The advantages of a traditional top combined with those of a sandwich top ( double top).

In a system such as the soundboard of a guitar, the resonance is determined by the stiffness and mass of the wood.

With a traditional asymmetrically constructed soundboard, the thickness on the treble side is greater than on the bass side. We have more mass on the treble side, which gives us better cross-diple modes.

Most sandwich sheets are made in a 2.5D environment. Three layers; an inner core, usually a light material such as nomex, balsa,... surrounded by two layers of wood of approximately 0.5 mm thickness.

If we want this type of soundboard to be asymmetrical, i.e. thicker on the treble side, only the stiffness of this area will increase. The mass of the inner core is too small to have a major influence on the resonance, while the mass is of great importance for the sound richness and sound quality.

Suppose you could make a double top from a traditional soundboard without using an inner core.

How?

We can do this by sawing a soundboard set into two pieces. After gluing and sanding the parts, we have two very thin, identical plates.

This forms the basis for our newly composed top.

On both parts we mill parallel tracks in three dimensions by using a cnc router ( A cnc router is a mechanical divice controlled by a computer which can operate in three dimensions at the same time). So on the treble side there will be routed away less wood than on the bass side.

The center of gravity is at the point of the bridge on the high side. At this point the stiffness and mass are greatest.

The plate is then also thinned slightly towards the edges.

By gluing both plates together with skin or PU glue, a three-dimensional, asymmetrical sounding board is created ('Double top' in 3D).

This procedure is also possible in case we use an inner core of Nomex or even solid wood ( Lattice innercore). On the treble side, the plate will be milled out less deeply.

Now we know to what extent the maximum of a double top can be achieved, it might be better to combine the benefits of a traditional top with those of a double top.

If we change the start depth point on our cnc router to a higher position, the slots will overall be milled less deep, so we retain more wood. By this we can decide for ourselves in what proportion we will build 'traditional' versus 'double top'.

Double top 'parallel tracks'

Double top ' Nomex'

Double top 'Lattice innercore'