A Lightweight Electric Bass

Copyright © 2004 R.M. Mottola

[This article originally appeared in American Lutherie #78.]

A survey of advertisements and websites of solid body guitar and bass manufacturers turns up a number of instruments claimed to possess superior ergonomics. On the other hand, scanning the research literature turns up precious little in the way of design alternatives that offer proven ergonomic benefit. But the number of marketing claims of ergonomic superiority probably does indicate something of the desirability of improving the ergonomics of stringed instruments. And the heavy solid body bass instruments with their long necks could likely use more improvement in this area than other shorter and lighter instruments.

Although there may be a number of modifications to the basic design of the electric bass that could improve its ergonomics in various ways, my observation (also unsubstantiated, to be fair) is that reducing the overall weight of the instrument can improve its ergonomics in general. From a playability perspective, lighter just seems to be better. For this reason, any weight shaved off a bass can probably be counted as an improvement in the ergonomics of the instrument.

This was the primary incentive for me to try to put together a reduced-weight electric bass. But I can't discount the coolness factor as motivation for building a lightweight bass either. Light is simply cool, at least to me, and, as a drummer I used to work with was fond of saying, usually as she was putting on her shades, coolness is everything.

Photo 1 – Lightweight electric bass.

Now, all of this was bubbling around in my head for a while, but it took a bit of time before anything inspired me to put saw to wood and build something. That inspiration came in the form of the Parker Fly bass, a no-compromise instrument that weighs in at less than 7 lbs. As is the case with the lightweight Parker Fly guitar, the Fly bass makes use of unconventional materials and construction techniques to keep the weight down without compromising the sound. I wanted to see if it was possible to build a lightweight instrument using (more or less) traditional materials and construction. Another requirement was that the instrument should still sound like a modern electric bass. The resulting instrument, a lightweight version of my Mezzaluna (Italian for half-moon) bass is shown in the pictures. The general approach taken to reducing weight in this instrument was similar to that used in auto racing to make street cars more suitable for competition, and relies on three basic techniques: removing unnecessary components; substituting lightweight components for heavier ones; and lightening structure where that can be done without sacrificing stiffness and strength.

Deleting unnecessary components on a bass involves some tough choices, as everyone has a different idea of which components may be considered unnecessary. This instrument has no string ferrules, only one pickup, no tone controls, and no active electronics (and thus no battery). The neck of the instrument is set in (i.e., glued on) rather than bolted on, thus eliminating the weight of neck mounting screws and plate.

Pickups are heavy, so going with just one is a major win, weight-wise. I used a single Bartolini BB4C pickup in this bass. There is considerable difference in weight among the readily available bass pickups, with thinner (like Jazz Bass style), un-potted pickups generally the lightest, and thicker, potted, Musicman style pickups the heaviest. The BB4C is not the lightest pickup available but it does work well in a single pickup configuration, delivering a modern tone. A single un-potted neck-width Jazz pickup would have been the best bet in terms of weight, but the sound is just too thin in a single pickup instrument, in my opinion.

Eliminating the electronics saved a little weight, but it does all add up. Interestingly enough, deleting even a passive tone control gives the instrument a brighter, more "active" sound, because passive tone controls actually cut some high frequencies even when they are turned all the way to their most treble position.

Photo 2 – A simple aluminum blade bridge is used.

A number of lightweight components were used in place of heavier ones. Hipshot Ultralight tuning machines were used, saving a little weight over the more ubiquitous Gotohs. A plastic volume control knob is used instead of a metal one. A big weight decrease was realized by substituting a simple handcrafted aluminum "blade" bridge for a heavier machined bridge. Intonation of the bridge was set during construction for medium gauge strings, and action is adjustable with an Allen wrench from the back of the instrument.

Some lighter weight materials were used in the construction of this instrument, but nothing particularly radical. The neck is made of laminated soft maple, which is a bit lighter than the hard maple typically used. I have found this wood to be quite suitable for use in bass necks in the past. The bass is finished in hand-applied polyurethane/oil, which offers a surprising but small weight advantage over a heavy coat of nitrocellulose lacquer or polyester. Every gram counts.

Figure 1 – Cutaway end view of the body showing details of the blade bridge.

Perhaps the biggest overall weight savings came from lightening the body and neck of the instrument. Now, getting rid of some wood in a solid body isn’t too hard to do, but doing that in such a way as to maintain the physical balance of the instrument can be a little tricky. It helps to visualize the balance issue in the context of weight reduction if you consider the instrument to be a beam hanging from a balance point, that point being the strap button on the upper horn. Any reduction in weight on one side has to be addressed with weight reduction on the other. Due to the leverage offered by the beam, weight reduction at or near the ends of the beam, e.g. at the headstock and at the butt of the body, will have more of an effect on balance than would reduction at or near the balance point.

The lightening process was iterative. The first step was lightening the neck as much as possible. The neck sticks out so much in an electric bass that even the smallest weight savings in the neck and in particular in the headstock allow the builder to take off considerable weight at the body end and still retain good balance on the strap. The string spacing on this four string instrument is 21/32" - more typical of a five string, but it does make for a narrower and thus lighter neck. A small amount of weight was saved by shaving 1/16" off the thickness of the fingerboard. At the headstock, the tuning machines were mounted 2 + 2. This doesn’t save any weight here, but it does put the weight of the machines closer to the body than a 4-in-line configuration would, and thus requires less body weight to balance them. Of course a useful approach is to simply move the machines off the headstock altogether, but there are enough people who exhibit strong negative reactions to the headless look that I tried to do the job using the more traditional placement of the machines.

Photo 3 – The action is adjusted with an Allen key from the back of the instrument.

One potential design feature that could be used to effectively shorten the neck is to shift the point at which it joins the body (and the bridge position, too) into the body. Another is to simply move the point of balance by elongating the upper horn. These turn out to be problematic for a particularly subtle ergonomic reason. Players’ sense of where they are on the fingerboard seems to be affected by where that fingerboard is, relative to the rest of their bodies. This may be just a matter of convention, but an instrument with the fingerboard even slightly shifted into the body may require substantial getting used to, and may be considered totally unacceptable by some players.

With the neck as light as possible it was time to start in on the body. The body blank was resawn by the steady-handed folks at Exotic Woods (http://www.exoticwoods.com), taking a 1/4" plate off the back. The resawing left the blank (including the plate) 1/4" thinner than is typical, saving a few ounces.

The back was temporarily attached to the rest of the blank using double-sided tape, and the body was sawn out, edge-sanded, rounded over, and routed for the pickup. The top was sanded and the neck was attached. The strap buttons were screwed on, the pickup taped into its pocket and the tuning machines taped to the headstock. So at this point I had a more-or-less complete instrument with a taped on back that I could test for balance. It was body heavy, as expected.

The back was popped off and the body was hollowed out from the back, leaving a solid beam down the middle to retain rigidity, and solid bosses to provide mounting points for the neck, pickup, bridge, and string anchors. This work progressed from the upper horn (where removing weight will have little effect on the balance) down to the butt end, with the back reattached for a balance check every now and then. The final lightening pattern is shown in figure 2. More wood could probably have been taken off around the horns without compromising balance, but doing so would have also structurally weakened those areas. A conservative approach was taken here.

The back plate was then glued on and the body sanded. The end result is a body cross section that, when viewed from the end, is similar to that of an I-beam, with the top and back plates being the flanges of the beam.

Figure 2 – The body was hollowed out from the back. The unhatched areas are the lightening pockets. The control cavity is at the bottom left. Bosses were left in the body for the neck joint (top), pickup (middle), and the bridge (bottom).

The body features a routed "f" hole in the top. This saves an insignificant amount of weight and it provides no noticeable change in the amplified sound of the instrument. It was included as a visual clue to the user that the body is hollowed out, and that the instrument should be treated with a little more gentleness than one might normally treat a solid body bass. Also, it looks cool.

The resulting instrument weighs in at less than 6 pounds. Balance of the instrument is excellent, both sitting on the leg and hung from a strap. Sound-wise, it compares very favorably with any modern instrument, even those with active electronics, although there are obviously less tone-shaping facilities on the instrument than are found in most instruments these days. As mentioned, this may be a minus for some players but others consider it to be a plus. That it compares so favorably in tone to a number of modern basses contradicts the conventional wisdom that heavy necks, heavy, solid, bodies, and active electronics are requirements of modern sounding instruments.

Photo 4 – The line where the back was glued to the body is seen in the foreground.

It is clearly possible to build an excellent-sounding lightweight bass using more or less conventional materials and construction. Such an instrument will not break the back of its player, nor will building one break the bank account of its maker. At less than 6 pounds as currently configured, it would be possible to add active circuitry as well as a lightweight machined aluminum bridge to this instrument and still have a bass which would be substantially light in weight.