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The Top
Aside from the now famous roundback shape, the single feature that sets Adamas guitars apart from other acoustic guitars is the top. A guitar top should be strong, yet light and resonant. It's largely the flexibility of the top that determines the sound output and quality. Even the best spruce tops have their limitations. Too thick, and the tone is weak and harmonically limited; too thin, and the top can warp and crack. The Adamas top solves these limitations presented by natural materials.
Called a Fibronic Soundboard, the Adamas top is really a composite
structure, built with two .005" carbon-graphite outer layers
with a .035" birch veneer sandwiched in the center, all bonded
together at 250° F. While the fibers of the carbon run in
a longitudinal direction parallel with the neck of the guitar,
the birch veneer grain is set to a 60° angle to the carbon.
This yields an extremely rigid, yet uniquely thin membrane,
one-third the thickness of a typical spruce top. Such a dramatic
result in thickness results in a top that is much more dynamic
and response than one produced from traditional materials.
The finish itself is very light to minimize any impairment of sound. The effect of the opposing grain directions between the carbon and birch virtually guarantees that, short of physical damage, the Fibronic Soundboard will not crack.
Since there was no need to use the heavy "X" bracing pattern
on the Adamas, Ovation's engineers were given great flexibility
in developing the top bracing system. Their goal was to engineer
a system providing consistent acoustic response across the entire
playing range of the guitar. After testing and experimentation
that involved electronically measuring the instrument's acoustic
response across a wide frequency spectrum, the asymmetrical
Adamas fan bracing pattern was implemented. This system, composed
of 9 lightweight braces, each with its individual length and
weight controlled to within several tenths of a gram, provides
optimum transmission of the string vibrations across the top
with minimum restriction of flexibility. Fans and braces have
been engineered specifically for the Fibronic Soundboard to
achieve the design objective of +- 3 db change over the entire
playing range of the guitar.
Contributing to the thin, resonant top are the unique and highly recognizable soundholes of the Adamas. Historically, the guitars soundhole has been located several inches in front of the bridge. With this soundhole location, the top must be heavily braced in order to compensate for making such a large hole near to the bridge, an area of great stress due to the tension of the strings. By replacing the one large center soundhole of a traditionally designed guitar with the symmetrical series of holes in the upper bout, the strength of the top has been greatly increased and the sound dramatically improved. This relocation is indispensable to the distribution of the tension from string loads on such a thin soundboard. The pattern and size of 22 symmetrically placed soundholes was developed to minimize feedback when playing electrically at an extremely high level. Total area of these soundholes is approximately equal to that of the original round soundhole used for Ovation guitars.
The design of the Adamas cutaway models allows only one series of 15 soundholes and one epaulet. Yet, due to the decreased internal volume of the bowl, the guitar yields no noticeable reduction in overall sound output.
Ovation engineers were able to improve upon another aspect of guitar top design with Adamas: the manner in which the top is fixed to the sides. Traditional instrument design makes use of a series of wooden triangles, called kerfling blocks, between the sides and the top. This method effectively secures the top to the sides, but it also tends to restrict flexibility of the top near the point where it meets the sides, creating an area of "deadness" in the top around the entire outline of the guitar. Instead of this technique, the Adamas top is secured to the bowl by means of a specially-designed flexible "ring," which couples it to the bowl yet allows it to vibrate much more freely near the edges, thereby minimizing restriction of vibration where the top joins the bowl.
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