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| The violin, the mandolin, and acoustic optimization copyright 2005 Stephen Perry No reproduction allowed |
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| Tuning, Finishing, Dedamping, and Whole Body Adjustment |
Top and Back Free Plate Tuning People like to bang on pieces of wood and listen to what happens. Some pretty sophisticated mechanisms of listening exist. These are fun and pretty, although one has to wonder what relevance they have to final performance. I’ll divide these into vibration mode pitch setting, vibration node manipulation (two related processes), and zone tap tone systems. I’ve used all of these on violins. They all “work” in that the resulting instruments work, but I’m not convinced blind reliance on any single system is a secret for consistent results. With the possible exception of one described in a recent paper. I’ll try that one for a while and see how it works. First, a description of free plate modes. Some areas of a free plate move lots, some hardly at all. The area without movement is a node for that vibration mode. Different modes take place at different frequencies. We generally look at 3 modes, although I’m thinking one or two are enough to give most of the useful information. Mode 1 nodes form a cross pattern of nodes on a violin plate. Mode 2 nodes form an X. Mode 5 forms a ring. For violins see http://www.phys.unsw.edu.au/~jw/chladni.html Various makers use this approach for mandolins: see, e.g. http://wind.prohosting. com/mrnelson/mandolin/mando6.htm I’m far from convinced that free plate manipulation gives more than general information about a plate. Certainly some fine hand made violins exhibit pretty patterns, but this is just an indication that whatever work was done made the plates work nicely when vibrated. It doesn’t suggest that working from free plate patterns is the optimal path to an effective musical instrument. Pepper makes one sneeze, but it isn’t a cold. I look at the Chladni patterns as symptoms, not as the disease! Regardless, making plates vibrate glitter is lots of fun and I highly recommend it for entertainment. The ring mode is especially nice on a lively plate. One can blow glitter 5 inches off the plate sometimes. Always impressive! One can work with information on the pitch of the modes simply by graduating until the modes form a certain consistent relationship. For example, X and ring modes are an octave apart. Or one can set particular modes in top and back a certain distance apart. This doesn’t require anything but a good ear, a reference pitch, and knowledge of where to scrape to get one mode to move more than another. One can also work to get the right kind of pretty shape. In violins I notice a standard arching and graduation gives a pretty shape even if the plate seems sort of dead and needs more work. So pretty shapes alone aren’t the ticket. I tap plates and rib assemblies extensively to find and fix spots that seem dead. The plates liven up. I think of this as preparation for post assembly optimization. If I built mandolins, I’d do the same thing. Finishing systems Mandolin makers don’t seem to do much about these. The two categories appear to be nitro and varnish, without much regard for what varnish is. In contrast, traditional violin finishing systems up to perhaps 1800 likely followed the Byzantine system that evolved from Roman techniques. This system spread throughout Europe. I’ve been privileged to closely examine work from Byzantine times up through the classical period of violinmaking. Very interesting. A brief summary with observations: # 1. Wood treatment, see above # 2. Sealer, to prevent penetration of the ground (e.g., plant gum) # 3. Ground, to prepare the surface for finish (e.g., gesso or mineral filler) # 4. Paint or other colored finishing material # 5. Transparent overcoat Technique is as important as or more important than material for some of these layers. While violinmakers tend to worry about the whole finishing system in detail (at least some of us do), mandolin workers mostly look to the material itself. I think much can be done to make mandolins work differently and maybe better through consideration of the entire finishing system. Acoustic Adjustment via Structural Modification Post assembly adjustment by removing substantial amounts of wood works. No doubt. Things change when big chunks are scraped or planed out. I tend to do all the major work beforehand on my instruments. However I’ve had plenty of factory work apart to fix this and that. Often I find things done in ways obviously not so good. Irregular thick graduations, fat braces. I’ll fix this stuff. Sometimes I’ll go through and rework the plates completely by my approach. And on violins replace or recut the bass bar. The violins work better afterwards, at least according to my clients. But this isn’t really all that viable for most instruments. Invasive, expensive, unnecessary. Acoustic Adjustment via Dedamping Pretty much proven. Vibrate an instrument for a while, it “opens up.” I do this in a vibration torture box. Not really very complicated. Another helpful approach is to massage an instrument. Carefully. Very carefully. Flexing the plates can have a quite powerful effect on break-in time and open sound. Vibration approaches range from simply placing an instrument in front of a speaker through vibrating the entire instrument violently on a table. Acoustic Adjustment via Whole Instrument Tuning Martin Schleske (http://www.schleske.de), Carleen Hutchins (http://www.newviolinfamily. org/cmh/cmh-modechart.html and http://www.catgutacoustical. org/research/articles/modetune/), and Deena Spears (http://www.singingwoods.org/books.html) among many others point out the performance boost available by tuning the entire body of an instrument. Schleske’s work shows that at some relatively high vibration frequencies small areas of the instrument are moving a good deal, probably producing most of the sound. A thorough investigation of his site will likely prove most illuminating. Hutchins pointed out that the bending resonance of the entire instrument is an important control on response and feel. See the mode chart referenced above. She suggested matching this bending moment frequency she called B0 (B zero) to either the Helmholtz resonance of the sound chamber (A0 or to “Wood Prime.” Her explanation of the result is that the match “adds vibrational energy and spreads out tone over a wider range (i.e., lowers Q), thus affecting whole instrument.” Spears built on this idea by suggesting matching to the frequency that lights up the box when sung into the F hole, which is not the same as the Helmholtz resonance. That’s what I do with violins. Unfortunately, the main control on violin B0 is through manipulation of fingerboard mass and stiffness. We don’t have that control over mandolins. However, B0 adjustment works on mandolins. Roscoe Morgan still mentions he misses the lump of clay on his headstock, a temporary B0 adjustment technique! The mandovoodoo™ acoustic blueprinting process builds directly on this work. |
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| The mandovoodoo™ process was invented by and is only performed by Stephen Perry of Gianna Violins, the world's premier seller of fine Eastman Mandolins. Copyright © 2005-7 Stephen K. Perry. No use without written permission. By viewing you agree to all site terms and conditions. mandovoodoo.com (tm) is a division of Gianna Violins. |
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