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| Free plate tuning - first results http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23721 |
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| Author: | Edzard [ Mon Sep 07, 2009 9:56 am ] |
| Post subject: | Free plate tuning - first results |
Hello All, After watching Alan's DVD (several times..) on free plate tuning I thought I give it a try on my newest build, a J200. The top was already “hand tuned”, so the pestering with some glitter and a frequency generator was more as a reference. The top is a Sikta Spruce with standard X-bracing. The bracing is tapered. Some of the things I noticed was that is pretty difficult (=experience) to tune-in the right frequency. 1 or 2 Hertz off, and your beyond a certain mode. Also the placement of the pads under the top is something that influences the movement a lot. As the modes changes, you have to change the pads also. In the excitement (and noise) you forget this. Ear-protection is a must. I didn’t have one and had to stop after 30 minutes. I couldn’t bear it anymore.. Anyway, I included some pictures of the different modes I encountered during the search. Picture A: 68,89 Hz Picture B: 104,31 Hz Picture C: 154,25 Hz Picture D: 252,13 Hz I suppose that the last picture is the ring-and-a-half mode? Would it be useful to close it up (the ring) with regards to the already reached frequency? Kind regards, Edzard |
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| Author: | Burton LeGeyt [ Mon Sep 07, 2009 11:06 am ] |
| Post subject: | Re: Free plate tuning - first results |
It does appear that your last photo is the ring and a half. I think it would be useful to close it more than it is. 252 Hz is a fine number but you can lower it a little as you try to close the circle and still be okay. My last large guitar came in at 247 and was not closed but sounded fine. I like to trim the plate to as close to its final size as possible also, it can alter the shapes and frequencies slightly and it gives you a more accurate idea of the weight. Little things like slight discrepencies in side to side width can throw off your clean node lines. If you do work more at it I would be very interested to see what you changed on the bracing to alter the mode shapes. |
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| Author: | Alan Carruth [ Mon Sep 07, 2009 12:15 pm ] |
| Post subject: | Re: Free plate tuning - first results |
Try taking a little bit of wood (a LITTLE BIT) off the ends of the X braces for, say, 3" or so in from the sides. The lower end of the bottom tone bar might also work. These can get quite low without compromising the structural integrity of the top. That should help close up the lower part of the ring. I find that on 'standard' braced tops it's often hard to close up the side of the ring, or, if you do, it might end up as a 'fish tail'; sort of one half of a parenthesis stuck on the side of the ring, facing out. You could probably go as low as 135 Hz for the ring+, but that's something of a judgement call. |
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| Author: | Burton LeGeyt [ Mon Sep 07, 2009 3:01 pm ] |
| Post subject: | Re: Free plate tuning - first results |
I'm pretty sure Al meant 235Hz. FWIW I have had some come in down near 210 but that seems to be against everyone's better judgment. They are fine so far but it makes me nervous. |
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| Author: | Edzard [ Mon Sep 07, 2009 3:08 pm ] |
| Post subject: | Re: Free plate tuning - first results |
Thanks Burton and Alan for your responses. I will try out this tomorrow and post the result/difference. Is there any reason to chase after other modes than the "ring-and-a-half"? Regards, Edzard |
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| Author: | Darryl Young [ Mon Sep 07, 2009 7:23 pm ] |
| Post subject: | Re: Free plate tuning - first results |
Burton and Al, When elluding to how low you can take the frequency on the ring-and-a-half mode, does the size of the guitar matter? For instance, wouldn't you want the frequency a little lower on an OM sized guitar than you would a dreadnaught to affect the tone similarly? If the answer is yes, to what size guitar do the frequencies you mention apply? |
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| Author: | Edzard [ Tue Sep 08, 2009 2:07 pm ] |
| Post subject: | Re: Free plate tuning - first results |
Well I shaved of some wood on the X brachings. Didn't touch the bottom tone bars as they already pretty thin (on the end). The frequency dropped to 248,25. I started using coloured sand, to me it seems that it better responds then the glitter. As for the picture: the lines are clearer, but also the opening on the right side.. Maybe a little bit more of shaving the X brachings will close it. Edzard |
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| Author: | Alan Carruth [ Wed Sep 09, 2009 12:29 pm ] |
| Post subject: | Re: Free plate tuning - first results |
I often trace the ring+ node lines on the top so that I can see what small changes there may have been from an alteration like shaving the braces. It looks to me as though the ring may have closed up a bit on the upper right side, and the opening on the left is also differetn from what it was in the first photo. I think you're on the right track. Also, Burton was right: that should be 235 Hz. It's amazing what you can miss in proofreading! |
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| Author: | truckjohn [ Wed Sep 09, 2009 12:58 pm ] |
| Post subject: | Re: Free plate tuning - first results |
On a smaller top.... It will naturally have a higher frequency for the same thickness and physical properties than a respectively larger top... It is smaller and as such, naturally stiffer. So if you got it back down to the same frequency as a larger top... it would be that much thinner. Now... whether to shoot for a higher, same, or lower frequency on a smaller top... I have my own theory... but it isn't based on any actual experience.... I have to leave that question to someone who actually knows the answer... Good luck John |
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| Author: | Burton LeGeyt [ Wed Sep 09, 2009 1:06 pm ] |
| Post subject: | Re: Free plate tuning - first results |
Often times when I get those patterns that you are seeing for the ring+ I get 2 modes that occur within 5-10 Hz of each other and are mirrors of each other. One is open on one side and the other on the other side. I was told that it can be caused sometimes by uneven lower x brace legs and careful attention there has "joined" them into one smooth circle shape. This happens a lot for me. Other modes to look for are the one directly below the ring+ which usually looks like a horseshoe up around the soundhole with a little frown in the lower bout. I don't try to manipulate it but I do pay attention to how close it is to the ring+. I like to see what the really high ones are doing also, in the 450-650 range. Sometimes I find a lot, sometimes not. And sometimes they are clean and symmetrical and other times just wierd. Darryl, as to your question I don't know. My gut says that you would look for the same number no matter the body size but this is one of those times I am not confident of my answer. My numbers jump around a bit. The lower numbers tend to have a more fingerstyle responsive feel but again I don't have enough data to make any conclusions. As for the 210 and 245 numbers, I have had large and small guitars come in at both of these. Sorry that isn't much help. Bear in mind too that I am mostly a beginner at this. I answer these questions, but my experience is limited to a little over a year of work with this method. A lot of what I am doing is working from clues mostly from Al and Mark, almost all of which is in the archives here. Edzard, the red sand looks cool. If your tone bars are touching your x brace you might try to shave where they meet down to a very little bit. Sometimes that helps with some of the symmetry problems of the ring+ with a non-symmetrical bracing pattern. |
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| Author: | John Platko [ Thu Sep 10, 2009 1:54 pm ] |
| Post subject: | Re: Free plate tuning - first results |
If you post more pictures, Edzart, a picture of the braces would be helpful to me. John |
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| Author: | Alan Carruth [ Thu Sep 10, 2009 7:59 pm ] |
| Post subject: | Re: Free plate tuning - first results |
I tend to see the 'ring+' at the same frequency, more or less, on all sizes of guitar. On the bigger ones that will mean a relatively ticker soundboard and stiffer bracing, but that's what you need on the longer span to withstand the static torque. I'm not saying that's absolutely the 'scientific' answer, and what it 'should' be, it's just more or less what I see. |
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