The motor in each guitar is the lid and to some extent the bottom. The ribs in the lid and bottom are an important part of the "engine" that can change both the guitar's tone character and volume. The ribs are therefore important if the guitar is to sound as good as it can. There are other factors that must be right as well, among the most important being the thicknesses and stiffness of the lid and bottom. The width of the side affects the air volume inside the guitar, it and the size of the sound hole also make a difference in how the guitar sounds. The shape of the body and the bend along and across the lid and bottom are other important parameters. The list can be made long as each part of the guitar plays its role! The ribs should also make the lid and bottom strong so they do not break. The lid is especially exposed to the string pull and the rotational force of the stable.
Here I intend to describe the "ladder bracing" that I came to after many practical attempts. Each part is important for both the sound and the strength. This is what my standard rib for a parlor with a fixed stable looks like.
The lid has some unusual details, the bottom has a classic ribbed with straight ribs across. What is common to the ribs in both the lid and the bottom is that they are not completely flat on the underside but have a curvature, larger at the bottom. It is healthy for the guitar that the lid and bottom are not completely flat but are at the top in the middle, this means that the guitar can dry and shrink a bit before the lid becomes completely flat and fibers begin to pull apart with cracks as a result. A curved lid also gives a more cohesive, more stable and less "fluttery" tone.
The transverse ribs on both sides of the sound hole are standard in a "ladder bracing", you want the lid to withstand the torque from the neck and the sound hole is a real weakening. Both are important for durability and I make the top under the fretboard stronger, the same height and width but not triangulated. Neither of the two is particularly important for sound and volume as the upper part of the lid does not contribute as much as the lower one.
Virtually all the old parlor guitars I have opened up have had problems in the area when the lid was pushed in around the sound hole and the lid cracked along the edges of the fretboard. Although some had two flat sticks in spruce between the two ribs on each side of the sound hole as reinforcement. Was not happy with the solution and figured out that a couple of smaller ribs from the neck block to the lower rib should make the lid stronger. That's right, the two small sticks made the area around the sound hole extremely stable! Searched a bit online and realized that this was an old novelty, Lowden has had it since the 1990s and Martin has just started using it in some models. Called A-frame. I see no disadvantages with it. I think my refurbished parlor guitars avoid the sunken lid and cracks next to the fretboard!
The most important bar is the one above the stable. I'm trying to pick out a particularly sonorous and stiff spruce for it. Most of the sound and volume of the guitar comes from the area in the lid below the sound hole, especially the bass. When I shape the ribs, it is the stiffness of the lid's bottom that is the most important thing to keep an eye on. It must not be too stiff but not too soft. I plan on the bar and press with my thumbs and feel how stiff the lid feels. When I recognize the failure I want, I leave that bar to rest.
Perhaps the most unique detail in my rib is the barn plate in spruce. I make it in the form of a cross where the top piece is jacked out for the bottom.
The reason for the complex shape is that the stable affects the lid with a large torsional force. The stiffness in spruce is much less across the vein and the intersection allows me to combine two things in a single stable plate. The upper part ensures that the lid does not crack along the short sides of the stable on top of the lid, which is an indication where a crack is likely to begin. The lower part with the wire in the same direction as the lid is so stiff spruce can be to counteract the rotational force of the stall. In addition, you can do the lower bit as long as you think you need without the stall plate being extremely wide and large.
The fact that the stable plate is in spruce instead of maple or other hard wood is the fact that everything else in the lid other than spruce does not sound as good! Apart from the stable, I want nothing but spruce in the lid. With spruce in the stables, you get a beautiful and soft sound. The difference to the better is great.
A problem remains. The reason why a stall plate came about at all was initially to make sure that the soft spruce cover is not scratched by the string balls. Really old parlor guitars have no stable plate or a minimal bit of maple to avoid the problem of the string balls (or rather the knots on the late strings!). With mustache stables, there was no edge as a guide for lid cracks as in later rectangular pyramid stables and therefore no steal plate was needed for that reason (although I have seen cracks in the lid that begin just at the tip of the mustache stables several times, usually when attaching the round closing knob with a small nail). The barn plate turned out to be a good idea and the barn plate in maple or other hard wood grew over time as the rectangular stalls became popular. In some cases, the stable plate was transformed into a 3 cm wide knit that went across the lid. A lasting tonal disaster that basically just leaves the string sound. All old Levin parlors before the mid-1930s have one! No one thought that the sound was deteriorating! In order for my barn plate in spruce to hold for the wear, I fold round pieces into bubinga (a hard type of wood) around the string holes.
The last bar below the stable is usually not included in a classic "ladder bracing". However, I have come across old parlor guitars with a bar across the lid behind the stable even though it is mostly missing. In the same way that cracks in old parlor guitars are found at the edges of the fingerboard, there are almost always cracks in the area behind the stable. For that reason, I put in a smaller rib to keep the stable from twisting and to hold the fibers together in the lid. Nowadays I make the bar behind the stable lower than in the picture to get a little more bass, basically a flat strip.
A K&K mic gives the most natural tone I know and is easily mounted when the bottom is off. I make sure that there is enough space in front of the string holes in the stable plate.
I make all the lid ribs elliptical on the top (top in the middle) and with an even curve on the bottom. All ribs except the top and the two sticks in A-frame are triangulated. Usually about 8 mm wide at the bottom and about 11-12 mm high. The ends are given a steep slope down to about 1 mm thickness at the ends so that the entire lid can move easily. In the lid, a "stop block" is glued to the kerfing so that the bar does not come loose at the outermost tip.
The ribs in the bottom have the same shape as the lid ribs, but with a much stronger bend on the underside. I've noticed that four slightly smaller ribs are better than three powerful ones (as is often the case in old parlor guitars). You get more spruce in the bottom and spruce is always best!
You can replace the two lower ribs to the lower and wider spruce plates used in Martin guitars, among other things. I know that the bottom is softer and more flexible and that you get a little more bass from the instrument that way, while the glue surface becomes considerably larger with the plates. If you have rosewood or mahogany and a thin bottom it is a very good idea as the bottom easily breaks, the bottom of the maple and the birch are not as crack sensitive.
In general, it is good to replace all the ribs in an old guitar. Old wood becomes light and brittle over the years (various chemicals in the wood's structure evaporate!) Which is not good for the strength. In addition, the ribs are almost invariably too strong and are lying in place of standing veins. They made the ribs strong and oversized to hold, but thinner and more flexible ribs actually hold better. The lid / bottom gets the chance to move a little more without cracking. Compare with a large tree that breaks in the storm and the thin and flexible tree next to it that doesn't go off.
Old wood sounds better as the vibrations pass faster through the wood. An old lid that sounds good and newer ribs that are still tough, durable and stiff is a perfect match 🙂