Lattice Strutting Design
There are many ways of designing the interior and the plate thicknesses of the classical guitar. Conventional wisdom viewed the sound box as a single element, made from various species of wood, that all vibrate when activated by the plucked string; - this multitude of vibrations contributes to the overall timbre and projection of sound produced by the sound box. There are many advantages to this approach, but one of the problems is that some of the energy produced by the plucked string is lost as it moves into the sides, back, neck and even the body of the guitarist.
Late in the 20th century, some makers began experimenting with a different approach to sound box design; - the idea here was to make the soundboard (traditionally up to 2.8 mm thick), much thinner than before (now as thin as one millimetre) and supported by an interconnecting lattice of slender struts to give support to this fragile top. At the same time, the back and sides are made more rigid, in an attempt to reduce the amount of energy lost into these parts, and to encourage the reflective projection of sound out towards the listener. Sometimes an armrest (fixed or removable) is also used, both for comfort, and to prevent the player's arm from damping the soundboard.
There are many variations on this 'lattice' approach, the most extreme sometimes being criticised for being too 'banjo'-like, with a piercing sound but little sustain and a loss of the traditional warmth of the Spanish classical guitar sound. With careful use of wood, thicknesses and interior support, it is possible to create a guitar with a traditional 'guitar sound', at the same time having greater projection, with good balance across the bass, mid and treble ranges, and simply being a greater pleasure to play.
This type of guitar is more demanding to make, as it involves many more steps in the construction process, and bringing the soundboard down to the membrane-like thickness required, takes great control of tools and materials. It is helpful to have the use of a 'MagicProbe' or similar device for measuring the soundboard thickness, because the traditional luthiers' dial caliper is not accurate enough.
So the essential characteristics for this type of lattice guitar are:
· Soundboard between 1.0mm and 1.3mm maximum thickness in the lower bout, and up to the lower harmonic bar; 2.0mm to 2.5 mm in the upper bout.
· Eight or nine struts each way (sixteen or eighteen in all), 2.0mm to 2.5mm wide, finishing at 5.0mm to 6.0mm tall, tapering down slightly towards the edges.
· 2.5mm x 1.0mm carbon fibre strips on top of nine struts, covering the exposed half-lap joins. (This provides the ideal rigidity - carbon fibre on all struts is too rigid.)
· Triple Sides: 1.8 mm thick for bending, then laminated with two layers of 0.6 mm veneer inside. Triple Back: 2.5mm to 3.0mm thick, then laminated with two layers of 0.6mm veneer at right-angles to each other. (This makes for a reasonably rigid back and sides, but not total rigidity. Thus the species of wood for the back and sides is important - hard, dense wood like Rosewood or Wenge, produce a sharper, more piercing sound, whereas softer, lighter species like Walnut, Maple, Mahogany, fruit woods, produce a smoother, more mellow sound. (Often the back will not be flat when the clamps are initially removed after laminating. Provided it is kept flat, clamped between some battens above and below, the flatness will return once the glue has fully dried. Using quarter-sawn wood for the back is best. )
Extra mass on Sides: Additional vertical struts can be glued to the sides internally to add mass to the sides. For example, ten struts placed evenly around the sides (five on each side) can add 100g to 150g. This produces more note separation to the sound, and less mellowness.
· Neck from a hard, dense wood like walnut or maple, not cedrella, reinforced with a carbon fibre rod
· String height at the saddle 9.0mm to 10.0mm for first string and 10.0mm to 11.0mm for sixth string. Or taper the bass side of the fretboard so that the saddle height is similar from 1st to 6th strings - about 10mm.
· 'Rosette' string beads or similar are recommended to be used to maximise the break angle from saddle to bridge hole, for clarity of sound. Bridge string holes can be drilled higher from the base of the bridge than with conventional knot tying, indeed, care should be taken to not exceed a 45 degree angle from saddle to hole, and to make the saddle surface very smooth and angled downwards, to ease the string and avoid stress on its change of angle.
Click here to listen to this guitar
(Yvonne Bloor playing recorded without any editing or modification.)
A lattice guitar soundboard under construction