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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
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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 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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