Designing and Building A “Simple Machine”
First and foremost, a stringed instrument is a “simple machine” which serves in function to transform the mechanical
energy of its vibrating strings into audible sound. The synergy of components, craftsmanship, and creativity that goes into
it is what gives each instrument its own unique personality. Many factors influence and affect form and funtion making these
"simple machines" actualy quite complex.This is why I believe creating an instrument that is truly enjoyable and gratifying
to play is as much an art as it is a science.
Wood
I like to think of the wood in a bass as a "tone effect". Each species of wood has its own physical properties which cause
the wood to filter and transmit vibration in a unique way. This imparts a distinctive tone (timbre) to the instrument’s
sound.Two of the key factors affecting wood’s tone are stiffness and density. The stiffness of wood affects its ability
to transmit vibration while it densitiy affects its ability to dampen vibration. Since these are contrary effects, the stiffness-to-density
ratio is what's important. A case in point is the contrast between Ebony and Maple. Both popular fingerboard materials known
for their bright, clear tone. But Ebony has a lower stiffness-to-density ratio (even though it is actually stiffer and denser
than Maple!). As a result, Ebony provides more vibration damping than Maple, especially in the mid-range. Ultimately Maple,
with its higher ratio, is more efficient at transmitting sound (vibration) over a wider frequency range,while Ebonys superior
stiffness and density help to facilitate a strong low fundamental which can be harder to achieve using maple. To some
degree this can be discerned through observing a woods tap tone.
This same principle applies to the tone of neck and body woods as well. The bottom line is, much of the strings’ vibration
is influenced by the wood used in constructing the bass and vice versa. This offers a golden opportunity to tailor the instrument’s
sound by choosing a specific mix of woods for the neck, body, and fingerboard.
Old standbys like Ash, Alder, Maple, and Mahogany are fairly consistent within a species in terms of their color, weight,
and tone, but regardless of species there is always some variation to account for. The list of suitable woods is quite extensive,
ranging from native Oregon Myrtle to exotics like Cocobolo or Padauk.
In a way, accounting for the tonal effect of the wood is like deciding which stompbox to put first in an effects chain. It
doesn’t make sense to put an EQ that cuts the treble ahead of an effect that boosts it. Similarly, it there is no point
in choosing woods that tend to dampen a frequency range that you’ll need to amplify later.
Of course, the type of wood alone doesn't tell the whole story. Where a particular piece of wood is used on the bass is important,
as is its size and proportion, as well as other factors.
Neck Features
Neck Joints
The neck-to-body connection is a critically important part of bass guitar design. There are three basic types of neck
joints in common use today: neck-through, bolt-on, and set-neck.
The neck-through design is best known for superior sustain due to its monolithic construction. Both ends of the strings
are attached to one continuous “beam” that runs from the headstock to the end of the body. With no voids
or joints to absorb string energy, neck-through construction is an effective delivery medium for sustain. Compared to the
other neck joining methods, the body wood plays a less prominent role in the overall tone of the instrument because the body
wings have essentially no direct connection to the strings.
Bolt-on neck construction allows the neck and body to share a more balanced influence on the instrument’s tone
and feel, creating a characteristic punchiness. The neck is a separate component that resides in a pocket cut into the body,
secured from the back by bolts. There is no glue or other bonding. The bolt-on architecture, though cost-effective, trades
off a certain amount of sustain. String energy can be lost in the neck/body joint, particularly if the two components do not
fit tightly.
The set-neck method combines the best qualities of each of the other two designs. This type of joint is my personal favorite,
used on the majority of the instruments I build. A long neck heel mates to a precisely matching wedge-shaped mortise that
extends all the way to the pickup cavity. This maximizes the contact area between the neck and the body. When glued, the joint
forms a bond that is stronger than wood for maximum stability and tonal transfer.
This tightly integrated and neck-body joint essentially fuses the two elements and provides sustain that rivals a neck-through.
At the same time, the strings can impart their energy directly to both the neck and the body, delivering the punchiness of
a bolt-on bass. The body also has its full share of influence on the sound, a major benefit in chambered or semi-hollow body
designs.
Other Neck Features
My basses include several other beneficial neck design features as standard. Truss rod access is at the heel end of the
neck, where a routed channel provides clearance for the adjustment tool. This offers maximum accessibility and a clean look,
and there is no rod cover to fuss with or lose. Putting the truss rod nut at the heel end of the neck also eliminates the
need to put an access cavity exactly where any neck is weakest—at the point where the headstock angles downward.
My headstocks are scarf-joined in order to eliminate grain run-out, the main culprit in most broken headstocks. This scarf
joint allows the wood grain to run lengthwise down the entire headstock, increasing its strength and greatly decreasing the
chance of a broken headstock.
Lastly, the body-matching top plate on the headstock is not the thin decorative veneer used on many instruments. The plate
is a solid piece of wood, 5 mm thick, which adds strength and holds the nut securely in place at the end of the fingerboard.
This combination of features makes a Helms custom bass a solid, responsive instrument with a unique look and sound.
