This area of the guitar has to accept a huge amount of stress from the strings. According to the D’Addario strings web site, a set of light gauge phosphor bronze strings exerts 178.3 lbs. of pressure on the bridge of an acoustic guitar; mediums exert 192.3 lbs. (As a side note, the site also states that a set medium gauge strings for an acoustic 12-string pulls 322 lbs.! This is the reason a 12-string should NEVER be tuned up to natural pitch. More on that in a future column.) And in most cases the only thing that is keeping the bridge from flying off is some glue!
That white piece of plastic, bone or some synthetic material embedded in the bridge is called the saddle. This is a very important part of any guitar for many reasons. First and foremost, it is at one end of the “business” part of the string, i.e., the part that vibrates. The saddle must be located with the utmost precision to ensure perfect intonation when strings are fretted. Back in the 1970s some Martins came out of the factory with bridges (and therefore saddles) glued in the wrong locations. The result was some otherwise fine guitars that were totally out of tune up the neck. This can be remedied by a qualified guitar tech and Martin did their best to make good on their famous lifetime warranty with these faulty guitars but if a bridge has been in place for a long time a correctly placed bridge results in a lighter line of wood on one side of the bridge or the other. Not a desirable thing with a guitar that should be worth well into the four-figure range!
Not only must a saddle be placed in the correct position, it must also have the correct amount of curvature on the top so the strings cross it in a way that won’t cause buzzing or muffle the vibration. “Compensated” saddles are standard on many guitars. They feature a slightly different section slightly back from the rest of the saddle for the G string to cross. This is because core of the wound G string is a much thinner diameter than the other strings and because of this, during the act of pressing down that string is bent more than the others. If the saddle is straight across, and depending upon the amount of force that is used to press down that string, it can sound sharp compared to the other strings.
The height of the saddle is another important aspect. The higher the saddle, to a point anyway, the more severe the “break angle, ” which the angle between where the string emerges from the bridge and the top of the saddle. A sharp break angle results in more tension on the string, which in turn makes the string press harder on the bridge – a good thing, sound-wise. A very soft or slight break angle and the strings will often sound dead and lifeless because more of the string makes contact with the top of the saddle, and the string may actually be able to move BEHIND the saddle, resulting in a dull sound and buzzing. Some people lower the action on their guitars by filing or sanding the saddle. If you choose to do this, always sand the BOTTOM of the saddle (which should easily slip out of its groove – never glue in a saddle). But be sure to do a tiny bit at a time and check the height frequently.
Bridge and saddle materials very much affect the sound of any guitar. The harder the materials used, the better the vibration is transmitted and the better the sound. Bridges are usually made of rosewood, ebony (on expensive guitars) or synthetics. Saddles are made of hard plastics, bone or even fossilized walrus ivory. In the old days, elephant ivory was used but this is now illegal. I firmly believe that bone saddles and nuts improve the sound of almost any guitar due to their hardness compared to plastic. The fossilized walrus ivory (completely legal) is nice but obscenely expensive.
The huge amount of pressure on the bridge sometimes causes lifting, cracking or even total detachment. A good guitar tech can re-glue and clamp a bridge; this is not a job you should attempt because special glues and clamps are used. A cracked bridge should be replaced. Never use epoxy to glue a bridge – or anywhere on your guitar for that matter.
I may be making this all sound like bridge problems are inevitable. This is certainly not the case; I’ve seen Martins and Gibsons that are going on 100 years old with original bridges in perfect condition. Also know that the area of the top where the bridge is glued is heavily reinforced inside with braces and an extra flat piece of wood glued to the under side of the top, called a bridge plate. So don’t worry, but keep an eye on your bridge!
Peace & good music,