Listening to guitars made with non-traditional woods

Guitarists (and guitar builders) have been sold and hold dear a lot of misinformation which over time becomes accepted dogma. One such dogma is that dark tropical woods (OK, rosewoods specifically) are required for a great sounding guitar. It should be noted that great builders like Torres have built excellent guitars from domestic woods in the past.

We’ll pass on the question of what constitutes a great sound for now. A more pertinent question is: Is there an objective difference in sound between guitars built with expensive dark colored tropical woods  and those built with cheaper domestic woods ? Do you really get what you pay for or are you just being bamboozled into paying more for the same sound ? The only way to determine this is with double blind studies where listeners don’t know what instruments they are listening to. Many unofficial studies have been done on violins and guitars, and point to the possibility that there is no discernible difference when the only difference is the woods used in the back and sides. This adds credence to the old story of Torres’s paper mache guitar and the idea that it’s all about the soundboard.

Recently the Leonardo guitar research project published the results of an in depth study that into just this question. The study parameters are well thought out and executed. The results are in and it appears to put a nail in the coffin of this old dogma. Read it for yourself here. http://www.leonardo-guitar-research.com/results-online-test-1

The blind audio can be listened to here https://youtu.be/GhssVjSsBKs. I strongly advise listening to this first before watching the video that shows the actual guitars. How many can you pick out ? Do you hear any differences ?

The only remaining question is how long it will take guitarists to catch on and give domestic woods a chance ?

For those wanting to cut to the chase, the following conclusions are directly from the study:

CONCLUSIONS

• All 216 respondents perceived combinations of several guitars (including both T’s and NT’s) as being ONE guitar.

• In this test it was very difficult to differentiate one guitar from the other, and virtually impossible to distinguish between
guitars made from tropical wood species from those made from non-tropical wood species.

• Although several people demonstrated outstanding listening abilities (by indicating 7, 8 to 9 correct transition time points),
the ability to detect the nature of the guitars was notably less pronounced.

• This test shows that the distinctive sound qualities and the supposed nature of T’s and NT’s were not distinguishable one
from the other.

• This test implies that neither group (Tropical or Non-Tropical) possesses inherently distinctive, readily identifiable sound
qualities.
• Indeed, as there are clearly more time points detected between T’s and NT’s made by different builders than time points
between T’s and NT’s made by a given builder, it would appear that the builder may have a more pronounced effect on
differences in sound quality than the wood species used for back/sides, bridge, fingerboard and neck.
    We should, however, exercise caution as some respondents indicated in their comments that they were able to detect
transition points based on “clicks” caused by editing rather than on a perceived difference in sound quality between guitars.
We are still in the process of analysing whether or not there were more detectable “clicks” or other editing phenomena
between different builders than between guitars from the same builder.
• Furthermore, if we consider other studies on this subject (see extra info), the question has to be asked as to whether the
woods for back/sides, bridge, fingerboard and neck are really as important as has been previously assumed.
So after all this you are still skeptical, check out this video of the same guitarist playing a guitar made from newspapers. https://www.youtube.com/watch?v=4Wc5NVyb89Y

New export safe woods

The new CITES treaty updates make export of any and all rosewoods difficult, impossible in some cases. These new rules make it all that more important for guitarists to shed the blinders of convention and learn to listen with their ears instead of their eyes. There are some amazing sounding woods, many with great beauty, just waiting for talented musicians to pick up the mantle and show the world how its done.

In the inventory now are 3 instruments built with readily (and legally) available woods that sound great. Sycamore (known as Plane tree in Europe) has been used in Spain for “low end” flamenco guitars. That is a completely undeserved classification. It is cheaper to purchase than rosewood or cypress, but it is by no means low end in terms of sound. While it is a “white” wood, it should not be limited to the flamenco realm. The two instruments in stock show the best of classical and flamenco characteristics.

Black Poisonwood (Metopium brownei) has been marketed by the false name of Caribbean rosewood (it isn’t a dalbergia sp.) and the unfortunate name of Chechen. Coming from the same family of plants as Poison Ivy (the family Anacardiaceae) the bark of the tree produces urushiol, the same chemical skin irritant that Poison Ivy produces. The wood is safe however, and is one of the most beautiful woods on earth, far exceeding any rosewood I’ve seen. The color is similar to some lighter shades of Brazilian rosewood, but with more depth and movement.

Both of these woods are excellent choices for guitars of the highest quality.

Building a highly responsive guitar: Tops – stiffness vs weight

There are two dominant factors that must be considered when building a highly responsive guitar. The weight and stiffness of the soundboard. These two factors determine the volume and tonal properties of the instrument and while bracing is very important, it can only do so much. It won’t make a poor soundboard equal a great one.

The dance between weight and stiffness is a hard one to master. The best soundboards are lightweight and relatively stiff. The problem is that stiffness and weight are inextricably linked. Reducing the weight of a solid soundboard is normally only possible by making it thinner which makes it less stiff. If it isn’t stiff enough, the tone suffers and consistency suffers more. The result is erratic instruments with loud and quiet notes causing problems with consistent performance. A thicker soundboard will be stiffer and thus less erratic, but won’t have the volume required by today’s demanding musicians. This is the base dilemma of building stringed instruments from solid wood.

My experience has shown that a truly responsive guitar (nylon/carbon strung), in terms of volume requires that a soundboard, thicknessed, cut to shape and ready for bracing should weigh no more than 120 grams for spruce. This will differ depending on the body shape, but it’s a good rough number for this article. Depending on the variety (Sitka, Englemann, European etc) this will be very thin.  As mentioned before, thinner means less stiff and less stiff means erratic results.

The answer to this dilemma for me is composite soundboards. I can meet weight targets while increasing stiffness by building soundboards that are mostly air. More often referred to as “double tops”, the construction is two thin sheets of wood encasing an open Aramid® honeycomb core. The vast majority of weight is in the wood sheets, which must be very thin. Spruce and cedar are used for the outer sheets, which can be as thin as .5mm. Care must be taken when building these tops and proper construction can nearly double the time it takes to build the instrument, but it is worth it. In all cases I’ve built, the finished double-top weighs less and is stiffer than solid tops from the same woods.

Of course it is quite easy to build a bad double top as well. The devil is in the details that take considerable experience to master. I have replaced or completely reconfigured many double-tops in the past decade. Each time the resulting instrument vastly outperformed it’s original setup.

Building a highly responsive guitar: back and sides

Way too much attention has been given to the back and sides in discussions of guitar responsiveness. There are no magic woods that if used for a back and/or sides have any guarantee of tonal quality, volume or responsiveness. For the soundboard you can make a case, but not the back and sides. The reason being that the back is not the primary resonator on a guitar.

But let’s look at the back anyway. There are a few primary functions for the back:

  • The back defines the volume of the body, i.e. air cavity. This results in a major resonance known as the body resonance or the air resonance, depending on who you are talking to.
    • The placement and size of the soundhole is also a factor in determining this resonance.
    • The flexibility of the back also contributes to determining this resonance. A stiffer back will push the air resonance up somewhat and a more flexible back will lower it somewhat.
  • The back itself has it’s own set of resonances. The main back resonance is the least important of the three main resonances; top, air/body and back. However, if it is in the wrong relationship it can cause problems with comparatively loud or soft notes or even causing a specific note to waver.
  • Other than the effect on the resonances, a stiffer back is more likely to act as a reflector. A more flexible back is more likely to act as a resonator. Any back will act as both to some extent, but to what degree depends on the stiffness (and weight).
  • Some woods are highly resonant in the sense that they resonate strongly within a confined frequency range. These woods tend to be very dense and heavy woods, and true rosewoods are in this category. But density alone doesn’t assure a highly resonant wood.
    • In “tap” tests, the unassembled back is tapped and analyzed by how clear the resulting sound is. When viewed on a spectrogram, this is a narrow, sharp peak for the highly resonant pieces.
    • The assumption has always been that the highly resonant back woods are superior, but guitars built with them can be noticeably erratic in the response, volume and sustain of individual notes.
  • Other woods are much less resonant, and will resonate more evenly across a broader spectrum of frequencies. Woods like maple are in this category. Lower density does not guarantee this kind of  response characteristic.
    • This actually makes for a more balanced guitar, with fewer hot notes and fewer dead notes overall. It’s still possible to have these problems if the overall frequencies are in conflict.

I categorize back/side woods according to density, response type and appearance. Appearance being unimportant to sound.

Building a highly responsive guitar: The bridge

The stiffest and heaviest brace on a guitar is the bridge. Changing the mass and/or the design of this important element will have discernable effects on the sound of the strings.

  • A relatively heavy bridge will cause the attack to be slow compared to a relatively light bridge, which conversely will allow for a faster attack. This results in a duller sounding attack.
  • A relatively heavy bridge will also reduce the overall volume as it takes more energy to move a heavier object than a light one. Thus a heavier bridge makes for a less responsive guitar.
  • However the law of inertia implies that it will also take longer for the heavier bridge to stop vibrating (An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.) So the heavier bridge augments sustain. How much that matters with the weights involved here is debateable.

Taking all this into account, my approach is to go for maximum attack and volume by using relatively light weight woods for bridges. When using heavier woods like rosewood, my target weight is 20 grams for the bridge, not including the saddle, but this is an elusive target and can result in very thin bridge wings. Using a lighter wood like sapele, I usually get a bridge weighing 14 grams, which includes a tie block overlay of a very dense wood like ebony or gidgee. I also save a few grams by making the saddle from a dense wood like african blackwood or snakewood. The end result, when used in conjunction with properly built composite soundboard with diamond bracing is a very loud and responsive guitar. No one has complained of lacking sustain on these instruments.

Note: About the Kasha bridge design.
I have a few things against the Kasha bridge design, which I have used in the distant past. The primary issue is weight. In order to create the large surface area of the bass side of this design, that side at least must exceed my weight target(s) significantly. The treble side is not that much smaller than a traditional bridge, and I can equal or better the weight of that side by using a lighter material. I don’t actually believe that the two piece bridge concept has any appreciable positive effect when mounted on a top that is not separated. The whole top vibrates regardless of the number or size of the bridge sections. I understand the rationale for the design of this type of bridge and how it relates to the overall Kasha system, but my experience is that complete adherence to the overall design is not necessary to benefit from the insights contained in the concept.

Building highly responsive guitars: Bracing

The road to building exceptionally responsive classical guitars is littered with failed attempts and discarded theories. As I experiment a lot I’ve had my fair share of both. But scattered among my failures are diamonds that have pointed the way to designs, materials and processes that consistently result in instruments deemed extraordinary by experienced professionals.

The bracing pattern outlined above is the basis for the most recent, and most highly acclaimed series of guitars I’ve built. I refer to it as the Spyder pattern. I seldom build two identical instruments, but all the Spyder braced guitars have this common conceptual beginning. This design is extremely flexible and seemingly minor variations, like the size of the center diamond, can have very discernible effects on the sound of the instrument. 

When paired with a composite soundboard, and properly constructed, this pattern is a great platform for a highly responsive instrument.

2017 – Changes to the lineup

During the past few years  I have revamped the line of guitars that I will be offering going forward. The new lineup features:

  1. “Double Top” soundboards are now standard on classicals.
  2. New bracing specifically designed and tested for Double Top construction.
  3. French polish finishes.
  4. 5 piece neck shafts. More stable and less likely to absorb too much vibration.

The move to double top technology is based on the superior performance I get using it. Demonstrably louder, more balanced with greater overhead than my solid top instruments, this is an obvious move ahead of the pack.

New soundboard materials require new bracing strategies, like my split diamond bracing. The results of this flexible fan/lattice/kasha hybrid has produced exceptional results and we’ve just begun to explore the possibilities.

Years working with toxic finishes has left many luthiers physically weakened or dead. The only rational response is to return to the only truly nontoxic finish, shellac, aka French polish. Always the best finish acoustically, it does require more care than synthetics​.