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| Specific Mobility http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=47127 |
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| Author: | Tom West [ Sat Jan 23, 2016 10:35 am ] |
| Post subject: | Specific Mobility |
I'm having a struggle getting a handle on Specific Mobility. Working from page 1-89 in the Gore book. I think the weight for deflection is in newtons. Given that and given made up numbers I have tried to work through the formula and am not sure if I'm even in the ballpark. Using 400 grams (4 newtons) and a deflection of .1mm the stiffness is 40. (units?) Plugging this into the formula for mass and assuming a f of 185 it works out to .0000296 (units?) Doing the Specific Mobility it comes out to 29. Wonder if any one can work the numbers and tell me if this is right or wrong. If anyone has any numbers from their own work they would be very much appreciated. Tom |
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| Author: | Ken Lewis [ Sat Jan 23, 2016 11:40 am ] |
| Post subject: | Re: Specific Mobility |
Yep. The numbers work Tom. On the high end of the Specific Mobility scale. Ken |
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| Author: | Tom West [ Sat Jan 23, 2016 11:54 am ] |
| Post subject: | Re: Specific Mobility |
Ken: Thanks, that what I wanted to know. Just made up data and quite obvious I would not be any where near this with true figures. Tom |
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| Author: | Ken Lewis [ Sat Jan 23, 2016 12:23 pm ] |
| Post subject: | Re: Specific Mobility |
I use a one and two lb. dumbbell in a setup similar to the one Jeff H. posted in your other thread. My dial indicator is in inches so I set up my spreadsheet to convert to metric and then do the calcs. The numbers on a recent build were something like this: Load...1lb. --.448kg which excel rounded to 4.3n Deflection... .0028 in. or 7.1x10^-5m (.071mm) f with sound hole closed....167hz The resultant specific mobility worked out to be 16.9 s/kgx10^-3 I like to measure bridge rotation as well when doing the SM measurements I'll also use a 2lb. load to verify that the results double. Ken |
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| Author: | Tom West [ Sat Jan 23, 2016 1:43 pm ] |
| Post subject: | Re: Specific Mobility |
Ken: Thanks for the numbers. Looks like your guitar is up there with the big boys.....Congrats and thanks again. Tom |
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| Author: | Ken Lewis [ Sat Jan 23, 2016 2:40 pm ] |
| Post subject: | Re: Specific Mobility |
Yeah Tom that guitar is quite responsive, loud and plays very nicely with bare fingers. Not one for a raucous kitchen party though. The numbers by themselves don't tell all. The trick, I think, is to let the numbers be an indicator to help steer you where you wanna go. I think building technique and skill/craftsmanship play a huge roll. I think someday I will build the perfect guitar. I also think, that because I think that way, that day will never come.  Ken |
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| Author: | George L [ Sat Jan 23, 2016 9:03 pm ] |
| Post subject: | Re: Specific Mobility |
Quote: I think someday I will build the perfect guitar. I also think, that because I think that way, that day will never come. I think that that way too ... I think. 
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