Aaron regularly uses tea leaves to predict the future! He is not seeking the winning numbers of the next Lotto Texas drawing or trying to predict what the stock market will do next week, or whether it will rain next Sunday night (although that would be handy information). You see… instead of being a tasseographer, who seeks to predict the future by using superstition and folklore, Aaron is a luthier who uses science to make predictions about how his hand crafted classical guitars will sound. He is also a classical guitarist. He knows what he wants to create both visually and aurally. He knows how the guitar needs to feel in a guitarist’s hands. Yet even with all these artistic skills there is more to know when creating a high end classical guitar. Lutherie is tedious, time consuming work and one mistake or bad judgment can cost you six weeks worth of time and hundreds of dollars in material costs. The bottom line is that Aaron wants to be able to know with some degree of certainty that as he carves, sands, scrapes, shapes, assembles and configures the components which eventually become a beautiful classical guitar, it will also be the best sounding instrument possible. This is where the tea leaves come in.
How a Classical Guitar Works
The amplification of the vibration of the strings on an acoustic guitar is caused by a transfer of vibrational energy from the strings to the soundboard (the top plate to which the strings are attached). From there it is transferred into the resonant cavity formed by the body of the guitar and into the air in front of and around the guitar. These components act very much like a loud speaker but are more complex because not only do they amplify the sound vibrations, they also add harmonic overtones which the listener interprets as the tonal quality of the guitar. The back of the guitar also contributes to the amplification to a lesser extent. All the components used in a guitar contribute to many other acoustical properties of the guitar like tone, sustain, harmonics, etc. It is the careful manipulation of several design parameters that allows Aaron to create the impressive beautiful sound of a Wood Ring guitar.
Testing and More Testing
There are many processes and tests that we perform throughout the process of building each guitar that guides us toward the final great sounding product. Initially there are several tests that are used to evaluate each piece of wood being considered as a component of a guitar. Not only must the wood be visually appealing, it must have properties that are conducive to the production of the sound Aaron is looking for in his guitars. For instance, he is looking for pieces of wood that have a high strength to density ratio. This has to do with the need for the guitar to be light as possible in the hands of the player and yet strong and durable. A high strength to density ratio also allows stronger and longer lasting sound production with less energy input from the player. He is also looking for wooden components where the internal damping of sound is minimal. This means that when energy is put into the guitar to make it vibrate, that the loss of energy to heat through internal friction is minimized.
As construction proceeds, tests are done to guide us at each stage of construction toward the finished product. One test that we rely on is a process called Chladni testing of the soundboard. Of all the components of a classical guitar that the luthier creates, the soundboard arguably has the most influence on how the guitar sounds. The magic is in how the soundboard responds to vibrations. Sound vibrations transferred to the soundboard (either by guitar string or by loud speaker) occur as standing waves across the two dimensional surface. Since the vibrations are fast and the amplitude of the waves are very small, we must use an indirect way of seeing them. This is where the tea leaves used in conjunction with Chladni testing comes into play.
- Graph showing the oscillating nature of a sound wave.
Great care is taken in the selection of the tonewood to be used as a soundboard as well as in the construction of the soundboard. We use Chladni testing to help us visualize and identify the resonant harmonic patterns that the soundboard favors. Every piece of wood used as a soundboard favors certain sound frequencies. The complete set of frequencies that a soundboard favors is like a voiceprint. It is a unique acoustic signature for each piece of wood used. It is the luthier's job to evaluate and manipulate these signature frequencies to create a soundboard that brings out the full potential of the piece of wood that becomes a soundboard. It is the combination of these favored frequencies that experienced luthiers listen to when they tap on the wood to hear the wood's tap tone. It is also the manipulation of these frequencies throughout the building process that helps the luthier create the optimum sounding guitar.
This Chladni testing process takes advantage of a phenomena called Chladni patterns. These patterns were discovered by a man named Ernst Chladni (pronounced Klahdnee) (1756-1827) who was a German physicist and musician. He has been called the "father of acoustics" because of his major contributions to the study of sound. He discovered that by drawing a violin bow across the edge of a thin plate of wood it would vibrate. When he placed some sand on the plate, he was able to create patterns by creating vibrations at different frequencies. Different patterns were created depending on the shape of the plate. See the images below. The rectangular plate images of Chladni patterns were created by John Tyndall in 1869. The circular plate images are from Chladni's work on the subject.
The geometry of instruments like the guitar and violin generate patterns similar to both rectangular and circular plates. Different types of materials produce differing patterns as well. We have found that different species of woods can produce dramatically different patterns as well for a given shape. There are many variables that can affect the patterns during the testing process as well. Things like speaker location, how and where the plate is supported must be carefully controlled during testing so that repeatable and comparable results can be recorded and analyzed.
What is important to the luthier is that these patterns demonstrate visually how the sound waves travel through the plate. The places where the sand remains are the nodes of the wave pattern (where there is no vibration). The places where there is no sand are the anti-nodes of the wave pattern (where there is vibration).
Violin makers were some of the first luthiers to use this phenomena to fine tune their instruments. This process was documented in an article of Scientific American written by Carleen Hutchins a renowned violin maker who made huge contributions to the science of plate tuning of violins using Chladni patterns. This article described how these patterns can be used to guide the manipulation the top plate thickness to get an optimal sound.
Tests Performed in Crafting a Wood Ring Guitar
Our testing apparatus consists of a stand that we built for this specific purpose. It is based on a design described in the book called "Left-Brain Lutherie" by David C. Hurd, Ph.D. David is a master at building Ukuleles. His book is a classic with regard to using the scientific method in the construction of stringed instruments. The guitar plate to be tested is placed on two tightly strung rubber bands one supporting the plate on each end. A speaker is placed under the guitar plate and is driven by a computer program which produces tones at any frequency the user desires. We place tea leaves on the plate to show the patterns. Sand, salt, glitter and saw dust have all been used to create Chladni patterns but we have found ground tea leaves to work very well for our purposes. The full range of frequencies that a guitar can produce are scanned and the frequencies of the patterns are recorded along with the geometry of each pattern.
The following is an image of some Chladni patterns we found for a rectangular piece of German Spruce that we will be featuring in a guitar Aaron is currently working with. This is a representative set of quality control tests that we perform on all pieces wood being considered as a soundboard for a Wood Ring guitar. As you can see, the higher energy frequencies produce more complex patterns.
As the building process proceeds we again perform more Chladni pattern tests on each soundboard. We identify certain dominate patterns over the frequency range of the guitar that we can follow throughout the building process and watch how their absolute frequencies change as well as how their relative frequencies change. This information guides Aaron in the actions he needs to coax each guitar toward the sound he is seeking. The photos below show some of these patterns.
There are many luthiers that use the process of Chladni testing to create the outstanding guitars that are made around the world. No one learns something this complicated without some help. Some of the luthiers that greatly influenced Aaron's learning process are listed below. We wish to thank them for having the self confidence and generosity to share some of the knowledge they have spent so many years to develop so that others may stand on their shoulders to take lutherie to the next level.
Brian Burns - Brian's website was influential in helping shape our testing program. He has always been very encouraging in our correspondence with him. Brian does consulting and also has some very nice lutherie tools for sale at a reasonable price.
Ervin Somogyi - A class act with regard to lutherie. Many of today's luthiers have learned from Mr. Somogyi.
Luthiers of North Texas (LINT) - This is a group of luthiers who meet every two months in the Dallas - Fort Worth Area. One member in particular, Derek Lambert, is a very good friend whose ideas, feedback and conversation in general are all greatly appreciated.
There have been many fine classical guitarists in Texas that have been kind enough to play Aaron's guitars and give him very candid and valuable feedback as to what they are looking for in the ideal guitar. Here are a few that we would like to give special thanks to.
Fernand and Olga Vera - These are two dear friends that are amazing classical guitarists. Be sure and see them in concert or when they are playing at many of the local guitar festivals. Also don't miss a chance to attend their annual workshop.
Eddie Healy - Eddie is the Coordinator of Guitar and Music Theory Studies at Eastfield College in Mesquite, TX. And, he also teaches at The University of Texas at Dallas and the Gray School of Music. Eddie is the director of the Brookhaven-Allegro Guitar Orchestra, a community guitar ensemble in Dallas that meets and performs regularly at Brookhaven College. He has served as the assistant festival director at the Texas International Guitar Competition/Festival since 2010 and is director of that festival’s youth competition. In 2016 he was named the Director of Education at the Annual Classical Minds Guitar Festival and Competition. We are grateful to him for all the great feedback.
Will Douglas - Will is currently Artist in Residence at Scarborough College at Southwestern Baptist Theological Seminary and as an Adjunct Instructor of Music at Weatherford College, Arlington Baptist University and Tarrant County College Northwest and a private guitar instructor at The Guitar Studio in Fort Worth, TX.
Cymantics - A branch of science emerged in the 1960's called Cymatics. It is the study of visible sound and vibration. This is a field of study which was named by Hans Jenny emphasizing the intersection between art and science in the study of unseen phenomena like standing waves in various types of media.
TED Presentation About Cymantics by Evan Grant - A wonderful talk at the TED conference in July 2009 given by Evan Grant about Cymatics (the study of visible sound). It has some great demonstrations of Chladni patterns and how this study of the substance of things not seen is being applied in research around the globe. It is for instance being used to create a lexicon of Dolphin language and is also allowing artists to create wonderful art from different music sources from Beethoven to Pink Floyd.
How Guitars Work - Describes how classical and acoustic guitars work.