Setup:: Bridge AdjustmentBridge adjustment is one of the more critical issues for set up on the bass. Without this critical process, your instrument will be out of tune as you move up the finger board, unless you are playing a fretless bass. Before attempting bridge adjustment, you should determine if your neck needs adjustment first. This is because if you adjust your neck after setting up the bridge and strings, you will likely need to do them all over again. If your neck is straight on both the high side (G string side) and low side (E string), and there are no problems like excessive string buzzing, then proceed with adjustment of the bridge. The first priority consideration now is the height of the strings above the finger board. The strings should be as low as possible for your playing styles, so that the strings do not buzz, unless that is part of the sound that you are looking for, and sometimes it is called for with certain pieces of music. But generally, you will want or need a clean sound. The second consideration is whether the strings are the correct height above the pickups. If the strings are too close to the pickups, the magnets in the pickups will dampen the string vibrations and cause odd harmonics to develop when playing the bass. If the strings are too far from the pickups, the signal will be weak and there will be less midrange and high frequency information going into the pickup. Thus, there is an optimum distance, and it varies for each pickup design. Typically, you want your strings about 3/16 inch (4mm) to no more than 7/16 inch (11mm) from the pickup. Again, this will vary from one instrument to another. These are merely basic guidelines for the novice. But remember, pickups can and should be adjusted after getting the strings heights set correctly.
The other consideration here in bridge adjustment, is matching the radius of the finger board. All bass finger boards have a slight curve, which the bridge needs to match. Typically, most bass necks have a radius between 7 and 10 inches for this curve. By matching this adjustment at the bridge, the strings have a more or less uniform distance above the finger board. Below is a photo providing some good detail information about bridges.
When adjusting the bridge, I would recommend setting the string heights by adjusting the saddle adjustment screws. Remember to match the radius of the neck when setting the string heights. Be sure to have the strings tuned and be using the string set of your preference, when doing these adjustments. You may need to raise the lower strings higher than the others when doing this setup. After adjusting a particular string, play the string as you normally would, playing all of the notes on the finger board, and see if it sounds good, and does not buzz against the frets. If the action feels comfortable and playable, then move on to the next string and repeat this process. Once all of your strings are set at the best height, then you need to adjust the string length for correct intonation. If this is not done, your bass will be out of tune as you move up the finger board. First tune the instrument. Now lets test the G string. Start by playing the harmonic on the 12th fret of the G string (this is done by lightly pressing on the string exactly above the fret, but do not press the string against the fret board.) Then play the same note, only normally pressing against the fret board. These two notes should be exactly the same. If the normally pressed note is lower than the harmonically played note, the string length is too long and needs to be shorted. If the normally pressed note is higher sounding than the harmonically played note, the string length is too short and needs to be lengthened. Adjust the string length screw at the bridge, and repeat the test until the harmonic matches the normally played note. Then repeat this process for the other strings. Now that you have your string lengths adjusted for the 12th note harmonic, do the same test and adjustment for the 19th fret harmonic. You may need to compromise your adjustment between the 12th fret harmonic and the 19th. If you have a severe problem, you may have your string height set too high for the bass. A lower string height will have less tension variance between these notes, and will be easier to set up. You may have to experiment with different strings. And remember, that when you change your strings, especially to a different gauge or manufacturer or type, you will need to repeat many, if not all of the set up procedures listed here.
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