DF - Carbon
This mandolin, as for the classic DF model, was developed from DF-style mandolin of luthier Federico Gabrielli, during the research project Choice of wood in musical instruments: Italian Red Spruce and traditional mandolins, funded by World Wood Day Foundation in 2019.
Despite its classic look, this instrument was developed aiming at an unparalleled sound intensity and sustain. These are achieved by a peculiar soundboard design with composite bracing, a technology that allows to hinder high order vibration modes and improve the radiation efficiency resulting in high volume and exceptional sustain.
The materials used for the construction are completely characterized before assembling to guarantee the maximum acoustic throughput and long term reliability.
In these videos, professional musician Talia Elisa Benasi performs some themes to compare classic DF and DF-Carbon mandolins.
DF - Carbon: an innovative Italian mandolin design
The idea lying beneath this project was to realize a composite lattice bracing soundboard for a traditional bowlback mandolin. The bowl back, despite being made made of thin ribs, is a very tough and rigid structure due to the pronounced curvature and, technically speaking, can be considered a so-called “shell”. Shells have very high vibration frequencies and do not couple with the soundboard, an advantageous effect, allowing the sound to radiate efficiently, without being dissipated on the player’s body.
This configuration is hence the best one to test experimental soundboard configurations, such as carbon fiber lattice bracing.
DF-Carbon soundboard is spherical, rather than a traditional heat bent plate. The radius of curvatre gives a similar stiffness but without compromising tonal and structural qualities with no compromise for the musician.
Sundboard thickness based on wood characteristics
The sounboard thickness is calculated considering the orthotropic wood properties in terms of elasticity and damping. These properties are characterized by six different acoustic measurements for each piece of wood. Several spruce samples are characterized before finding the right one for this mandolin.This technique allows us to select only the best wood.
Imagine to push down on the soundboard with a force of 10 kilos: now you have an idea of how much pressure is exerted on a mandolin soundboard.
This force provides such a high stress that traditional balsa/carbon fiber bracing would quickly fail, making the instrument not reliable in the long term.
We hence had to design special spruce/carbon fiber bracing with an adequate resistance, but with a very low mass, a difficult challenge where we succeeded thanks to calculations and experiments.
Optimized soundboard vibration modes
The sound is characterized by an extremely efficient mode of vibration called monopole. This mode transforms the strings vibration into sound waves that diffuse in the surroundings with large volume and sustain.