What does the inside of your guitar look like?
Feb 27, 2017 12:42:13 GMT -5
CTGull and ancient1 like this
Post by freemankeller on Feb 27, 2017 12:42:13 GMT -5
When a bunch of guitar geeks get together one of the default topics of conversation is guitar bracing. I've built a bunch of guitars with different bracing and thought it would be interesting to post some pictures and see what kind of discussion develops.
A couple of caveats. First, remember that there are infinite variations to each one of these patterns - you can move a brace (shift it forward or back or open it or whatever...) and it will change the way it works.
Second, remember that a brace has three main functions. First, it strengthens the top wood against splitting with the grain (meaning that it has to run somewhat across the grain). Second, it needs to strengthen the weak areas of the soundboard while letting other parts move and vibrate. Third, it has to be able to color and "voice" the sound.
Third, remember that a brace is just an engineered beam. The properties of a beam is that if you make it wider the strength and stiffness (which are different) go up in proportion to the change. If you increase (or decrease) the height the stiffness/strength changes with the cube of the change. In other words, make it twice as wide and its twice as strong, make it twice as tall and its 8 times as strong. A little scalloping makes a big difference.
Fouth, while bracing patterns can be very different there are two areas of weakness that have significant braces. The area under the bridge almost always has some sort of bridge "plate" or "patch" - it couples the bridge to the rest of the top and provides a strong hard material for the string balls to rest against. The other very weak area in every guitar is under the fretboard extension near the sound hole - the tension on the neck is trying to pull the extension right thru the top so most guitars have a great big "upper transverse brace". Othewise you would see little cracks in the top from the f/b to the sound hole.
Last for the theory stuff - remember the two different ways that guitar tops work. On an instrument with a pinned bridge or tieblock the ends of the strings are anchored right behind the bridge and the tension wants to rotate the bridge around its cross axis. In other words it wants to pull the lower bout up and drive the area between the bridge and sound hole down. When you pluck the string it causes the top to rock as well as vibrate in other modes.
A guitar with a tailpiece (archtop, mandolin, violin, resonator, SelMac......) doesn't have that rotational component - most of the string tension is anchored at the tailpiece but a component goes vertically into the top. When you pluck the string there is very little rocking of the top, its mostly straight up and down.
Still with me?
Here is about the simplest of all bracing patterns, the basic "ladder braced" guitar. It has great cross grain strength and can hold the top dome pretty well. You can see the maple bridge plate and the big UTB above the soundhole. There is very little bracing against that rotation torque which is a problem if this was a pinned bridge. However this particular guitar will have a tailpiece so it actually works pretty well. Ladder braced guitars tend to have a lot of fundimental and not a very complex sound (think old Depression era guitars and SelMacs).
Next is the classic classical or so called "fan bracing". Classicals have about 1/2 the tension of a steel string, you can see two UTB's, the bridge patch and the fact that the braces are angled more or less across the grain. Lots of variations on this theme
The modern X brace is an engineering masterpiece. It is credited to CF Martin I but others were screwing around with the idea in the mid 1800's. Anyway, here is a typical example. The X has its greatest strength where it crosses between the bridge and soundhole, the weakest part of the top. The wings of the bridge sit over the arms of the X and impart their vibrations into the braces which then drives the top. The bridge plate is nestled into the X and you can see two "tone bars" between the legs - the are there to color the sound ("braces" are mainly for strength, "bars" are mainly for tone). A big UTB and a small flat "popsicle" brace at the upper bout. The braces are fairly wide (5/16) but I scalloped the heck out of the and this guitar is remarkably responsive.
A different top (happens to be mahogany) with deeply scalloped braces. The top was pretty stiff so I took a lot of wood off of the braces to get them to move.
Here is another X braced guitar but the braces are not scalloped (instead they are thinned near the top). Small guitar, single tone bar
Archtop guitars, mandolins, violins frequently just have a couple of tone bars to help voice the top
Archtops may have simple X braces for that cross grain support. They may or may not have a bridge patch and/or UTB. Without a central soundhole the top moves in completely different fashion from a normal acoustic
A couple of caveats. First, remember that there are infinite variations to each one of these patterns - you can move a brace (shift it forward or back or open it or whatever...) and it will change the way it works.
Second, remember that a brace has three main functions. First, it strengthens the top wood against splitting with the grain (meaning that it has to run somewhat across the grain). Second, it needs to strengthen the weak areas of the soundboard while letting other parts move and vibrate. Third, it has to be able to color and "voice" the sound.
Third, remember that a brace is just an engineered beam. The properties of a beam is that if you make it wider the strength and stiffness (which are different) go up in proportion to the change. If you increase (or decrease) the height the stiffness/strength changes with the cube of the change. In other words, make it twice as wide and its twice as strong, make it twice as tall and its 8 times as strong. A little scalloping makes a big difference.
Fouth, while bracing patterns can be very different there are two areas of weakness that have significant braces. The area under the bridge almost always has some sort of bridge "plate" or "patch" - it couples the bridge to the rest of the top and provides a strong hard material for the string balls to rest against. The other very weak area in every guitar is under the fretboard extension near the sound hole - the tension on the neck is trying to pull the extension right thru the top so most guitars have a great big "upper transverse brace". Othewise you would see little cracks in the top from the f/b to the sound hole.
Last for the theory stuff - remember the two different ways that guitar tops work. On an instrument with a pinned bridge or tieblock the ends of the strings are anchored right behind the bridge and the tension wants to rotate the bridge around its cross axis. In other words it wants to pull the lower bout up and drive the area between the bridge and sound hole down. When you pluck the string it causes the top to rock as well as vibrate in other modes.
A guitar with a tailpiece (archtop, mandolin, violin, resonator, SelMac......) doesn't have that rotational component - most of the string tension is anchored at the tailpiece but a component goes vertically into the top. When you pluck the string there is very little rocking of the top, its mostly straight up and down.
Still with me?
Here is about the simplest of all bracing patterns, the basic "ladder braced" guitar. It has great cross grain strength and can hold the top dome pretty well. You can see the maple bridge plate and the big UTB above the soundhole. There is very little bracing against that rotation torque which is a problem if this was a pinned bridge. However this particular guitar will have a tailpiece so it actually works pretty well. Ladder braced guitars tend to have a lot of fundimental and not a very complex sound (think old Depression era guitars and SelMacs).
Next is the classic classical or so called "fan bracing". Classicals have about 1/2 the tension of a steel string, you can see two UTB's, the bridge patch and the fact that the braces are angled more or less across the grain. Lots of variations on this theme
The modern X brace is an engineering masterpiece. It is credited to CF Martin I but others were screwing around with the idea in the mid 1800's. Anyway, here is a typical example. The X has its greatest strength where it crosses between the bridge and soundhole, the weakest part of the top. The wings of the bridge sit over the arms of the X and impart their vibrations into the braces which then drives the top. The bridge plate is nestled into the X and you can see two "tone bars" between the legs - the are there to color the sound ("braces" are mainly for strength, "bars" are mainly for tone). A big UTB and a small flat "popsicle" brace at the upper bout. The braces are fairly wide (5/16) but I scalloped the heck out of the and this guitar is remarkably responsive.
A different top (happens to be mahogany) with deeply scalloped braces. The top was pretty stiff so I took a lot of wood off of the braces to get them to move.
Here is another X braced guitar but the braces are not scalloped (instead they are thinned near the top). Small guitar, single tone bar
Archtop guitars, mandolins, violins frequently just have a couple of tone bars to help voice the top
Archtops may have simple X braces for that cross grain support. They may or may not have a bridge patch and/or UTB. Without a central soundhole the top moves in completely different fashion from a normal acoustic
