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 the back is under tension, which prohibits free vibrations. It is not optimal. I have designed a super light, very strong carbon fiber beam that goes throughout the length of the box. Its only function is to counteract 100% of the string tension. The carbon fiber beam in my guitars works similarly to the wooden central block in Gibson ES-335. However, it weighs only slightly over 100 g (3,7 oz) and does not touch the top or back plates, leaving them free to vibrate. I thought about this solution for years but hesitated as I have not seen any examples of this. I finally came across Kim Walker's Solo Novo archtop. Kim used a similar concept, but the beam in Solo Novo is of balsa, spruce, and a little graphite. Kim Walker developed this solution when the customer told him: “Build the best archtop you can”. I was hooked.
There is no sound hole in the top of my guitars. The sound hole acts similarly to the resonance hole in bass-reflex speakers and 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 sound 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 the garden for children to play during hot summers. When one drops something heavy in the middle of the pool, the waves on the water go outside from the center and are hitting the pool sides. As the sides are elastic they start to “swallow” the waves’ energy. They are 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 the water and vinyl sides are similar. The effect is fast wave cancellation.
Now imagine a proper concrete-walled, swimming pool. When you toss a stone on calm water you can see the waves traveling from the place the sone hit the water outside in the concentric circles toward pool walls. Then they are almost perfectly reflected from the walls. The concrete is not compliant to waves. We say the impedance difference between water, as a wave-transferring medium, and concrete is large. The waves can be reflected many times from the pool walls until they disappear.
When a string starts to vibrate after the guitar player hits 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, travels from the bridge toward the sides of the guitar. When the wave hits the guitar side, its behavior depends on the impedance mismatch between the spruce top, as a wave transferring medium, and the sides.
When the impedances of the top and sides are not very different, a lot of energy is compliantly drawn from the top by the sides. Many argue that this transfers energy to the back, but in reality this is not very efficient energy transfer. The vast majority of top and back coupling is through the air pressure changes in the box.
When the impedance mismatch between the top and sides is large, the sound wave in the top is reflected and propagates from the side, then reflects 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.
Desirable large impedance mismatch between the very light spruce top and guitar sides can be achieved by enlarging sides mass (see Trevor Gore’s book on guitar design: https://goreguitars.com.au/the-book/), stiffness, or both. I do want my guitar to be light, so I chose to increase stiffness. I make the sides from a complex laminate of wood veneer, many layers of carbon fiber fabric with fibers laid in the strategic direction, and Nomex as a spacer. This is manual work that requires many days. As a result, the sides are rigid like concrete, particularly 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 canceled.
Rigid neck
Designing a neck that does not vibrate and absorbs energy from strings is a challenge. I am a glider pilot, and I have borrowed upon the brilliant design of Diana 2 glider wings in my neck design. BogumiÅ‚ BereÅ›, the Diana 2 structural designer, didn’t use the heavy spar traditionally used in glider construction. Instead, he came up with a multi-web-box design similar to corrugated cardboard. The effect is the lightest glider in the 15m class (182 kg compared to an average of 240 kg). While the wings have the same rigidity and toughness as competitors, 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.
My neck is designed based on the brilliant design of Bogumił Bereś.
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.
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Meticulously chosen wood
I make my guitar tops and backs from carefully chosen wood. For spruce tops, 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 consideration its acoustical capabilities (maximizing radiation ratio) than esthetics only. The back, through supporting the top resonances, can color the guitar sound 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 the top and back before the 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:
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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 fibers are less cut while shaping the plates. Longer wood fibers that follow the plate shape make a stronger and lighter plate. I do not hesitate to thin the plates in some areas to 1.5mm (less than 1/16 of an inch).
Choose materials by their 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 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.
Very-low impedance humbucker
Yes, it is quite an extraordinary pickup in Blue Arch Guitars archtops. I shall explain why.
There are several reasons why I designed the pickup for my guitars differently. The main is the same as why I design my guitar differently. Traditional archtop guitars were designed using materials, technology, and knowledge available at the time of their creation. Lloyd Loar designed the Gibson L5, the archetype of all traditional acoustic archtops, 100 years ago. Over 100 years, our knowledge of materials science and acoustics has advanced, and although many guitars built with old technologies sound great, they have their issues due to the materials used. Good quality wooden soundboards are responsible for the great sound of the instruments, and with good reason - there is no better material for sound radiation. But wooden structural elements are subject to long-term deformations - creep. The guitar can be redesigned to take advantage of new materials and technologies. Just like other utility products. Who uses wooden tennis rackets, wooden skis, or leather ski boots today? I build load-carrying structures in my guitars from aviation-grade carbon fiber composite. They can be lighter and stiffer, and they never creep.
The same idea, to use current knowledge, stands behind my pickup design. The pickup coil is inherently symmetrical and balanced. I have never understood why guitar pickup designers are changing this to unbalanced already in the guitar cavity. The unbalanced signal and high-inductance coils are a recipe for problems with mains hum and electromagnetic interference. Additionally, the high impedance of the coils and high capacitance of the guitar cable heavily limits the frequency response of the pickup. This combination creates a known vintage sound that has nothing to do with the acoustic sound of the instrument. I wanted to design a pickup that would support, not replace, the acoustic sound of my acoustic archtops played with acoustic phosphor bronze (ideally 12-53) strings. A pickup that will not be sensitive to hum but also to electromagnetic interference and will enable the use of long cables without affecting the frequency response. Just like high-quality microphones. And I wanted a wide-frequency response pickup that would process high harmonics and partials. Of course, this is not the sound of an acoustic guitar. To reproduce the nuances of the soundboard sound, you need a microphone. It is my next development project - a pickup + built-in microphone inside the instrument. Will come.
The pickup designed by me is a very low-impedance humbucker. The humbucker is responsible for reducing hum from the mains. The DCR of 60 Ohms and low impedance, less than 250 Ohms in the acoustic band, similar to the impedance of professional microphones, together with the balanced connection, allows for reduced electromagnetic interference. At the same time, the frequency response is flat over the entire audible frequency range with a resonance frequency above 20 kHz. These qualities allow the musician to shape the sound in an amp. The guitar connects directly to an XLR microphone input in an amp (preferably, due to high-frequency response, an acoustic amp), into the PA system, or through the supplied Shure A95 impedance matching transformer to any instrument input of a guitar amp (again - preferably an acoustic amp).
Here are some recordings of my archtops with the same pickup by Kinloch Nelson, Tony McManus, Tim Lerch, and Mark Dziuba: