The bridge on any guitar refers to the point where the strings meet the body. On an acoustic guitar, the bridge is a few inches below the sound hole. Electric guitar bridges are just below the pickups. The bridge affects the tone, action and intonation. When you adjust a guitar bridge, you must be aware of how any adjustment will impact the guitar's sound and playability.
How To Adjust an Acoustic Guitar Bridge
Adjust the truss rod. Typically, an acoustic guitar will not need much bridge adjustment. By adjusting the truss rod (the long screw that determines the curvature of the neck) first, you can resolve most issues with string height and eliminate any buzzing. You should consider this a necessary first step.
Remove the strings and saddle. Most modern acoustic guitars do not have an adjustable bridge. Instead, a thin piece of plastic, tusq (an artificial material) or bone needs to manually sanded down. This piece is called a saddle. The saddle can be removed easily and should never be glued on. Simply pull it off with pliers or by hand. You will need to remove the guitar strings to do this.
Sand the saddle bottom to lower height. A piece of sand paper taped to a table or workspace can be used to lower the saddle height. Keep in mind that you are removing material when you do this. You cannot reverse the process. If you take off too much, you can order a new saddle from various online merchants.
Replace the sanded saddle. You have just effectively adjusted the bridge by altering the saddle. This will normally only need to be done once if ever. A trained professional luthier can do this job for you if you are nervous about causing damage.
Replace the strings and re-tune. You will need to check the guitar after you adjust the bridge to make sure that it does not buzz.
How To Adjust an Electric Guitar Bridge
Electric guitar models vary considerably when it comes to bridge design. To adjust the electric guitar bridge you will need to consult the owner's manual for the specific brand and model guitar. Most manufacturers will have this information freely available on their websites.
Adjust the appropriate screws. Find the screws that adjust the bridge height. Some guitars have tiny knobs or dials for this purpose. You will need to adjust the bridge by tightening or loosening the screws. You should not remove the strings.
Set the intonation. You will need to tune the guitar when you are finished. You also need to check the tuning at the twelfth fret. Many electric guitars have screws to lengthen or shorten each string to the change the intonation. A digital tuner is recommended for this step.