hi,
what can you read and conclude from this pic of my chladni?
cheers
Fric
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| Author: | fric [ Thu Nov 12, 2009 2:55 am ] |
| Post subject: | chladni pic |
hi, what can you read and conclude from this pic of my chladni? cheers Fric |
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| Author: | Bob Garrish [ Thu Nov 12, 2009 11:37 am ] |
| Post subject: | Re: chladni pic |
Generally the useful information comes from the modes of the plate before it's attached to the guitar. For example: The mode at 245 is a closed ring (and has to be, since the top is glued to a big stiff rim) but there's no saying how clean that mode would have been when the plate was 'free'. A constrained top is forced into a ring mode so, as the thinking goes, the closer it looks to that -before- it's glued on, the more free it will be to vibrate when forced into that mode. |
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| Author: | Darryl Young [ Thu Nov 12, 2009 12:59 pm ] |
| Post subject: | Re: chladni pic |
Fric, I'm not experienced enough to comment from lessons I've learned. I will repeat what I've read and you take it with a grain of salt. Once the top is glued to the rim, the rim forces the top to form particular Chaldni patterns. So a low quality, cheap guitar looks similar to a high end, awesome sounding guitar. At least I'm not aware anyone can discern tonal differences based on pattern shapes of a top glued to the rim. |
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| Author: | Alan Carruth [ Thu Nov 12, 2009 7:24 pm ] |
| Post subject: | Re: chladni pic |
You seem to have essentially the same 'cross dipole' pattern at three different frequencies. The only ways this can happen are that your signal generator is putting out some harmonics, you're driving the top too hard, or there's something else near the top's cross dipole pitch that's coupling with it. I suspect one of the first two, because the three modes show up at very nearly harmonic frequencies: 90, 177, and 354. Check the back, though. The 'ring' or 'main top' mode is usually at around 200 Hz, more or less. It's actually one half of the 'bass reflex couple' with the air in the box, and the air mode is generally an octave down. If the smudge of glitter just below the center of the bridge is jumping at 90 Hz, that coule be the 'main air' mode, with the whole lower bout moving in and out like a loudspeaker, pushed by air pressure changes in the box. See if you can find the other half. Try driving the top just below the bridge on the center line, around 350-450 Hz, and see if you can't turn up the 'long dipole' mode. It might well show up twice, sice it couples with one of the inside air modes. The higher order modes are intersting. They certainly effect the sound of the guitar, but I'm not sure how. |
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| Author: | Parser [ Thu Nov 12, 2009 7:51 pm ] |
| Post subject: | Re: chladni pic |
I can't figure out why...but I LOVE those patterns! 
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| Author: | fric [ Fri Nov 13, 2009 3:12 am ] |
| Post subject: | Re: chladni pic |
Thank's all for reply. Alan , I will check my electronics (does it give clean sinus signal) ,but you are right I drive top hard (about 17W) so for the weekend I will make new tests and new aproach.(sinus will kill me)! Another question is according to phot 5-440 will I have wolf note on high E-5 fret regards |
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| Author: | Alan Carruth [ Fri Nov 13, 2009 1:44 pm ] |
| Post subject: | Re: chladni pic |
fric asked: "Another question is according to phot 5-440 will I have wolf note on high E-5 fret" Probably not, so long as your bridge is not too light. |
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