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Can An Acoustic Guitar Be Improved Upon?
To answer this question, I spent the past few months studying acoustic principals and specifically how they relate to the guitar – form/shape, wood, bracing, etc. To start, I found that the study of the acoustic principals of the guitar is only in the past few decades, while the same study on violins has been over the past century. It appears that many luthiers are satisfied with the status quo, and that's OK as the old saying goes "If it ain't broke don't fix it."
But I like to break things only to see how we can better improve the item.
Let's break down how an acoustic guitar creates it's sound, and see if we can improve the sound acoustics. First, the guitar is not am amplifier of the string signal and that the sound board is not the sole sound generator. The guitar cannot be acoustically subdivided into treble and bass sections, and the neck in fact is acoustically active. The sound does not travel in waves radiating from the bridge, nor travel down the braces like a train on tracks.
The guitar, in it's most simplistic way, is a tool built to release the kinetic energy found in the strings, and convert that to a controllable audible sound. When strings are tightened and plucked, they create pulses of sustaining signals. The frequencies of these various and distinct tones are related mathematically rather than randomly. All of this is transferred to the soundboard and neck via the bridge, saddle and nut.
The guitar is not an amplifier — that would require a power supply. So, rather than amplify, the guitar dissipates most of the strings energy, causing the guitar to actually warm up as it is played. Only a small amount of energy from the strings leaves the guitar. The structure of the guitar transforms that fraction by the energy storing and discharging process called resonance.
A lot of this got me thinking about how the neck attaches to the body. In the electric guitars I have built, some are two pieces of tone-wood joined together with a dado joint and a hard rock maple spline – just as the necks are made from. I found that the sustaining properties of the string carried longer on these more than models built of solid wood. Even more so then thru-body builds. I suspect it has to do with the transfer of energy between the woods. I'll probably research that at another date.
I watched a luthier session when the instructor had the students 'listen' to the change in sound from a small music box, when placed on the acoustic guitar strings. Laying the guitar flat on a table, he played the music box – and it was audible, but when he placed it on the strings over the hole, the sound increased, by using the strings vibration and soundboard. Interesting! The music box was louder — not amplified — just louder, more full and rich in sound.
Now back to "A lot of this got me thinking about how the neck attaches to the body."
I recently borrowed a stethoscope so I could listen to the inside of several various guitars and the guitar's soundbox. What I found was the sound was most loud in the lowest bout, and actually deadened to the point of almost no sound the closer I came to the neck. Interesting! It seems that since the neck has no "connection" to the soundboard, sound is lost at this point.
I am going to test my theory, where I remove several bracings from the soundboard near the neck, and sculpt a contoured brace from Mahogany, with several areas cut-out to allow for sound resonance to the board, and brace the structure. Additionally, integrated into this is the neck block to which the neck attaches – both are made from the same Mahogany. Mahogany will be used in constructing all bracing.
To create the side support, I am using maple (high in tone), which will run the full height. The sides are Walnut (a low moody sound) The kerf will face outward (see image below, lower bout right side), leaving a smooth interior wall for sound to flow off. I am contouring all braces, so there are minimal to no sharp corners. I believe sound flows better over smooth surfaces – and by turning the kerf the opposite way, it also removed channels where sound is trapped and dies – and instead themselves acting as tiny resonance chambers. Finally, a light coat or two of shellac which seals the wood on the inside from moisture and to allow sound to better move freely.
The added tonal properties — I hope — will increase the breadth of the instrument and offer a more rich and full sound.
