Bracing the Soundboard

Arguably one of the most important things for the tone of a guitar is the bracing layout. It is a very rigorous process that takes some time to complete but really makes a difference in the tone of the guitar. Bracing a guitar refers to a system of wooden struts that support and reinforce the soundboard and the back. We do this in order to strengthen and stiffen the soundboard, while keeping it as light as possible.

The first thing to do was to thin down the top of the guitar. Since I am using a hardwood as my soundboard, I needed to thin it down a little more than I would if I were using Spruce. The top for the parlor guitar is approximately 2 mm. To do this, the piece was just sent through the drum sander for multiple passes until the desired thickness was reached. Next, it was time to mark out the top bracing pattern. This is a traditional parlor bracing pattern. You can see how the braces are drawn on with pencil. When you look inside the sound box of a guitar, it is very common to see stray pencil marks, especially on the soundboard.

The next step is to start preparing the X-brace. The X-brace is the largest brace and bears most of the 150-lb tension that are applied to the top by the strings. The braces will all be made out of Spruce. The wood must be quartersawn with little run out of the grain. The picture to the left shows the X-brace, which has been created by two separate braces that have been notched out to form a 90 degree angle.

Once these braces are built, the they fit together and are completely flat, it is time to glue them to the top. Some guitars have a very large radius to the top. Typically this is roughly a 25-foot radius and it helps to focus sound. Additionally, the slight arch in the top can help to prevent caving and bellying of the soundboard under the great deal of tension from the strings. Due to the size of the parlor guitar, a radius is not necessary. Therefore, the X-brace is glued in on a flat surface. You can see in the picture to the right, the braces are glued down using fiber glass rods on a shop built go-deck, which gives equal pressure across the entire brace.

After letting the glue set up and stay in the deck for about an hour, we are able to take the soundboard out and leave it be for a few hours so. The form is then cut so that there is just a small amount of excess wood that over hangs the actual top of the guitar. This will be taken off when we glue the sides on.

Next it is important to take some of the stock off the spruce so that it allows the top to vibrate. To do this we take a chisel to the ends to form a scallop. This reduction in the ends of the braces allows for there to be more vibration towards the rim of the guitar. Additionally, it is believed that this helps to bring about more low end response. There is a lot of argument between scalloped and non-scalloped braces. Luthiers have their own styles and own beliefs. I personally have played many guitars with and without scalloped braces and they all have their place. For this guitar, I chose to stick with the plans that are outlined by LMI.

Next, I took down the edges of the braces using the same chisel so that they begin to look more like a triangle. Again, this is just taking away some of the rigidity of the braces which allows for more vibration of the top, this giving more sound. By shaping the braces, a luthier can tune the top so that it has optimal tone.

Finally, the last bit for the day was to glue in one of the cross-braces. This brace was shaped slightly prior to glue up. however, much more shaping will be completed, and there are many more braces to be added.

This last picture just shows some additional detail of the X-braces that have been slimmed down. There will be additional amounts of work completed on these braces, but this is just to get a start on all the work inside the box that needs to be done.