If this page has a tendency to be patchy and even repeat itself, it is because I use it as
a sort of notebook to keep track of ideas that are influencing my work.

Hopefully, reading it will help people to understand the instruments that I make
and why they sound and feel different from guitars as they know them.

Engineering, electronics and most modern design disciplines are driven by the need to be constantly better than what went before. Acoustic musical instruments on the other hand don't seem to have much evolutionary force driving their development. Most musicians want to play copies of the instruments that their heroes in the past played. With so many factory made copies around, many musicians never get an opportunity to find out what a really good instrument sounds like.

The vast majority of luthiers are traditionalists, which means they assume that people in the past have solved most of the problems of instrument design and are happy to follow in their footsteps. Some others are compelled to look at everything from the ground up, so that they understand the whole process and can manipulate it. Due to a general distrust of human knowledge, I belong to the latter category.

Once when I was arriving to do the sound mixing at a concert. I heard a classical guitar as I approached the hall and I thought they must have set up the sound system without me. When I entered the hall I saw two guitarists practicing a duet with no amplification. One of the guitars (a Greg Smallman type with graphite lattice bracing) was filling the hall with sound. The other expensive but traditional guitar was barely audible. This experience among others, has convinced me that Greg's approach to guitar making is probably the most important development in acoustic instrument design for a long time.

Having said that, I will point out that I have never tried to copy Greg Smallman's guitars. Rather I have found that every Greg Smallman and Peter Biffin concept that I have encountered has been relevant to my own exploration of acoustics.

The ideas below are ones that have helped me to best understand how musical
instruments function and to get the sounds that I want from them.
Other luthiers will have different approaches that work for them.

I define the soundboard not as the top of the guitar, but as a specific area of top around the bridge that has the function of converting the bridge energy into sound. (think of a speaker cone) In most classical guitars this area finishes at the brace below the soundhole, whereas in most steel string guitars it continues up to the big brace where the fingerboard ends. The size of the sound board and how it functions is determined by the braces. In my guitars the three functions of the braces are to strengthen the guitar, to isolate the moving sound board from the rest of top, and to transfer vibration from the bridge to the whole soundboard.

In some designs like the X brace pictured below, the braces are more an extension of the sound board than of the bridge. This is a less efficient system as it requires a heavier top to transfer the energy.

Many people visualize the guitar strings pushing up and down on the top of the guitar. But the main energy of the strings is produced by them changing length as they vibrate. That means that the string energy is moving at right angles to the direction you want the soundboard to move. A guitar with a tailpiece like a mandolin easily converts the energy by pushing the bridge straight down as the string shortens. Because the downwards pressure is continuous, it damps the sustain and low frequencies as the angle gets steeper. This gives tailpiece guitars a distinctive percussive sound much loved by jazz players.

On the other hand, guitars with a fixed bridge and no tailpiece have to convert the twisting motion of the bridge as it is pulled and released into up and down movement in the sound board. The most obvious problem is that as the front of the bridge moves down, the back of the bridge moves up. If different parts of the sound board move in opposite directions then certain frequencies will disappear. This effect is called 'phase cancellation'. Quite a large percentage of the energy produced by the strings is lost by different parts of the instrument moving out of phase with other parts.

My approach to phase problems

My approach is to 'lock the bridge' by having strong braces running right under the bridge stopping it from rocking. (shown below) Having done this, I then have to create a place where that locked in energy can be used to produce sound. I stop the braces short of the sides to allow the whole bracing structure to move. I use tight braces on the upper zone between the bridge and the sound hole and looser bracing below the bridge. This causes a hinge-like action to top move as a whole allowing even a small guitar to produce clean bass frequencies. The light, hard carbon braces give it a distinct high treble and produce sustain all the way up the neck.

This way of harnessing the rocking motion of the bridge creates a sound more like an arch top instrument (guitar, mandolin, violin), increasing the dynamic range. This is ideal for melodic and jazz players, especially those who don't want to use heavy strings to get the guitar to perform. I would like to point out that if you want a strum and sing type of instrument you are probably better off with a standard X brace type guitar.

Martin X bracing was first used in the mid 1800s on nylon strung guitars, but it wasn't until the higher tension steel string guitars came along that it became really viable. The large X in the middle does two very clever things. Firstly it defines a small loose zone around the bridge creating an area to produce high frequencies. Secondly the X itself is set in motion and becomes a bass speaker moving like a hinge.

When it works correctly, this "double soundboard" creates a good balance of treble and bass, making it so successful that probably over 99% of flat top steel string guitars use this type of bracing.

There are some frequencies lost by the rocking motion of the bridge creating phase cancellation. These lost frequencies (mostly around the G string) create a dead spot in the middle of the instruments range. For rhythm playing this missing midrange is sometimes an asset, especially in styles where you hit a bass note and then play the rest of the chord on the offbeat, as it separates the two sounds.

This bracing design doesn't work well without a solid soundboard, so it needs heavy strings to work properly. It is not a very efficient system.

A more efficient instrument

Below is a picture of one of my designs. If the central X which passes under the bridge saddle is made rigid, then the bridge will not rock, but the energy will be sent through the whole brace structure. This will produce a sound much like a tailpiece guitar, working as a single soundboard with the treble coming from the tight braced areas and the bass coming from the loose soundboard edge. The midrange remains strong because there is no phase cancellation causing it to drop out.

If on the other hand, if I made the top X (closest the the soundhole) rigid, and made the middle X pliant, I would simulate the double soundboard function of an X braced guitar. .

Keep in mind that the carbon supported braces are much stronger and lighter than spruce ones, and that the interlocked braces move energy freely between each other in a way that joined wooden braces can't achieve. This means that more sound can be produced with less string tension.

In my current designs, none of the braces actually reach the sides of the guitar. This allows some powerful bass to happen but leaves the edges of the soundboard unsupported. The way I deal with this is to use a special heavy lining joining the top to the sides. This lining is a solid wooden construct that supports the sound board in the same way a banjo rim holds a banjo head. The weight of this construct adds to the projection of the whole instrument. Bluegrass banjos use a similar device made of metal to increase power and projection. It is called a tone ring.

I make every other part of the body as solid as possible to reduce any phase cancellation. I use the thickest wood I can bend (about 3mm) and I make the back braces full depth for the whole width and join them to the sides. A Greg Smallman guitar that I played had two backs laminated together in a curve to remove vibration. I find this a bit too extreme (too much weight) for my guitars, but I do it on my mandolins. Designing the body to not vibrate is a principal of speaker box construction. Graham Caldersmith gives a good explanation of this.

Steve Klein was a big influence on my early work. His bracing (below left) uses 'flying braces' going from the bridge plate to the sides without touching the face. These make a hinge to convert the movement of the strings changing length into pumping the sound board up and down. I call this "lever action". The radiating braces pass under the bridge which activates them. The thin curved braces tighten the top, adding to the harmonic content. You can see that there is a treble and a bass side to the top.

Graham McDonald's bouzouki (right) also uses lever action by making the upper part of the X brace heavier and attaching it to the sides near the sound hole. Leaving space between the end of the small braces and the sides will lower the pitch of the top and give the design some strong lower mids. This is an interesting example of mixing a central heavier X brace with supporting lattice braces. Graham has produced some excellent books on bouzouki and mandolin making.

While many makers now use lattice designs in their bracing, it is using carbon fiber above and below the braces that takes it to another level by multiplying the overall strength. The fibers lock the braces together in such a way that the energy moves freely between.

Jim Redgate (left) and Gil Carnal (right) use the fine lattice that is typical of Smallman's nylon string guitars. You can see how Jim isolates the sound hole whereas Gil incorporates it into the bracing as in steel string designs. Note the resulting difference in sound board size. It is important to realize that more sound board doesn't mean more sound or more bass. Note the tone ring and stabilizing braces in Jim's guitar.

There are special properties in a lattice design. If you make up a reinforced lattice, (either free floating or on a sound board) you will find that it can only twist in a couple of ways. Every other form of flexing is prohibited by the lattice structure. The most common types of out of phase sound board movement (top to bottom and side to side) simply cannot occur. That is why symmetry is not a negative factor in these designs. Jim Redgate gives a good explanation. Adding this 'phase control' to the incredible strength to weight ratio of a carbon reinforced soundboard, you can begin to see the powerful potential of this design.

Because I have always used electric and nylon string guitars, I can't play well on heavy steel strings. This is why I felt the need to create a steel string acoustic that felt like an electric but had enough volume to play lead over the top of rhythm guitars. So my focus has been to take the most efficient bracing design known (the carbon reinforced lattice brace) and adapt it to steel strings. Taking the classical lattice brace model above and using it with steel strings doesn't really work as the huge difference in tension changes the whole physics of the instrument.

Unlike the X brace system with it's treble/bass function, I use the whole midrange, expanding it toward the top by the carbon braces and towards the bottom by allowing the edges of the sound board to move freely. This "center weighted sound" is much more like a mandolin or jazz guitar, that use a powerful midrange to be heard playing lead above other instruments.

As you can see from my own bracing design, (shown up the page) I have used some X brace concepts. All of these ideas have to be tested constantly to see if they work, which is why every hand made instrument should be a subtle variation of the one before. This "evolutionary" process is why hand made instruments tend to get better and better while factory instruments at best remain constant, but more often tend to go downhill as production speed and profit margins influence the process.

I will continue to add information to this page and will try to answer questions. I would also love to hear from other makers who can add to my own knowledge.