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| CHladni troubles. Is this a ring+? http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50822 |
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| Author: | Dave Livermore [ Wed Jul 18, 2018 3:29 pm ] |
| Post subject: | CHladni troubles. Is this a ring+? |
I am working on an experiment. Can not find the ring plus If you are familiar with this, please check out the photos and let me know which one you think it migt be. Based on the others I have tuned, it should be about 250hz. But there is nothing there. Any help will be appreciated. (I would give full details but i have crashed three times attaching photos and am real frustrated right now.) Thanks, Dave |
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| Author: | Dave Livermore [ Thu Jul 19, 2018 4:56 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
Someone? Anyone? Bueler... Bueler... |
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| Author: | meddlingfool [ Thu Jul 19, 2018 5:03 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
None of them look like it to me. It's meant to represent the main monopole, yeah? I only know what it looks like on a closed box, sorry. |
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| Author: | meddlingfool [ Thu Jul 19, 2018 5:05 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
If you have some sort of FFT measuring device, you should be able to support it at the corners, tap the bridge area, and find what the freq is, then try running the waves at that freq to see what happens. |
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| Author: | peter.coombe [ Thu Jul 19, 2018 6:40 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
Asymmetric tops are difficult, and Adirondack tops are the most difficult to get the closed ring. Looks like you have both. If I had to guess I would guess the last picture. What are the frequencies? |
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| Author: | Dave Livermore [ Thu Jul 19, 2018 7:16 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
The last picture is 229hz. Glad to know I am not com pletely inept. The pics all have a gauge in them so you can see the hz. It is sitka. Asymmetrical. 229 is right where I would think it should be, but it looks nothing like it should. So how would you approach it? Leave as is? Typically when I find something like this I shave the x until it is next to nill then start over. I don’t want to start over. I want to make a guitar. Something different. But a guitar that sounds good would be a huge bonus. The plan for this is a fan fret. 25.5x24.625” 12 fret join at body, cutaway so 14 fret access if needed,( but seriously, who plays up there on an acoustic?!!) Arm bevel Two great big sound ports (cuz 2 is better than 1 right?) No sound hole Possibly open peg head It is what I call an everything guitar. |
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| Author: | truckjohn [ Thu Jul 19, 2018 8:07 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
Many of those modes seem to run diagonal across the top.... Makes me wonder if you have a very strong diagonal mode that is masking the ring +. Any chance the top has significant runout. I would ping Al Carruth and Trevor Gore. |
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| Author: | Alan Carruth [ Thu Jul 19, 2018 8:17 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
I wish your little frequency gauge was easier to read! I've never made a top without an upper transverse brace, so I suspect that's what's causing the problem. The upper node line, the 'half ring', usually runs more or less along that brace. You may not have enough cross stiffness in the upper bout to get it to do that. The hardest thing about learning to work with Chladni patterns in learning how to find them. One thing I did to practice 'way back when I was starting to play with modes was to hack up some plates of expanded styrene bead board to see what they did. It's a good learning tool because the stuff is cheap, easy to get, light weight, easy to shape, and has high damping and the same stiffness in all directions. This is not true of a lot of other stuff, such as Masonite, or extruded foam board. The way to tell if the stiffness is the same is to cut a perfect square of the stuff and see what you get. If the stiffness is uniform along and across the piece the second mode will be an 'X' that goes right from corner to corner with straight node lines, and the third one a closed 'ring'. The 'ring' mode frequency will be just a bit higher than the 'X'. The light weight and high damping spread the modes out in frequency, so that they're easy to find (just wait until you try glass....!). Anyway, if you make that bead board square the first six modes will correspond quite well with most of the lower modes on a guitar top. The 'ring' on the square plate actually doesn't look like a ring on a flat top guitar top because the UTB stiffens the upper bout too much in the cross direction, while the lower bout is too wide and/or not stiff enough to get the ring to 'close' there. The square plate mode that is probably the closest to the 'ring+'on a normal guitar top is a higher one, comprised of a ring in the middle of the plate with short curved diagonals across each corner. (I tried to do some ASCII art but am not having much luck: it would probably not come through right anyway) In any event, on a guitar top the UTB stiffens the upper bout so much across the grain that the two corner diagonals flatten out to become the upper half ring. You actually do see the lower daigonals sometimes, particularly on Classical guitars, as curved lines outside of the ring, thusly: )0( So, why no UTB? I'd worry that even with the 'A' brace you'd get a lot of neck rise without one. |
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| Author: | Dave Livermore [ Thu Jul 19, 2018 9:41 pm ] |
| Post subject: | Re: CHladni troubles. Is this a ring+? |
Thanks for the responses! The lack of transverse brace is a whim, like the rest of this build. But I know these things follow the laws of physics and that I should be able to get just about any guitar top to do what I want it to do. And this has presented itself as a fantastic challenge. my brain tells me that if I get the ring+ to close, I will have a guitar that is consistent with others that have closed. But maybe that sound it isn’t the holy grail. Al is right. I should experiment. In the mean time, I will do a little more tinkering and then close this box up and see what I got. |
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