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 with a very thin soundboard 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, 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.
In order to implement this soundboard, we had to move to a spherical soundboard, rather than a traditional heat bent plate and adapt the body and neck geometry to maintain a suitable bridge height and action.
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 were characterized before finding the right one for this mandolin.
The soundboard bracing was developed in order to withstand the force exerted by the strings on the bridge (approximately 100 N or 10 Kgf). 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.
The resulting instrument is characterized by a spectrum denoting high monopole intensity and low content of high spatial frequency modes