Design and Construction
Dual Fan Struts (Latticed)
I'm sure most would agree that the top of a guitar will govern its performance characteristics more than any of the other components. While the manner in which the other components are designed and constructed can make an important contribution to a guitar's response, their role is primarily to support what the top is sonically capable of producing.
The principles governing the manner in which a top operates are extremely complex. Essentially they revolve around two opposing characteristics that govern its ability to vibrate in response to applied energy. The first is "impedance" (the extent to which the top resists vibration) and the second is "admittance" (the extent to which it responds to vibration). Tops with too much built in impedance will not produce much volume or projection. Tops with too much admittance can be loud and projective but may sound unpleasant as they respond excessively to a wide range of harmonic partials (overtones). So the apparent challenge seems to be finding the balance between impedance and admittance that will produce the desired guitar like sonority and tone along with the needed volume. But its far more complicated than that.
The challenge described above might not be too difficult were it not for the fact that the "mode" (manner or pattern in which the top vibrates) is different for each frequency or pitch that the top is called upon to respond to. This means that the top vibrates in a different mode for each note that can be played on the guitar. For lower frequencies, the top tends to move up and down as one unit. As progressively higher notes are played the top will be divided into increasingly smaller and more numerous vibrating segments. If you are interested, you can see some animated diagrams below that illustrate this somewhat.
Added to this complication is a requirement for the top to respond to more than one note at a time as in chords and polyphonic lines of music. This means that the top is required to vibrate in numerous combinations of modes all at the same time. So, the challenge is to find a bracing design that provides the best compromise in terms of combined balances of impedance and admittance for all of the notes that are available on the guitar. At the same time, the design should produce the guitar-like tonality that originated in the instruments of Antonio Torres and the masters who succeeded him.
A lattice bracing design with its pairs of long parallel struts that intersect in numerous places divides the top into much smaller sections than a simple fan bracing system. As a result, I believe a latticed braced top can be more "friendly" to a higher number of modes including combinations of modes that result from combinations of notes played concurrently.
However, if the top is built too lightly, the unpleasant characteristics that I mentioned earlier can become a problem. But even if the top is built to achieve a reasonable balance between impedance and admittance, the instrument may still not produce the desired guitaristic tonality. Structuring the pairs of struts into a focused fan configuration seems to overcome this problem.
These are the concepts that underlie my current design. In my latest configuration I adjusted the manner in which the heavier and lighter braced were laid out so that the stiffness in the top is distributed more symmetrically and radially from the center (where it is needed the most) toward the outer edges where the top needs to be more flexible. I am very pleased with the further improvements to the balance that resulted from my latest evolution.
When you introduce the musicians' personal preferences into the equation, you find that what I've said up until now, doesn't cover the whole challenge. Different people look for different things in a guitar's characteristics. Some like an instrument that is bright and percussive. Flamenco players might fall generally into this group. Others like an instrument that is deep and mellifluous. Some place power and projection at the head of their wish list. Others look for the widest possible range of available tone colors. Then there is an overriding concept I recently learned of dubbed "psycho acoustics" which describes the tendency of people to initially hear what they want to hear from an instrument rather than what the instrument really produces. When the "psycho-accoustic" state has run its course they may find themselves with an instrument that they are not really happy with. It is for this reason that I offer a 30 day trial period during which commissioned guitars can be returned for a full refund.
I, as a luthier, am (of course) subject to personal preferences myself. If I were not, I doubt that I could pursue the activity with any real conviction. Accordingly the development of my guitars has been governed by my own preferences. Over time these preferences have become increasingly refined and discriminating and I would like to think that this is reflected in the quality of my instruments.
So, these are the some of the main challenges which I hope I have described as concisely as possible for those who are interested. For the others, I apologize for any perceived lack of brevity. Going forward, I happily continue to wrestle with these challenges. I say "happily" because I feel that I've been able to make progress and continuously improve my instruments from the perspectives of my own preferences and those of an ever growing number of diverse clients some of whose testimonials I have included in this site.
A Plea For The Traditional Construction of Classical Guitar Sound Boards - Sebastian Stenzel, Luthier
"The Virtual Guitar" http://www.phys.unsw.edu.au/music/guitar/virtual.html
|Low Frequency mode||Mid Frequency mode||High Frequency mode|