The Bassola - Approximating the Sound of the Upright Bass

[Originally published in American Lutherie #64, Winter 2000]

R.M. Mottola

Copyright © 2000 by R.M. Mottola

Introduction

Clearly the best way to get the sound of an upright bass played pizzicato is with an upright bass. But that instrument poses a number of problems, both to bass guitarists and even to upright players- the former can’t play the instrument, and the latter often simply hate having to carry the thing around. Experiments toward approximating the sound of the upright in an instrument playable by bass guitarists constitute something of an ongoing project for me. This article describes one such effort, a large (for a guitar) acoustic instrument I call a Bassola, for no other reason than that it rhymes nicely with my last name. I hope to detail other such experiments in future articles in this series.

Functional Specifications

The project began with the accumulation of a list of functional specifications for the instrument. When engineering a new instrument (or anything that represents more than a trivial departure from some existing and well specified entity for that matter) I find it very useful to have a target to shoot at. This makes it easier to plan and deal with the design trade offs that inevitably occur, plus it provides some criteria against which to judge the finished product.

Since this was an experiment, the specifications for the instrument were divided into two sections. Books and articles offering tips on how to go about looking for a house or apartment advise generating a list of things that you must have and another of things that you’d like to have, before starting your search. The specs for this instrument were like wise divided into requirements and desirable attributes.

Requirements

As befitted the experimental nature of this project, there were really only a few hard requirements for the instrument. It had to have a “standard” bass guitar scale of 34", and use standard bass guitar strings. It had to be playable resting on the leg of a sitting player, in the manner that bass guitars are often played. And it had to fit in a car. In this particular experiment, I definitely took a “bigger is better” approach in attempting to design an instrument which approximates the sound of an upright bass, as is detailed in subsequent sections. This approach could be taken to extremes (think mando bass) but as I desired to attempt an instrument that would alleviate some of the shortcomings related to the physical size of the double bass, it only made sense to arbitrarily limit the size of the instrument. Requiring that it be able to fit into a car seemed to be a reasonable constraint.

The major requirement of course was that the sound of the instrument would be close to that of the upright bass. A sound that was a dead ringer for that of the upright would be nice, but what with the laws of physics being, well, laws, it was highly unlikely that that would happen given an instrument constrained as mentioned above. Granted this is a loose kind of requirement, one that does not lend itself particularly well to any sort of objective verification in the final product. Still it seemed reasonable for an experiment of this kind.

Desirable Attributes

Considering the likely size of the instrument, I did not make it a requirement that the thing should be playable hung from a strap, although that was a definitely desirable feature. It was desirable that the instrument had good volume, but, as even upright basses need to be amplified in most performance circumstances when played pizzicato, this was not a requirement. I was happy to trade off volume for just about any other required or desired attribute of the instrument. This led naturally to another desirable attribute, that the instrument be easily and effectively amplifiable. It was desirable that the instrument have good weight balance, an issue peculiar to basses and other large instruments, but again, as the size of the instrument was likely to be large, this was not a hard requirement. If it was simply playable that would be good enough.

A final desirable attribute was that the costs for materials of this instrument be as low as possible. After all, it was an experiment, one that could easily result in failure, and it made little sense to spend a lot of money on it for that reason.

Design

A common (probably the most common) approach to designing a new entity is to look for an existing entity which most closely meets the requirements specified, and then to modify that entity as necessary. In this case, one of the stringed musical instruments which most closely meet the requirements as specified is the 1/4 size upright bass, with a scale length generally around 36". With a deep body, high bridge, and steep neck angle, this is not an instrument to be played sitting across the leg in guitar fashion, however, so deviations from this existing design must include changes to all of these critical dimensions.

Another instrument which might be said to come close to the specifications mentioned is the mando cello. It certainly is playable sitting on the leg. With a scale length of approximately 25"¹it is shorter than spec’d, but the entire instrument could be scaled up in size to meet all of the physical requirements specified. The instrument would have to be modified to support four strings instead of eight, and would need a long tailpiece that nearly touches the bridge, in order to use standard length bass guitar strings.

The resulting instrument would be a bass guitar, but would its sound approximate that of an upright bass? It would be shorter scale, have a shorter body with substantially less body volume, and have a shorter bridge and substantially less of a break angle of the strings over the bridge. At first these differences seemed to be enough of a deviation from the physical dimensions of the upright bass to result in an instrument that couldn’t possibly approximate the upright’s sound. However, these physical characteristics would not be that much different than those of the decidedly upright sounding 1/4 size upright. I had hoped to be able to at least partially compensate for the lower break angle and the resulting diminished downforce on the top by an appropriately thinned and more lightly braced top than that of the upright.

That considered, I decided that the “large mandolin” approach might work, and proceeded drawing up plans based on a standard Gibson F series mandolin² scaled up in size to the proportion expressed by the ratio of the bass guitar scale length to that of the mandolin- 34":13.875" = 2.45:1, for a scale factor of approximately 2.5. The scale factor was rounded off a bit so that the body width at the lower bout would come out to 24", which is a typical width for the lower bout of the 3/4 size upright bass. Scaling of instruments in this manner is described in the literature^{3, 4} but what the literature describes is the scaling of the physical dimensions of an instrument as required to suit the intended tonal range of the instrument. If the mandolin were scaled up to the optimum size for an instrument in the bass range the resulting instrument would be far larger than the 3/4 size upright bass.It turns out the size of the acoustic bass is already a compromise between tone and playability (and of course portability), a fact which further reduced any qualms I might have had about attempting a bass instrument with even smaller dimensions.

Comparing the drawing of the scaled up mandolin to the “standard” electric bass guitar, the Fender Precision Bass, indicated another advantage to using the basic shape of the mandolin as the basis for the Bassola. The distance of the high waist of the enlarged mandolin to the nut of that instrument was about the same as that of the P-bass. This is an important factor in the playability of acoustic bass guitars. As the distance between the waist and the nut increases, playability in the first position decreases, except for those players with very long ape-like arms.

Although aesthetics are certainly subjective, the basic f-style mandolin shape has always had a violin family “feel” for me. Maybe it’s the body scroll, I don’t know. In any case I wanted this instrument to have as much of the look and feel of an upright as possible given the other constraints, as I suspect that the look of an instrument has at least some effect on the way it is perceived to sound by both the player and the listener. This was just one more plus of basing the shape of this instrument on that of the mandolin.

Few modifications were made to the basic profile of the mandolin in my plans, as can be seen in the completed instrument as shown “in the white” in photo 1. Some deviations from the scaled up mandolin are worth noting. The scroll was reduced in size to help reduce weight. The body depth was reduced to a rather arbitrary 3 3/8", for no reason other than that I could work the ribs and blocks with my little Ryobi spindle sander if the sides were kept to that dimension. The point of the Florentine cutaway was extended to a more horizontal (when the instrument is viewed standing upright) attitude, to help keep it balanced on the leg- remember I expected the size of the body to make this a very body-heavy instrument. The lower body “point” of the mandolin, which helps to balance that small instrument on the leg, was eliminated.

I had hoped to use bass bar and sound post bracing as in violin family instruments, in an attempt to retain some of the damping characteristics of the upright bass in the Bassola, but I chickened out and went with parallel bracing instead. Sound post placement and adjustment seems to be something of a constant battle in violin family instruments, and I was concerned that this would be even more of a problem in the Bassola, which would have considerably less down force on the top to hold the post in place. It is probably just as well that I punted on this. Local violin maker Todd Goldenberg, when he evaluated the completed instrument, mentioned that, given the shallowness of the body and the distance of the f-holes from the bridge, it would have been difficult or impossible to actually set the sound post with conventional tools for that purpose. (Note to myself: try to consult the experts before building the instrument next time!)

Construction

Construction of the instrument was straight forward and followed, more or less, standard construction techniques for a hand built mandolin.

Neck

The neck was carved from a laminated eastern hard maple blank, and features a straight tenon which mates with a straight sided mortise at the neck block. The neck extension is rabbited into the shaft of the neck, as is the practice in the manufacture of arched top guitars. The mandolin-style corner blocks are fitted to the neck and body after the neck is glued to the body.

Plates

Cost was a major issue with this experiment, and as book matched boards of a size required for this instrument are amazingly expensive, I decided to make use of cheaper alternatives for the construction of the plates. The back is made from four unmatched eastern hard maple boards glued together. Each board is approximately 1" x 6.5" x 36" long. The top is made from a single quarter sawn board of Sitka spruce cut into four pieces and glued as per the back. This board was procured from a marine lumber yard, where it is sold as mast and spar stock.

As the blanks for the plates had flat surfaces front and back, outside arching profiles for the plates were converted into topographical contour lines and transferred directly to the plates. Photo 2 shows the back so marked. The lines were cut down into steps using a hand held router resting directly on the plates. This was possible due to the large size of the plates which offer plenty of resting space for the base of the router. The resulting steps were smoothed out, first with a domed carbide carving wheel on an angle grinder, followed by a coarse rubber-backed sanding disk, also mounted on the angle grinder. Final smoothing was performed by hand. The scrolled portions of the plates were carved by hand, using gouges and planes. The insides of the plates were scooped out using the angle grinder, after first having been depth marked with drilled holes. The top was shaped to an initial uniform thickness of 5/16" while the back was shaped to a uniform 3/16". The top was parallel braced as described. Photo 3 shows the braces ready to be fitted to the top.

Ribs and Blocks

Construction here is also standard for the f-style mandolin, with bent ribs glued to a tail block and a neck block, the latter of which also implements the inside of the body scroll. A couple of issues are worth noting here. The long (scroll) side of the body is bent from a piece of maple that is approximately 54" long. this is a lot longer than standard guitar sides are usually cut, and procuring such long side material proved to be something of a problem. Fortunately Exotic Woods Co. of Sicklerville, NJ (800-443-9264, http://www.exoticwoods.com) was able to provide me with custom resawn side material for this project. The ribs were bent and clamped into an inside mold, which also served to support the ribs while the blocks were glued.

The other issue worth mentioning is the construction of the neck block. Cutting the narrow slot for the inside of the scroll in a block 3 3/8" thick and expecting the bottom of the cut to be in the same plane as the top of the cut is a dicey proposition, at least with my band saw. In order to keep the sides as straight as possible and in order to keep the amount of hand filing and sanding work inside the scroll to a minimum, I built the neck block in three layers. Each layer was cut with a router using a template pinned to the blank with a couple of dowels. The three pieces were then glued together using the same dowels to index them to each other. The pieces and the dowels are shown in photo 4, while the completed and installed neck block, featuring very straight sides, is shown in photo 5.

Other Construction Details

Again, assembly of the instrument was pretty conventional. The plates were glued to the ribs using yellow glue. The point of the Florentine cutaway was capped with a piece of maple. There are no bindings on the body, neck, or headstock. The fingerboard and nut are made of ebony, while the tailpiece was made of maple as a cost-saving measure. I had originally intended to attach the tailpiece to the body using a Saconi cello tailgut looped around a standard acoustic guitar end pin, but the end pin was not up to the task of dealing with the tension exerted by the bass strings, so a larger end pin block was fitted and screwed to the instrument using two screws, one through a standard metal strap button and the other through an electric guitar neck ferrule as shown in photo 6.

The instrument was strung up in the white, and voicing was attempted in the manner conventional with hand built arched top guitars, by scraping down the recurve area of the top and back.^{5, 6} This resulted in no noticeable change in the tone of the instrument.

In keeping with the violin family aesthetic, the instrument was varnished. After removing the fittings, the Bassola was finished with an application of a very dark hand applied stained sunburst followed by a couple of thin coats of varnish. The varnish was made from what I am pretty sure is Stradavari’s own secret recipe- one part pure tung oil, one part paint thinner, and four parts polyurethane floor varnish mixed together and applied with an old sock. Although the resulting finish doesn’t look exactly like those on old violins (I think something must have been lost in the translation of the secret recipe) it is sufficient for the purposes of this experimental instrument. The maple bridge received no finish.

Amplification

Since the instrument was intended to approximate the tone of an upright bass, I had hoped to adapt an upright transducer to it. My first choice, the great sounding and easily removable Fishman BP-100 unfortunately could not be used. This transducer uses two ceramic piezo elements which are clipped to the bridge between the strings, but as the string spacing of the Bassola was narrower than that of an upright the clips would not fit. Next, I had hoped to use a polymer piezo transducer from another manufacturer that is mounted under one of the feet of the bridge, but unfortunately I could not get that manufacturer to return my emailed requests for dimensions and specs. I ended up building both a transducer and a preamp for the Bassola myself. A single ceramic disk piezo transducer was fitted into a shallow recess under the bass side foot of the bridge, and a simple one transistor preamp was built and fitted into a shaped wooden box which mounts, piggyback style, on the tailpiece, using a Velcro band and thumbscrews through the string anchor holes so as to be easily removable. Photo 7 shows the preamp thus mounted.

Results

That the resulting instrument is visually appealing (photo 8) owes much to the classic design of the Gibson f-style mandolin from which the Bassola borrows so heavily. The dark finish, natural maple bridge, and binding-free body give the instrument much of the violin family aesthetic, which may in turn influence the expectations of those that hear the instrument.

Objective comparative tests of instruments are difficult or even impossible to realize (accent on the word objective) so I did not attempt to put together such a test. Upright and electric players that have seen and heard the instrument on its own seem to feel that the instrument does in fact have a very upright like tone. When the instrument is compared side by side with an upright bass however, it is apparent that the tone of the Bassola is less, well, bassy, and that the unamplified instrument is certainly quieter than an unamplified upright. Sustain is greater on the Bassola than on the upright when both are equipped with comparable strings. It would be interesting to see how gut or rope core strings, if such strings were available, would affect the sustain of the Bassola. When compared side by side with a flat top acoustic bass, the Bassola was easily distinguishable as having significantly more upright-like tone.

Although I consider the piezo transducer and preamp to be a work in progress, the amplified tone of the Bassola did compare amazingly well with that of a similarly transducered (transduced?) upright. The under-the-bass-side-bridge-foot location for the transducer represents a pretty good compromise between tone and feedback resistance. Tone is less tinny sounding than with transducers mounted near or under the strings, and the placement offers better feedback resistance than is generally found when transducers are mounted on the soundboard itself.

The Bassola is surprisingly well balanced when played resting on the leg. Although I was resigned to the fact that the instrument would be body-heavy and would need to be played with the body actually resting on the floor, it turns out that the scroll actually hooks nicely against the upper arm and shoulder of the picking hand, thus keeping the instrument balanced on the leg, as shown in photo 9. The instrument is quite comfortable to play in this manner. Playing standing up with the instrument strapped on is something else however. At fourteen pounds the Bassola is no lightweight and only a real he-man or Amazon-woman would consider playing the instrument like this for more than about one (short) tune.

Changes and Improvements

As built the Bassola is a more than usable instrument. However there are a few things I would definitely change if I was to continue to refine this instrument. First and foremost to be dealt with is the weight. Cutting four pounds or so from the total weight would do wonders and would make it practical to play the Bassola hung from a strap. Using mahogany for the neck, back, and ribs would go a long way towards achieving this weight reduction target. Reducing the size of the neck block would help as well.

I’m sure mandolin builders could confirm my observation that roughly half of the work that went into building this instrument involved building the scroll. Although a nice aesthetic touch, I doubt I would add a body scroll to a future experimental instrument of this type, although clearly some sort of upper bout is necessary to maintain balance of the instrument when sitting on the leg and to serve as an anchor point for the strap.

Were I to build another Bassola I would probably forgo the attempt at voicing by scraping the recurve, and would simply shape the recurve for aesthetics. I suspect that the combination of the almost round shape of the body, the shallow arching of the top, and the parallel bracing conspire to put most of the stiffness of the supported top along the braces themselves. This would explain why thinning the top everywhere but at the ends of the braces (where it is not practical to thin it anyway) had no noticeable effect on the tone of the instrument.

Given an inclination to try to improve the similarity of the tone of the Bassola with that of the upright, another attempt at an instrument of this type might try to better optimize (i.e., lower) body cavity resonance. How to simulate the body cavity resonance characteristics of an upright in an instrument with less than half the cavity volume while retaining other acoustic qualities could quite possibly keep an inquisitive and industrious person busy for a good long time.

Concluding Remarks

The big-as-you-can-get-away-with approach to approximating the sound of the upright bass as employed in the design of the Bassola represents just one of many possible ways to go about it. I am pleased with the results of this experiment, as the instrument is both quite playable and has a tone which could be well accepted in applications where upright basses are currently used. The instrument is playable by electric bass players. And it fits, barely, into any car.

References

1.  Smart, L.  “The Modern Mandolin.”
American Lutherie #56, 1998, p. 6.

2.  Siminoff, R.  Constructing a Bluegrass Mandolin
Hal Leonard Publishing, 1981

3.  Caldersmith, G.  “Toward a Classic Guitar Family.”
American Lutherie #18, 1989, p. 20.

4.  Caldersmith, G.  “The Guitar Family, Continued.”
American Lutherie #41, 1995, p. 10.

5.  Benedetto, R.  Making an Archtop Guitar
Centerstream Publishing, 1994, p. 75.

6.  Hargreaves, J.  “The Chainsaw Lutherie of Tom Ribbecke, Part Three: Assembly”
American Lutherie #58, 1999, p. 6.