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| Density/Damping Correlation for Hardwoods? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=45123 |
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| Author: | meddlingfool [ Thu Feb 12, 2015 1:45 pm ] |
| Post subject: | Density/Damping Correlation for Hardwoods? |
I was wondering if you can make a reasonable prediction as to a woods damping/tap tone factor by the specific gravity. For instance, coco is listed as .89-1.1, and it rings like a bell. Walnut is .51-.61 and is quite dull in comparison. Mahogany is .52-.59. EIR.70-.83. Those numbers pretty much track very well with the amount of overtone content in the finished guitar IMO. In order, mahogany then walnut (with a lot of crossover per piece), rosewood, then coco. So I'm wondering if you looked at the specific gravity of a species if it gives a fair assumption of the potential tonal properties? |
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| Author: | Tom West [ Thu Feb 12, 2015 2:49 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
Ed: And then there is ebony and spruce..........!! Some ebonies tend to be higher in damping then you would think and of course good spruce really rings. I would think maybe Alan Carruth may have some testing along this line. Sounds like something he would do. Maybe he will show up and give us some info. Tom |
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| Author: | meddlingfool [ Thu Feb 12, 2015 4:02 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
Hope so. I'm about to be rash at the lumberyard to test my little theory... |
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| Author: | DennisK [ Thu Feb 12, 2015 4:18 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
It's not a sure thing, but does seem to be the general trend. Interestingly, softwoods seem to go the opposite way... western redcedar is ultra-light and one of the most lively of all woods, and most pines are heavier and duller. Spruce is in the middle in both aspects. Black limba is probably the lowest damping medium density hardwood I know of. Redgum is pretty good too. Movingui is one of the best tapping of all woods, and not that heavy either. And pau ferro is heavy, but pretty lifeless. Another factor is that depending on how you decide on your back thickness, it may just be that the denser the wood, the less the back moves, and thus less energy is robbed from the top. |
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| Author: | Alan Carruth [ Thu Feb 12, 2015 5:44 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
So far as I can tell, there's' not a strong correlation between density and damping in either hard or soft woods. Oak and persimmon are both quite dense, and have fairly high damping as compared with Brazilian rosewood of the same density. The African blackwood I have has fairly high damping, and would sink in water. Ditto for some of the Morado I've used. Redwood has damping as low as BRW, and high density for a softwood, while Western red cedar tends to be very light with low damping. Some balsa I've tested has surprisingly low damping; but that's a hardwood. It would be nice if there were a bunch of simple rules of thumb that you could use with some confidence, but, alas.... So far the only one I've found is the relationship between density and Young's modulus along the grain in softwoods, and even that's not guaranteed. |
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| Author: | Trevor Gore [ Thu Feb 12, 2015 6:44 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
Whilst it doesn't answer your specific question (though I'm inclined to agree with Alan) have a look at Design Section 4.3 There's some stuff there on sound radiation coefficient and log dec (damping). You might find that sound radiation coefficient is more useful to you... Damping is a pretty variable property (ask Brian Burns!), but is easier to hear than it is to measure reliably. |
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| Author: | James Ringelspaugh [ Thu Feb 12, 2015 8:00 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
My experience is that most high density woods ring well when tapped unless they are wet/green, unseasoned, or if they have cracks or a lot of small fractures. I have some Gabon ebony that rings like a bell and some traditionally low damping woods that sound like cardboard. I think there's an awful lot more variation between boards in the same species than people think. I wonder how much internal stresses play a part. An awful lot of the low density Honduras mahogany that I've come across has tapped well, almost like spruce, but similar density woods like khaya and soft maple are almost always thuddy (with notable exceptions). Sometimes you just need to wait... I've had lots of cocobolo that was pretty listless when I took it off of stickers (and was definitely dry) but a year or so later behaved like a glass gong. Maybe extractives crystalizing as the wood ages plays a part? Anyway, long story short, IMO density is a very poor predictor compared to other factors, and there's no substitute for just picking up a board and giving it a tap... you know it when you hear it. |
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| Author: | John Arnold [ Thu Feb 12, 2015 11:03 pm ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
Quote: Oak and persimmon are both quite dense, and have fairly high damping as compared with Brazilian rosewood of the same density. Dogwood is another example of high density and high damping. |
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| Author: | Eric Reid [ Fri Feb 13, 2015 12:43 am ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
I've linked to these before, but they explore the relationship you're talking about, and give some ranges of values for a variety of woods: http://www.woodculther.com/wp-content/uploads/2008/10/bremaud.pdf http://www.ecofog.gf/greybase/files/bremaud/2009/94_Bremaud_etal2009.pdf |
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| Author: | meddlingfool [ Fri Feb 13, 2015 1:26 am ] |
| Post subject: | Re: Density/Damping Correlation for Hardwoods? |
Thanks Eric! |
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