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Paul La Valle - Luthier

Improving the Acoustic Guitar Neck Block

I recently wrote about how I borrowed a stethoscope so I could listen to the inside of several guitars and the guitar's soundbox. What had I found was interesting in that the sound was most loud in the lowest bout, and actually deadened to almost no sound the closer I came to the neck.

It seems that since the neck has no "connection" to the soundboard, the sound tapers off and is lost at this point.

Since my last article, I have had some serious downtime, and with that I had more time to study sound and acoustic properties. Sometimes minor setbacks can lead to amazing discoveries!

In the previous article I made mention that the guitar is not an amplifier — which would require a power supply. Rather than amplify, the guitar dissipates most of the string's energy, causing the guitar to warm 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.

AND it is at this point that my research found the energy dissipating falls short of return to the nut.

Think of the string as a ripple moving across a pond and returning to the starting point. This is known as the fundamental vibration of a string [figure 1].

FIG 1.

An ideal vibrating string will vibrate with its fundamental frequency and all harmonics of that frequency. Each of these harmonics will form a standing wave on the string.

Much has been done over the past few centuries in the study of wood and its tonality, its bracing and the acoustic properties of the violin; and anything and everything you can think of that goes into making a violin, yet it's only the past couple of decades that more research is being performed in studying the acoustic properties of the guitar.

Over the past century, luthiers have pretty much followed the same principles of guitar building as they did when they were first invented. Only in the past few decades have they started changing how the bracing structures are formed, the linings that are used or side bracing and kerf placement (facing in or out).

Yet, I have never seen anyone really do much with the neck block, or at the very least, not as I have been developing on my theory.

Study of the Neck Block and Upper Bracing

The neck block is a crucial structural portion in the guitar build, as it provides a stable and solid base onto which the neck is joined to the body.

That's, it. As important as it is, that is all the neck block's function is purposed for.

What I am doing is removing the upper transverse brace/graft as well as the fingerboard brace (just above the sound hole). These two braces assist in keeping the soundboard from splitting, and serve no other purpose other than protection.

FIG 3.

Some builds eliminate the transverse brace altogether, while some cutaways will use half the transverse to assist in supporting the soundboard.

In my build I could have used the fingerboard brace and half of the transverse brace, but that would have been following the same old – same old, and that would defeat what I am working to accomplish, which is to hopefully have the sound resonate in the upper bout – thereby increasing the breadth of the instrument and offer a more rich and full sound.

It is designed so the neck block integrates with the upper bout bracing and forms the sound hole brace. The expectation, I set in my previous article, is to hear sound in the upper bout of the guitar because now the neck, block and bracing form a single unit.

The additional benefit I get from this design is the rigid brace for the cutout section and horns, ensuring they will never break or crack.

Sound Falls Short

In my previous article I mention that 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. Figure 4 demonstrates my point and how the sound (in blue) deadens.

FIG 4.

Everyone has done the tried-and-true single neck block. But is it truly tried AND true?

Figure 2 shows a standard dove tail and standard bolt-on neck block including the neck.

FIG 2.

I believe the kinetic energy of the strings is lost doing it the "traditional way" in the upper bout register of the guitar. Traditional bracing doesn't allow for it to be captured from the neck through the strings and carries it to the bridge and the soundboard. I'm expecting it to be carried through my bracing as well as the strings to the soundboard coupling it back and forth and giving you a full sound.

As the vibrations leave the fretboard on traditional builds, the soundboard is floating over two thin strips of wood, it travels to the bridge and back down to where it dies down before reaching the fretboard.

In the LaValle Guitar build, the fretboard is integrated with the bracing, neck and neck block – allowing for the vibrations to roll down to the bridge and back to the fretboard, producing a full, thick, rich sound. Additionally, this piece also forms the foundation for the side support, again this ties all of this together allowing for the kinetic energy to be fully felt by the instrument and produce that full rich sound I am hoping to achieve.

FIG 5.

Stay tuned…