Customization
Armrest - Arm bevel
Sometimes used interchangeably, both the armrest and the arm bevel serve the same purpose, even though they are essentially two different things. Their aim is to address the sharp corner where the right arm of the player rests on the lower bout of the guitar body, making it more comfortable. The main difference between both is that the armrest is an attachment to the guitar while the bevel is a cutout carved onto the body of the instrument itself. Armrests can be glued on finished instruments or can even be removable. Some guitar makers offer magnetic armrests that are detachable. For this, some level of preparation needs to be done at the interior of the body.
Bevels range from tiny to big, providing varying amounts of relief at the corners, and they must be considered in the instrument's design. Well-made slight bevels should not interfere with the vibrating surface of the soundboard, thus leaving sound quality untouched. The most common bevel on classical guitars is the arm bevel, but they can virtually go anywhere around the body of the instrument, creating, for example, the so-called 'belly-cut' at the waist on the back of the guitar.
Cutaways
There is a number of different designs of cutaways possible on a classical guitar. Even though not traditional to the instrument, a cutaway is a feature that has gained popularity and contributes to the use of nylon-strung guitars in a wider range of music genres. In general, there are two main types of cutaway: the Venetian, where the cutaway is achieved through a bend in the wood, forming a rounded profile; and the Florentine, where a new section of wood meets the shortened side rib to form a sharp pointed tip. In any iteration, a cutaway serves to give the player easy access to the higher registers on the fingerboard.
While most cutaways change the outline of the guitar, it is also possible to maintain the overall shape by introducing a 'semi-cutaway', also called a 'half-cutaway', in which the cutout is made at an angle so as to not reach the back of the guitar. It is a bevel, in principle, but a rather deep one. Any cutaway means an effective portion of the volume of air inside the body of the guitar is reduced, which in turn could theoretically influence the final timbre of the instrument.
Soundport
Soundports are designed having in mind giving the player direct feedback on the higher spectrum of frequencies. Higher frequencies behave and spread differently than lower frequencies from the guitar, commonly 'projecting' strongly directly at the audience, while the player may rest with a 'warmer' impression of the sound. Then, a direct channel into the body facing the player provides them with a sound richer in higher frequencies, in theory matching more closely what is being radiated to the audience. This can be done for personal preferences, but it is also useful in live performances where monitoring is poor or there is concurrent noise.
Soundports do change the timbre of the instrument, rising its main air resonance. For this reason, they must be included in the instrument design.
Elevated fingerboard
Growing in popularity, an elevated fingerboard is an alternative to the implementation of cutaways to give better access to higher fret positions. With this feature, the base of the fingerboard is not on the same plane as the soundboard but elevated over an extended piece of the neck (thus the name).
Overall, an elevated fingerboard does not provide the same access as a cutaway but, on the other hand, the body and the soundboard of the guitar are unchanged. There is debate whether the increase in string high over the soundboard and the slight change in the break angle of the strings over the saddle affect the sound. Even if it does to a perceivable extent, it does not seem to be in a detrimental way.
Adjustable Neck
Adjustable necks on classical guitars are not a novelty. Advanced as they seem, they predate steel strings and electrical guitars. Mechanisms like the one devised by the famous Viennese guitar maker Georg Stauffer date back to mid 19th century and made it possible for the neck angle to be adjusted by the turn of a key.
It is not hard to understand why such a feature is practical. Traditionally, the classical guitar neck's angle is set during construction and cannot be tampered with later on except by extensive and intrusive work, either by a neck reset or the planning of the fingerboard. If either the neck or the soundboard doesn't hold stable enough, with time action will become too high. Besides, classical guitars are very sensitive to changes in ambient humidity, making the action fluctuate during seasons or changing environments. Traveling musicians might face this issue very often.
Sonically, there seem to be no major drawbacks from an adjustable neck. There is some debate about how it affects sustain because the neck is not glued to the body of the guitar, as normally would, but no consensus, whatsoever. There are some outstanding guitars with adjustable necks being played by professionals at the highest levels.
Some builders prefer to change the design of the heel of the guitar to accommodate the mechanism better, and the adjustments are done from there. I put myself among them. Others prefer to have the adjusting screw accessible through a small hole in the soundboard at the higher frets. Others even hide it under the fingerboard, to be accessed via the soundhole. With an adjustable neck, it is not possible to use the Spanish neck joint without major adaptations.
Adjustable Truss Rod
Contrary to somewhat widespread belief, a truss rod does not operate by changing the neck angle, but rather by changing the amount of relief, or curvature, it presents. Relief in the neck or the fingerboard is important to keep the action as low as possible without buzzing. In its vibrational cycle, a string travels further up and down near its center, which is in a guitar exactly at the 12th fret. In this area, it needs to be more clearance for the movement of the string than at the first frets, where string travel is minimal. Thus, a well-set fingerboard is not flat but rather slightly concave. In western and electrical guitars, this curvature is set by the tensioning of a truss rod. It can then be adjusted whenever needed. In classical guitars, the fingerboard itself is worked concave, and the relief is permanently set.
Generally, truss rods are not considered crucial in classical guitars. The amount of tension the nylon strings exert at the neck is smaller compared to steel-stringed instruments. It also has a ticker neck, that remains stable enough that only small adjustments in saddle height are sufficient to keep good string action through a prolonged time. After long, however, the necks of classical guitars are known to distort, and a truss rod, although would not keep it from happening, could reduce its effect on action to some extent.
I do not normally fit my guitars with truss rods but I am open to do it if requested.
Scale Length
Different scale lengths are not a modern feature. Indeed, it is only in recent times that the scale length of classical guitars has become 'standardized' at 650mm. Historical guitars range anywhere from 600 to 670mm, most commonly from 630 to 660. Nowadays, it is possible to find 640mm guitars relatively easily, but seldom shorter, except for historical replicas. Longer scale lengths are even less common.
The scale length has a significant impact on how a guitar sounds and feels. Longer strings need more tension to get to the same pitch than shorter ones, thus providing more energy to move the soundboard at the expense of being harder to play. Because of that, shorter-scaled guitars can feel easier on the fretting hand if properly set. The difference in energy transfer does not necessarily mean noticeable changes in volume, but certainly affects timbre. Shorter-scaled guitars also tend to be smaller instruments overall, which influences how it works as a whole, especially at the lower frequencies.
At the moment I offer all my guitars at the standard 650mm. Other scale lengths on demand.
Radiused fingerboard
Rounded or radiused fingerboards are a common feature in Western and electrical guitars. Players that come from that background sometimes feel that the flat fingerboard of classical guitars are not so comfortable to play. Even a very slightly radiused fingerboard can make playing feel much different for these players, sometimes combined with a smaller string spacing and thinner neck. The saddle needs to be equally radiused to maintain proper action in all strings