start by measuring many different examples of soundboards of a single species (like Sitka) to get an idea of the standard deviation within one species of wood, then move on to other species. I think there are several ways of deflection testing that will extract the Young's Modulus - you'll also have to keep track of the density of each piece of wood as you go - and I think that once you have the Young's modulus, you can calculate the resistance to bending of that wood for any cross-sectional shape (like for braces).

Another thing to consider is to see if you can tweeze out the relative importance of two modes of soundboard vibration - "drum mode" in which the top vibrates more or less normal to the plane of the top, and "torque mode" in which the twisting of the bridge activates the top in a more complicated fashion.

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The member formerly known as erikbojerik....

Take some time to review this site. The bibliography alone is surely the result of a significant amount of invested time. You may find a few things to pique your interest and assist you in the selection of a project.

http://www.guitarengineer.com/index_files/Page2240.htm

A reminder; guitar tonewood; i.e. guitar tops are not inexpensive pieces of wood and to get some relevant data on deflection characteristics may involve not only a significant sample size but also a significant investment..... unless some local luthier is willing to allow you to conduct measurements on his/her cache.

Best of luck in which ever path you pursue. I'm sure that many of us here are willing to help.

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Peter

Both the modulus measured with the grain, as well as the modulus measured perpendicular to the grain are important. Another factor is creep. It would be really cool to evaluate the effect of baking soundboard woods on a) density b) creep c) modulus and d) strength. A lot of builders (and factories) bake their wood...one reason behind this is that it removes excess moisture before gluing the top onto the sides. There are some claims as to tonal benefits as well...

Just some ideas for you..

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http://www.PeakeGuitars.com

I've been assuming that Young's modulus along the grain is most important. In part this reflects the fact that it is immediately involved in resisting bridge torque; I'm not sure how to factor in cross grain stiffness. Also, given that wood creeps, over time the crosswise stiffness would seem to become less important as the top takes more of a 'set'. It would be interesting to know if this is so, and, if the cross grain stiffness is important structurally (we already know it influences tone), how to factor it in to determine the 'proper' thickness for a top.

In measuring about fifty samples of top wood, of seven different species, I've noticed that the lengthwise E values pretty well track the density, and that all of the different species fall close to the same line, with less scatter than you might expect. This was borne out by one of the top wood suppliers I checked with, who tests a lot of his wood. This makes some sense, as all softwoods have a similar structure.

Iirc, Brian Burns got to test a lot of top wood that he borrowed from one of the suppliers; possibly LMII. That might be a good way to reduce the cost of such a project.

There are a lot of things you could study; just make sure yo upublish the results someplace where we mere mortals can find it (oh, for a 'New Journal of Guitar Acoustics'!).

Thank you all for your responses!!! ,
you have given me much to think about and read, and along with my own deliving into the internet, i have a few drafts for experiments that i could conduct. i will talk to my tutor over the next week and see what he thinks about them. if he says its not feasable, then c'est la vie (i have a few alternative ideas anyway), if he thinks its suitable then .

to help keep the cost down, i may well be able to get some funding from the college, which would be very helpful, although, not being sure on how much material would be needed atm (atleast 3 comparable smaples for every experiment). although, soundboards are supplied unjointed, so i could just buy 2 and use that as 4 samples etc. and a billet would make more than 3 braces.

i suppose there are many other off shoots to these experiments, like looking for correlation with physical charecteristics, so there should be plenty to sink my teeth into .

again, thank you for your help!

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"Anything that happens, happens. Anything that in happening causes something else to happen, causes something else to happen. Anything that in happening happens again, happens again. Though not necessarily in that order." Douglas Adams