Design principles:
Free the guitar top and back!
The most important function of the guitar top (and back!) is to translate the string vibrations through an efficient bridge into musical sound. Traditional guitar construction uses a closed guitar box as a structure opposing the constant ~75kg (or~165 lb) string tension. The top is then in constant compression and back tension, which prohibits free vibrations. This shouldn’t be so. I have designed a super light, very strong carbon fiber beam that goes into the box length. Its only function is to oppose 100% of the string tension. Similar to wooden block 335 has inside the box, but the CF beam in my guitars weights slightly over 100 g (3,7 oz) and does not touch the top or back leaving them free to vibrate. I was thinking about this solution for years but was hesitating as I haven’t seen any examples of this. Then I saw the Solo Novo archtop by Kim Walker, which uses a similar concept, but the beam is made of balsa, spruce and, a little CF. Kim Walker went on this path in a guitar, where a customer told him “build the best archtop you can”, I was hooked. If Kim Walker decided to do that, there is something in the concept.
There is no resonance hole in the top of my guitars. The resonance hole emits low frequencies only up to maybe 200 Hz. The low frequencies are emitted omnidirectionally. Middle and especially high frequencies are emitted directionally – in front of the guitar. There is no good reason, except for tradition (OK, there is a reason for f-holes, but this we will discuss further on) to put it in front of the guitar using the most precious area of the guitar: the vibrating top. The resonance hole can be safely placed on the side of the guitar making a vibrating top bigger and thus more efficient.
Rigid sides
Imagine a small swimming pool with vinyl inflatable sides. The kind we place in garden for children to play during hot summers. When one drops something heavy in the middle of the pool, the waves on the water goes outside from the center and are hitting the pool sides. As the sides are elastic they start to “swallow” the waves’ energy being compliant to waves. Soon the wave is cancelled. It is quite easy to move the vinyl pool sides by water. We say that the impedance of water and vinyl sides are similar. The effect is fast wave cancellation.
Now imagine a proper, concrete walls, swimming pool. When you toss a stone on a calm water you can see the waves travelling from the place the sone hit the water outside in circles towards pool walls. Then they are almost perfectly reflected from the walls. The concrete is not compliant. We say, the impedance difference between water as a wave transferring medium and concrete is very big. The waves can be reflected many times from the pool walls until they disappear.
When a string starts to vibrate after guitar player hit it with a plectrum or finger, the string vibrations are transferred to the bridge and then, from the bridge to the top. The wave, similar to that on the water in a pool, is travelling from the bridge towards the sides of the guitar. When the wave is hitting the guitar side, its behavior depends on the impedance mismatch between the spruce top, as a wave transferring medium, and sides.
When impedances of top and sides are not very different, a lot of energy is compliantly drawed from the top by sides. Many argue that this transfers energy to the back, but in reality this is not very efficient energy transfer. Especially in the low/medium frequencies, where the back can support the overall guitar tone. Vast majority of top and back coupling is made through the air pressure changes in the box.
When impedance mismatch between top and sides is big, the sound wave in the top is reflected back to the top and propagates from the side, reflects back on the other side of the guitar and so on. On some frequencies, standing waves have maxima. They are described by their peak frequency, loudness and width of the peak. At low frequencies we call them signature modes. At higher frequencies, formants. Every instrument has a characteristic set of signature modes and formants making its timbre unique.
In the same way, the voice of every person, due to the differences in the structure of the larynx, is characteristic through its signature modes and formants.
Big impedance mismatch between very light spruce top and guitar sides can be achieved in two ways - by making sides heavy (see Trevor Gore’s book on guitar design: https://goreguitars.com.au/the-book/), or stiffer. I do want my guitar to be light, so I make the sides from a complex laminate of wood veneer, many layers of carbon fiber fabric with fibers laid in the strategic direction, nomex as a spacer; a lot of manual work over many days. The sides are rigid like concrete, especially in the direction opposite to sound waves hitting the sides’ walls. I designed them to have minimal compliance in that direction, so the standing waves can be supported, not cancelled.
Rigid neck
Designing a neck that would not vibrate drawing energy from strings is a challenge. I am a glider pilot and I have used the brilliant design of Diana 2 glider wings. Bogumił Bereś, Diana 2 structure designer, didn’t use the heavy spar, a traditional design in glider construction. He has designed a multi web-box design, we can see something similar in corrugated cardboard. The effect is the lightest glider in the 15m class (182 kg compared to an average of 240 kg). It has wings of the same rigidity as its competitors, but they are 50% lighter. Look at the picture - I have just landed from a high-altitude flight and you can see (besides my dear friend, Sebastian Kawa, sixteen-time World Champion in Gliding) the water condensation in places where the internal structure still keeps a low temperature.
Picture above - source:
The design of the Diana 2 wing is similar to the drawing shown here.
The authors of this paper checked the efficiency of 3 different wing designs and found this one superior to the others.
My neck is designed based on the brilliant design of Bogumił Bereś.
Meticulously chosen wood
I make my guitar tops and backs from carefully chosen wood. For spruce, I go for rigidity and lightness. I measure the speed of sound and density of every spruce piece and chose the specific pieces taking much more into consideratin its acoustical capabilities (maximizing radiation ratio), than esthetics only. The back, through supporting the top resonances can color the guitar sound quite substantially. Every piece of wood, even of the same species, requires different thicknesses to couple with the top in the right way.
Bending wood for top and back before final carving
I do carve the top and back to the final dimensions after the top and back blanks are bent. I use the method of Helen Michetschläger, which she has described for violas here:
https://helenviolinmaker.com/wp-content/uploads/2017/04/Dartington-talk-transcript-with-pics.pdf
What I find convincing in this method is the fact that through bending the wood fibers follow the shape of the board, hence, the wood fibres are less cut while shaping the plates. Longer, following the shape of plates wood fibers, resulting in stronger plates, that can be lighter. I do not hesitate to thin the plates in some areas to 1.5mm (less than 1/16 of an inch).
Choose materials by its engineering qualities and beauty
Materials used in my guitar build are different than many guitar builders use:
I use wood for its beauty as well as for its unique engineering qualities. As Ken Parker once said, if there was no wood and someone would develop it, he/she should get a Nobel Prize for it. Wood is such an incredible material!
Whenever I need high strength and stiffness in a specific direction I use carbon fiber laminate.
Aviation grade aluminum 7075 is used for its excellent mechanical properties, high strength, toughness, and good fatigue resistance.
Some applications requiring metal cannot be efficiently made with aluminum. Steel is an amazing material. If you need isotropic strength, there is no better choice than steel or high-strength titanium alloy. I have used both in my guitars.
I also use brass, silver and aluminum bronze.
Pickup.
Although my archtops are acoustic instruments, I envision adding a pickup. I have designed an ultra-low impedance (DCR 60 Ohms) humbucker, which translates the whole frequency range of strings and is noise silent. Traditional pickups developed for jazz archtops in the 40s and 50s are what they are because they reflect the level of technology of magnets and guitar amps avaiable at that time. Guitar players love that old sound because their heroes were using that sound due to available equipment. I respect that.The beautiful mellow tone of the old jazz archtop is a standard. But as my acoustic archtops generate a lot of high-frequency aliquots, I wanted to design a pickup that would pick them all. Or at least most of them. If you would like to have a pickup in one of my guitars, please consider the full frequency, noiseless pickup I have designed.
Take a note that the pickup is balanced to work with bronze acoustic strings. I am using D'Addario EJ16 or EXP16 (12-53).
