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AEB-2 & AUB-2 Scroll Basses
Design and Construction Details:
The Overall Design

In designing these instruments, I've concentrated on the details of the mechanical structure, and how they work together to create the sound. These instruments aren't showcases of exotic woods or museum-quality finishes. I put most of my effort into developing new methods of reinforcing the neck, better ways to lock the parts together, and tuning the stiffness of the structure to bring out the internal tone. Almost everything on the AEB-2 is custom made, including all the hardware and even the strings! The only stock parts are the strap buttons and the knobs.

The cool headstock and the strange looking body aren't the important features of this instrument. It's the unusual relationship between the strings and the structure that make it different from other basses. The AEB-2 (and the original AEB-1) use strings that are about 4" longer than normal, because the tailpiece is separate from the bridge, and is mounted at the very back edge of the body.

The purpose for this is to allow the strings to be plucked more aggressively. Because there is more length of string to be stretched, it can be pulled farther to the side with the same amount of force, while keeping the string's overall tension high to get the best tone out of it. As the string snaps back, it develops a longer, more dynamic attack at the beginning of the note.

AEB-2/AUB-2 Specifications:
Scale length: 35"
Overall Length: 48"
Body Width at Lower Bout: 14 1/2"
Body Thickness: 1 1/4"
Weight: 10 lbs to 10 lbs 4 oz.
Fingerboard radius: 7 1/4"
Neck thickness to surface of fingerboard:
0.800" at 1st fret
0.900" at 12th fret
Neck width:
1.75" at zero fret
2.45" at heel
Number of frets: 20 + zero fret
String Spacing:
1.32" at zero fret
2.25" at bridge
String Dimensions:
40 1/4" from ball end to nut block
45" overall length

On the fretless AUB-2, this provides the percussive pulse to each note that is the true character of the sound of an upright bass. Played hard with the tone control rolled off, the AUB-2 has the best upright-like tone of any horizontal electric bass that I know of.

On the fretted AEB-2, plucking hard adds a sharp punch of overtones and subharmonics to the note. The combination of the long strings and the AEB-2's unusually resonant structure give it a very clear sustaining tone, but without the coldness of a composite or metal necked bass. As described in the section on strings below, the AEB-2 was designed to use flatwounds, and they sound much clearer and brighter than flatwounds typically do on most electric basses.

In designing the structure of these instruments, I deliberately made the two ends where the strings are anchored very stiff and solid, while the portion in between is divided into two sections that I've separately tuned to bring out the tone that I want.

At the headstock, the strings bend sharply over a brass block that is anchored directly into the truss rod structure. Also, the scroll style headstock is inherently stiff in the vertical plane, as compared to a standard headstock, because of the vertical sides. It's not all for looks! At the other end, the bridge, tailpiece, and the brass bars that are embedded in the body are very stiff and heavy. These features solidly connect the strings to the structure, adding sustain, clarity, and a wide overall range to the instrument's tone.

The structure between the two ends serves to shape the tone, as an EQ would. In my experience, the stiffness and damping of the neck and neck/body joint mostly affects the low and low-mid frequencies. Making the neck very stiff tends to bring out clarity and punch on the bottom end, but the tone may become cold or synthetic sounding. Reducing stiffness or adding damping by using softer woods will make the tone warmer, but it will reduce the instrument's clarity and frequency range. All luthiers work with these factors to find a good compromise.

On the AEB-2 and AUB-2, I've taken a different approach to balance stiffness and damping with an unusual arrangement of the internal structure of the neck. The truss rod itself is very heavy, and is encapsulated in a bed of epoxy and raw carbon fiber strands. Unlike most basses, the truss rod is sunken very deep into the back edge of the neck, where it is under tension from the bending loads of the strings. The front portion of the neck, which is under compression, is all wood. With this combination, the high stiffness of the back of the neck provides the clarity and punch, while the compression of the wood on the front of the neck adds enough damping to bring out warmth without cutting the clarity or frequency range.

The other part of the structure which affects the tone is the portion of the body between the neck pocket and the bridge, which seems to mostly affect the high and high-mid frequencies. The unusual design of the AEB-2/AUB-2 body, with the two big F-hole cutouts, tends to isolate the center area of the body that carries the structural loads, making it easier to adjust its characteristics. Softening it brings a "sweetness" to the high end; a widening of the fundamental spikes that is similar to warmth on the bottom end. If it's too stiff, the high end is very clear, but is cold sounding. The key is to find a balance between sweetness and clarity of the high end. During the development process, I experimented with different woods for the body, like ash, maple, mahogany, and koa, and several methods of construction.

The best combination, which is used on all the production instruments, is western white ash with a series of hollow chambers routed into the top and back before they are glued together. By working with the size and shape of the chambers, I was able to get a good mix of high end sweetness and clarity, without losing the low end punch and low-mid warmth.

These two prototypes were built with mahogany bodies to experiment with the effect on the tone. AUB-2 #012 on the left has a Honduras mahogany body, and AEB-2 #021 on the right has a very light weight Phillipine mahogany body.

A side view of the AEB-2/AUB-2 headstock, finished in the classic red/black sunburst color scheme.

A side view of the AEB-2/AUB-2 headstock, finished in clear Tru-Oil.

The tailpiece of the AEB-2 and AUB-2 is set into the back edge of the body, similar to the AEB-1, but in a stronger and cleaner design. The tailpiece is mounted on two brass bars that extend deep into the body.

The bridge is machined from aluminum, and the two mounting studs rest in pockets in the front ends of the brass bars inside the body.

This is an optional ebony part which takes the place of the standard chrome bridge cover, for players who like to keep their hand right over the bridge.