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| tonal properties of hide glue http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=2542 |
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| Author: | Dave White [ Thu Jul 21, 2005 5:28 am ] |
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I've read on countless occasions that using hide glue for top braces is best as it gives the best "tonal" properties as it "transfers more energy to the top" (and other similar reasons - it is harder and so less enery is lost etc). I know the great properties of hide glue in terms of heat creep resistance and being able to release/repair etc, but have any scientific experiments been done on the "tonal properties"? Just how much more energy loss is there in braces glued say with LMI white glue or titebond compared with hide glue and where does it go - heating up the glue or vibrating the glue? Yours curiously!! |
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| Author: | Tim McKnight [ Thu Jul 21, 2005 5:56 am ] |
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Dave: I have an article that I will be submitting to either GAL or ASIA that has quite a bit of data on glue hardness but not on tonal response. I know when I switched from Titebond to Hide my guitars sounded discernably better but I don't have any data to support that statement. I will tell you the Hide glue is the hardest of all glues that I tested and LMI's white was only one measurement number below hide glue. |
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| Author: | Dave White [ Thu Jul 21, 2005 6:08 am ] |
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Thanks Tim - I look forward to the article. Was the better sound a "step change" that you noticed with your very first all hide glue guitar and if so where there specific areas of tone or did it just sound better overall? Coming from a scientific background I'm always wary of the cause/effect and causality. I suspect that a lot of great guitar makers use hide glue and hence make great sounding guitars (as they are great guitar makers . . if you see what I mean  )
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| Author: | KiwiCraig [ Thu Jul 21, 2005 11:33 am ] |
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I've been using Hide glue for 35 years . I use others on occasions, but there really is no substitute for good old smelly hide Now if only people would stop panicking about open glue time!!.Just work methodically, go through a dummy run etc, have all clamps opened to the right width and right at hand. Warm the work! I don't have any scientific evidence on it's acoustical properties, but who cares!! Most of the great instruments have been assembled with animal glue,right?? KiwiCraig |
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| Author: | Tim McKnight [ Thu Jul 21, 2005 12:33 pm ] |
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Dave: Yes, it was a step change and was quite noticeable overall but unmeasurable. It's worth the work but if you don't want the hassles of hide glue then LMI's white glue is a very close second, IMHO. |
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| Author: | Alan Carruth [ Fri Jul 22, 2005 12:07 pm ] |
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If there is a difference I'd bet dollars to doughnuts that it's due to damping. If that's the case it would be an easy enough measurement to make: just put together samples with the same wood and different glues and vibrate them to see which ones had the higher damping. In fact, you would not even have to use wood, with all of it's inherent variability: glue some narrow strips of glass onto wide ones, and check them out. There are very few commonly available things in this world as uniform as float glass. Sure, the braces might not stick down for long, but if they hold up for the test.... |
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| Author: | LanceK [ Fri Jul 22, 2005 1:06 pm ] |
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[QUOTE=Alan Carruth] If there is a difference I'd bet dollars to doughnuts that it's due to damping. [/QUOTE] Al, I regret that I didn't have a chance to sit down and share a donut with you at ASIA - It was good to meet you though. |
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| Author: | Alan Carruth [ Sat Jul 23, 2005 9:12 am ] |
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I mentioned this to one of my students today, and he had an even better suggestion: get strips of glass that are, say, 1" wide, and glue them together. Easier than gluing on braces. I'd bet you could get glass cuttoffs at almost any hardware store. |
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| Author: | Tim McKnight [ Sun Jul 24, 2005 5:06 am ] |
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Al: What about using glass microscope slides? They would all be the same identical size which would greatly reduce variation in the experiment. |
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| Author: | Mario [ Sun Jul 24, 2005 6:25 am ] |
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Slides should be perfect. Now, how do we measure the damping? |
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| Author: | Tim McKnight [ Sun Jul 24, 2005 10:23 am ] |
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Since Al has all of the high tech hardware stuff I will nominate him. Can I have a second? |
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| Author: | Alan Carruth [ Sun Jul 24, 2005 11:33 am ] |
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The problem with slides is that they are so short: the frequency of the lowest bar mode would be very high. In some cases the damping factor might vary with frequency (that seems to be true of wood), so we'd want our test to be working in a 'normal' range. Damping is pretty easy to measure if you have the right equipment. Things with low damping only resonate at the exact 'right' frequency, while things with high damping can be driven almst as easily far off resonance as they can at the 'correct' pitch. That's one reason why the 'tap tone' of a low damping material, like glass or Brazilian rosewood, has a definite pitch, while high damping stuff, like styrofoam just makes a sort of 'thud' that doesn't convey as much of a sense of a particular tone. Things with high damping also don't 'ring' as long as things with low damping, so that gives you another way of measuring it. The way I do it is to get a little bar of the material in question and stick a tiny piece of iron on to one end to act as an armature. I have a rig twith two threads that can be moved around to support the bar at the stationary points when it's vibrating, which are usually about 1/5 of the way in from the ends. There's a coil that I can plug into my signal generator at one end, with a magnet under it, and this pushes the armature (it's just like an electric guitar pickup only backwards; making a motor out of something that we normally see as a generator). I 'listen' to the strip with a dB meter, tune the singnal generator to find the peak frequency of the vibration, and the points on either side where it's 3 dB down. At these frequencies it has half the energy of vibration for the same drive force. The difference in frequency between these 3 dB down points above and below resonance is the 'half power band width', and the Q value is just the peak resonance frequency over that band width. There's another way to do this called 'Log decrement', but I've never used it. I'll have to look it up, because it may be even easier to do than the strip tests I've used if all you want is the Q value. This sounds like an interesting test, but right now I'm falling behind on orders, owing in part to a couple of other 'science fair projects' that I've been working on. These things always look easy until you get started, and then, of course, you're caught. The project I did on string forces 'should' have taken a week: I started on it six months ago and there are still some things to clear up. This would be a great addition to Tim's article, although I could understand it if he doesn't want to dive back in at this point. If I can help out with advice and such I'd be happy to do so, but I'm reluctant to commit to anything more at this time. |
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