Issue 4

Getting Your Bass Playing The Way You Want

Part III

The Bridge and Nut

The bridge and nut serve two functions: holding the strings in proper position for playing the bass, and transferring the tonal vibrations of the strings to the instrument’s sound chamber. Both bridge and nut can have a profound effect on a bass’ playability, depending on the height at which they hold each string, and the spacing between the strings. They also play an important role in keeping the strings centered over the fingerboard.

The Nut: Generally made of ebony, with the grain at 90 degrees to the grain of the fingerboard, the nut is the piece located at the upper end of the fingerboard, which is grooved to guide the strings into the pegbox. Providing the fingerboard has been properly dressed, a bass plays and sounds best when the nut grooves are cut quite low. I like to be able to just slide a business card under each string where it meets the nut; the card should encounter a bit of resistance. When the nut grooves are too high, a bass will lose sustain and liveliness of tone, and be difficult to finger in the lower positions. When cut too low, a buzz or rattle will occur when the open string is played. A word of caution here: It is common to encounter a bass fingerboard that has been slightly rolled off downward at the nut, as a result of incorrect planing and/or polishing technique. This needs to be checked for with a small straightedge before lowering the nut grooves, otherwise a nasty buzz will be the likely result. Of course the fingerboard dressing ought to be properly re-done, but this is not always an immediate option.

The spacing of the strings at the nut is commonly between 9 and 11 mm, measured from string center-to-center. I prefer 10mm, and I like to have about the same amount of fingerboard revealed to the edge of both the E and G strings.

The nut grooves should be just slightly wider than the string, and cut about ½ the string’s diameter down into the nut wood. The grooves should be cut with a slight downward angle (toward the pegbox) where the groove meets the fingerboard. From there, each string groove should gently slope downward toward its tuner shaft. The grooves need to be lubricated with graphite, ideally from a soft pencil.

I have heard both classical and jazz players express serious surprise at the amount of playability improvement that a simple nut adjustment can provide. Improvement in tone is an occasional bonus.

The Bridge: Made of quarter-sawn maple, the bass bridge holds the strings at the proper height from the body, and is arched to allow for effective bowing. Several important decisions must be made before selecting or making a bridge blank to be used on a specific bass: 1) How wide a bridge does this bass need? 2) Do I want adjusters, and if so, what type? 3) Do I wish to alter the string length? 4) Do I wish to alter the tone, and if so, in what way?

The width of the bridge blank to be used is determined mainly by two factors; the distance between the upper eyes of the f-holes, and the position of the bass bar under the bridge when the bridge is centered on the top table. It is considered desirable to use a bridge not much wider than the distance between the upper eyes of the f-holes. The reason is that a wider bridge exerts pressure outside the area of the top table which contains long grains of wood to transfer the pressure. As a result, the top may sag around the f-holes from a bridge that is too wide. The bridge should sit with its E-side leg partially over the bass bar. The position of the bass bar needs to be mapped out on the top table with a grease pencil in the area of the bridge, and a blank chosen which sits nicely over the bass bar. Sometimes a bridge must be chosen which is slightly wider than the distance between the upper eyes of the f-holes, due to the position of the bass bar. And sometimes a bridge must be chosen that is considerably narrower. In general, a wider bridge promotes a deeper sound, and a narrower one, a more focused sound. However, the position of the bridge over the bass bar is most important; a bridge that is too wide can actually sound less deep than a narrower one, if the bridge leg sits farther out than the bass bar.

Bridge adjusters are pretty much a necessity if the bass lives in a temperate environment. Adjusters allow the player to adapt his bass to dryer and wetter climatic conditions, the condition of the player's chops, and also allow small bridge crown adjustments without bridge replacement. There are many opinions as to which type of adjuster is best; there are aluminum, maple, ebony, carbon fiber, polymer and titanium (and possibly others) to choose from these days. Each has its advocates, yet the difference in tone and response between them is minor. I believe that a good material for bridge adjusters combines fairly high density with light weight, and for that reason I usually use aluminum. It makes sense to me that the adjuster should be as close to retracted as possible, with just enough play to allow for seasonal repositioning. When the threaded adjuster shafts are quite exposed, there is less thread inside the bridge making tonal and mechanical contact, and I think the tone suffers (stripping-out is also a danger). I don't think there is a tonal difference between bridges with the adjusters installed threads-up and those installed threads-down, though I prefer the latter (it just looks better to my eye). There is still controversy over which sounds "better"; a solid bridge, or one with adjusters. I have cut many hundreds of bass bridges, and I prefer the sound of a bridge with adjusters. I think the added flexibility allows the feet to nestle more closely into the top table, and I nearly always feel that I hear an improvement in clarity when I install adjusters in a solid bridge. I'm sure I'll get letters about that one.

A slight amount of string-length adjustment can be achieved by the positioning the bridge and by adjusting the angle at which the feet are cut. And a slight bit of tonal adjustment can be achieved by choosing a bridge with wider-grained, softer wood, vs. narrower-grained, harder wood. In general, the harder wood will provide a slightly brighter sound.

The two most important things a bass player can do to keep his bass playing and sounding its best are to keep the bridge properly positioned, and keep it free of rosin and dirt. Know your string length, and the proper position of your bridge as it was fit by the luthier, and check it regularly. And keep the junk off it, as an undulating bass bridge transfers its energy best without added mass.

Please send your questions to: ArnoldS@aesbass.com.


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