The top, like the back is made up of two book matched pieces of timber. These are sanded
to close to the final thickness (approx 3mm) and joined together. The joined top is then
cut to shape and the channel for the rosette is cut out and the rosette inlaid. After a suitable
drying period, the top and rosette are sanded to the final thickness, approximately 2.5mm.
The struts are then prepared and glued into place. There are many strutting patterns used
today varying from the standard 7 fan Torres pattern to a Radial pattern shown in these picture,
to the lattice pattern used by many Australian makers. Each patter produces its own characteristic
sound. At this point the weight and stiffness are very important and these factors need to
be adjusted to optimise the output of the top and thus the guitar.
The struts are glued on to the top with the aid of a vacuum clamping rather than the traditional
clamps or Go bars. Vacuum exerts a far more even pressure along the whole length of the strut
than clamps or Go bars. The top is then allowed to dry again before continuing with the following
stage of joining the top to the sides. This is important if water based glues are used. It
is of great importance that stresses are minimized during the construction of the guitar.
The wood is very prone to absorbing moisture and changing dimensions during this stage of
construction. Prior to joining the top to the sides, the top is again weighed, flexed and
tapped to determine that the stiffness of the top is what is required. Tap tones are also
used to "tune" the top's behaviour.
Now the top is ready for acoustic testing and adjustment. This is done with an audio oscillator
which generates single frequencies and these frequencies generate the Chladni patterns pictured
here. These patterns are referred to as modes and it is the placement of these modes and
their output that is the crucial part in determining the final outcome of the quality and
character of each guitar. The first set of modes occur in a well defined series and are fairly
easy to predict and produce. Modes above about 800hz occur close together and are prone to
interference by other modes of similar frequencies. It is difficult to separate many of these
higher modes.
The testing of hundreds of instruments with the aid of computer analysis of the data allows
me to accurately predict and alter the sound characteristics of the guitars I make. This
testing and adjustment is used in conjunction with the traditional methods of using tap tones
and flexing the top. Flexing the top is important to determine the strength of the top and
its reaction to string tension. If the top is too strong the guitar will not be powerful
enough. It may sound Ok, there will just not be enough of it and it will have a closed nature.
If the top is made too week it will collapse under the sting tension and eventually the top
will become concave or S shaped and this may effect the action. Guitars that are too weak
are often powerful, but can have an unpleasant sound. They also tend to loose much of their
character in a short period of time and sound "dead".
