Guitar bridges are the anchoring points for the strings that hold them in place under tension. But, this is not their only function, as they also transmit the string vibrations to the guitar top, help in maintaining the string spacing, and control the action on the guitar. So, acoustic guitar bridges with their constituent parts are integral components for most acoustic guitars, for their functionality and quality of sound.
The acoustic guitar bridge is made up of a saddle, bridge plate, and bridge pins. While a nylon string classical guitar doesn't have bridge pins and the strings are tied directly to the bridge. Lower levels of string tensions in classical guitar allow this. Let us discuss each of these constituents in some level of detail.
Any sound production depends on the displacement of air. Vibrating strings by themselves can displace only a very small quantity of air and produces a very faint sound. If somehow, these vibrations are transmitted onto a larger area that can displace a much larger air quantity, the acoustic instrument can produce a louder sound. This is what the acoustic bridges actually do. They transmit the energy of the freely vibrating strings to the guitar top, which has a much larger surface area.
The top is coupled to the hollow chamber of the acoustic guitar, which amplifies the sound due to resonance between the two. The bridge is placed perpendicular to the strings, which press them down to the body. The materials and construction of the acoustic bridges define their effectiveness in carrying out the intended functions and are discussed next.
Materials For The Guitar Bridge
As discussed above, acoustic guitar bridge materials should be able to transmit the majority of string vibrations without significant loss of energy. So it must be hard, not very heavy, and have sufficient strength to withstand the string tension. Some of the commonly used materials are:
Acoustic Guitar Bridge Shapes
Most acoustic guitar bridges carry shapes, popularly known as "belly bridges" because they look like a rectangle with a paunch. The paunch increases the surface area to glue the bridge and diffuses the string tension and vibrations. Gluing must be done directly to the bare wood and not over the finishes, else the joint will not last long.
On Martin and most other acoustic guitars, the belly faces the bottom of the guitar. On Gibson guitars, however, the bridge is mounted with its belly pointing towards the soundhole. They came into prominence in the 1930s, probably with the advent of steel-stringed instruments. Before them, simple rectangles were used with ornate variations like Martin's carved pyramid on each foot, Gibson's ornate mustache on its J-200, inlay work on bridge feet, and flare on the bass side to increase acoustic efficiency.
Acoustic Guitar Bridge Plate And Bridge Pins
The bridge plate is a flat brace of hardwood, usually maple or rosewood, to improve acoustic transmission and provide additional strength and stiffness to the top. Against popular belief, the bridge or the pins does not hold the strings onto the guitar, the bridge plate does.
When the strings are inserted through the hole in the bridge pins, the ball pulls up against the bridge plates, which stops them from digging up the top. Bridge pins just keep the ball jammed against the bridge plate. Firm contact and good coupling are essential for the quality of the tones. Tuning up an incorrectly anchored string can cause wear to the bridge plate and the bridge.
The size and the material of the plate have a bearing on the volume, sustain and balance of the instrument. Plywoods or other cheaper woods tend to introduce undesired elements in the tone. Maple has more resistance to splitting and exhibits neutrality towards bass or treble. Rosewood gives more musical and resonant tones on tapping.
Bridge pins aid the strings in carrying their vibrations to the top. They come in two main types - the slotted and the unslotted. The difference between the two is the groove cut into the shank of any slotted pin to accommodate the string. Slotted pins are used in conjunction with an unslotted guitar bridge while unslotted pins work with the slotted bridges.
Unslotted pins are more common. They have no groove. Instead, the guitar bridge has a notch cut in front of the pinhole to accommodate the string. The pin presses against the string and prevents it from slipping out. The selection of correct pin material can make a difference in getting the desired tones.
Bridge Pin Materials
Acoustic Guitar Bridge Plate Arrangement.
As stated above, guitar bridge plates are pieces of stiff hardwood that adds some strength to the area. The plate wood along with the top bracing of the instrument plays an important part in tuning the acoustic guitar to its natural tones. The X - brace design on the acoustic guitar allows the luthiers to accommodate the bridge pin holes and plates, which is not possible with the fan bracings.
So, the classical guitar's bridge has small holes drilled through a raised section in the back of the saddle, through which the strings are looped. The arrangement is known as a loop bridge and it is the bridge that bears all the string tension rather than the plate.
Acoustic Guitar Saddle
Saddles are strips of dense materials like bone, placed in the groove of the guitar bridge, known as the saddle slot. The strings sit on the saddle before passing through the pin holes. A correctly set saddle is absolutely essential for the best intonation. Intonation, as you may be aware, is a measure of the tuning of an instrument along the entire length of the fretboard.
Grinding down, shimming up, or replacing the saddles with shorter or taller ones will help you to set the height of the action. Strings with higher action require more pressure to fret the notes. The animal bone saddle is almost a standard in most high-end instruments. It increases the loudness and dynamics of the guitar.
The saddle top has to be smoothly curved to prevent string breakages. Flat Top acoustic guitar and classical guitar saddles are usually without any grooves cut in them unlike the archtop, electric, and twelve-string guitars. The only exception can be when the bridge pins are not perfectly positioned in the guitar.
Why Use A Compensated Saddle
Perfect positioning of the saddle and hence the acoustic guitar bridge is essential for your guitar playing in tune. The twelfth fret should be in the exact center between the saddle and the nut. Different string compositions and gauges result in different vibrating lengths, necessitating different adjustments for each string. The phenomenon is more pronounced between the wound and unwound strings and needs to be compensated.
To compensate, manufacturers adjust the shape and angle of the saddle on the bridge. The saddle slot is cut at an angle in most modern guitars, making the low string end farther away from the neck than the higher ones. Even better compensation is achieved by having separate offsets for the two high and four low strings. A separate saddle slot is needed for each offset.
Another way to compensate is by providing grooves on top of the saddle. This lowers the height and the break angle of the strings. The grooves are provided on the high-end strings.
Many players modify their acoustic guitar bridge saddles by adjusting the heights and grooves to fine-tune their instruments.