Fitting necks and bridges on a double bass

Many violin makers prefer not to work with double basses. Often they don't have the space, or the right tools. They might not feel confident about working with such a big instrument, they might not particularly like double basses, or know much about them. Perhaps some, remembering all those jokes in violin making school about double bass work and carpentry, might even feel themselves a bit of a failure were they to let a double bass come into their ateljé. Such hit and miss woodwork hardly demands the kind of precision or deep knowledge of the art form that violin making does. Or does it?

A typical task for a violin making practical exam is to fit a neck on a violin using a dove tail joint. This is not easy as one is working in three dimensions and there is only a single point, lying at the intersection of four different planes, that is correct. Inching your way along here is not the right word, more like millimetering your way, no micrometering woodshaving by woodshaving towards this correct point, all the time making the four important checks. Firstly, when you look down on the instrument from the top, the line that runs through the ears of the scroll needs to run parallel with the line that you can see between the ribs and the table. Then, looking down over the fingerboard you  need to make sure that it lies exactly down the middle, which you do by comparing distances from the f-holes. In fact for this check, you need to really look at the instrument from all angles, even from the back. Next, the angle of elevation. The angle of the foot should be 87 degrees and this should mean that at the foot of the neck, the fingerboard lies 6mm on each side above the purfling on the table and the end of the fingerboard should lie 21 mm above the table. This should correspond to a standard bridge height of 33mm. Finally the neck should be sufficiently sunk into the joint so that the distance along the fingerboard between the edge of the table and the top saddle, or nut, is 13mm long. Phew, what could be harder than that?

Fitting a double bass neck, of course. Here there are no standard measurements, so you have to first work out which measurements you are going to need, in relation to the body form. Important things that need consideration here include the symmetry of the instrument, especially around the f holes; the depth of the ribs and how round the upper bout is (a very round form will need a neck set further away from the body for the instument to be playable in the higher positions, but only if the ribs are not to deep); the thickness of the table, how flexible and how strong it is (if the table is thin and weak the neck angle should be less steep in order to reduce the pressure on it from the strings) and finally the proportions of the body length to the neck length. If this is wrong the instrument will be unplayable. The crook in the neck needs to be exactly opposite D on the G string, or sometimes Eb depending on the preference of the player. This is not something you need to worry about so much on a violin, but is very important on a bass. The other important difference of course is that the pressure from the strings on a bass is absolutely enormous which makes a perfect fitting at the neck joint all the more crucial.

So now we have dealt with some of the issues of neck fittings I´ll move on to a little case study on a bass bridge I did a little while ago that demonstrates the relation between setting of the neck and the carving of the bridge. One could think of the bridge as being in a way an extension of the neck/fingerboard. The instrument in question came in in two pieces, neck and body, and the instructions "this bass was about to go on the rubbish tip, see if you can do something with it, maybe you can use it for spare parts." I said I don't know about spare parts but if it can't be resurrected I'll use the table for a sign post and the back and ribs I will fit with shelves and hang on the wall. So much for my fun ideas, on closer inspection I realised that it would be quite possible to glue the open seams, refit the neck and set it up to a perfectly respectable student bass. So that is what I did.

Now let me show you the outlines of the old bridge and the new bridge and explain the differences.

Here is the original bridge. If you look along the bottom, you can see that the table was misformed, being higher on the treble side than on the bass side. The right (bass) foot is lower than the left, if you compare to the rather faint line that shows the level. This is pretty common, and can be exacerbated by having a sound post that is fitted too tightly, pushing up that side of the instrument. When this does happen, it is important to take this into consideration and compensate by making that leg of the bridge longer. On this bridge they haven't thought of that and the two legs are the same length, both 65mm. The result being that the whole top of the bridge is shifted to one side. Compare the solid line with the perpendicular dotted line. This results in the strings not being centered over the fingerboard, but shifted over to the bass side, making it impossible to play. So when that happens the simplest solution, as they did in this case, is to move the bottom of the bridge over to the treble side and then the strings lie in the right place. This is not ideal because now the pressure on the area between the f-holes is uneven, and the vibrations may not be properly activating the bass bar (which lies underneath the bass foot).

But there is another problem here and that is the relative height of the bridge on the bass side compared to the treble, 64mm compared with 53mm. The bass strings need to be a bit higher because they are thicker and vibrate more widely and may buzz against the fingerboard if they are too low. But if they are too high in relation to the treble strings then a player may have to work harder to get their arm around the instrument to bow on the top string. It is better if the top of the bridge has a flatter profile. The best way of countering this problem is by resetting the neck (obviously not always possible, sometimes a wedge under the fingerboard will do) so that the length of the fingerboard is tilted slightly over to the bass side.

The bridge height of 173mm was also quite high considering that the neck and the bottom saddle were originally set quite low to the instrument, suggesting high tension by the strings on the bridge. As a general rule of thumb, I like my bridges to be more or less as high as they are wide. So when I reset the neck, as well as angling it slightly, I also added a new piece of wood to the end of the neck foot so that the fingerboard didn't lie so close to the table. Then I set it at less of an angle so the height of the bridge wasn't as high.

So here is the final result. The table is still deformed (correcting that would entail a full plaster cast mould and reshaping, the cost of which would exceed the value of the instrument) but that doesn't matter anymore because I have adjusted the respective lengths of the feet so that the bridge stands properly upright, the centre line is perpendicular. The upper measurements are now 49mm to 46mm which is as it should be. The height now a perfectly respectable 160mm with the heart nicely centered in the middle. And the firewood that was destined for the container is now being played by a deserving student.
So, when you need to have your bass set up, and your local violin repair person will not accept it, don't take it to the nearest carpenter, or let your uncle or friend loose on it.... Ok, real bass repairers are not easy to find, so you can give it to your uncle or friend if you really want to..... but, first make sure they read and understand this and then see if they are they are still up to the challenge.