Lattice Strutting Design
There are many ways of designing the interior of the classical guitar. During the 19th and most of the 20th century, the sound box was seen as a single element, made from various species of wood that all vibrate when activated by the plucked string - this multitude of vibrations would contribute 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 much of the energy produced by the plucked string is lost as it moves into the back, sides and even the body of the guitarist.
Later 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 small struts to give support. At the same time, the back and sides are made much more rigid, in an attempt to reduce the amount of energy lost into these parts, and to aid further 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 very 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 truly traditional 'guitar sound', at the same time having greater projection, 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 extremely 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 a true lattice guitar are:
Soundboard between 1.0mm and 1.3mm
Nine struts each way (eighteen in all), 2mm to 2.5mm wide, finishing at 5.0mm to 6.0mm tall
2.5mm x 1mm carbon fibre strips on top of nine struts, covering the exposed half-lap joins
Sides 1.8 mm for bending, then laminated with two layers of 0.6 mm veneer inside
Back 3mm to 4mm, then laminated with two layers of 0.6mm veneer at right-angles to each other
Neck from a hard, dense wood like walnut or maple, reinforced with a carbon fibre rod
String height at the saddle 10.5mm to 12.0mm (treble to bass)
A lattice guitar soundboard under construction