CAT Scan of a Vintage Martin Guitar


My interest in the science of sound grew out of my inability to understand most of the theories or philosophies of modern luthiers. One issue I’ve struggled with is why so many of the best examples of vintage guitars that are impressive on so many levels are now approaching 100 years old. Why doesn’t the same abundance of great-sounding instruments exist in the modern era? Something was definitely right with those old guitars. But when the stars of tonewood are aligned, modern luthiers are sometimes close to hitting that target, so I don’t think it’s totally a matter of these older instruments maturing through aging. I feel like these guitars were good from the start.


So what should I do to reproduce the sound of these old guitars? And, more importantly, what sound is my main focus? I’m sure I’ve said this before, but, just in case, I’ll say it again: the sound of world-class musical instruments is not subjective. Either they fall into this category or they don’t. However, there are still slight variables at play.

When I was developing my acoustic guitars, I had a blank canvas. All I had to do was tweak until the voice of the instruments made me happy, and it became my sound. This method is called “form follows function” because I tweaked the components until the instrument worked for me.

Reconstructing the sound of existing instruments is a more difficult task. In order to pull it off properly, you need to replicate all of the components dimensionally, inside and out. Then you can manipulate the tonewood to adjust the sound. It’s “function follows form”, which is a very different and ultimately more difficult style of musical instrument making. In my shop, we call this style of backdoor guitar building “reverse profiling”.

At the time, I managed to do this with Gibson Advanced Jumbos and vintage J-45s, but the Martin sound was more elusive. The added mass of taller braces and thicker tops can easily become sluggishly dark and less responsive. But if properly balanced, it’s a pretty special sound. Recently I decided to take the sound reproduction of vintage Martin guitars to the next level, specifically the Martin D-18 from the late 30’s.

Unlike a modern sound which is commonly described as moist or lush, vintage sound is clear and dry.

I have always been impressed by the sound of vintage guitars. Unlike a modern sound which is commonly described as moist or lush, vintage sound is clear and dry. If we can pin down this sound, we will have a better understanding of tonewoods and their stability. This is just the start of a much larger picture that will unfold over the next few years, and this 1937 D-18 is just one of the projects underway. So far, our findings and progress are encouraging. I can’t wait to see where it ends, but I expect good things.

The first order of business was to locate a specific example that had the desired sound and feel. There are different sound examples from any period, so a marker was needed to keep the project on track and to compare accuracy. This kept the project honest. I chose two models to compare: a 1937 D-18 with advanced bracing and wide string spacing, and a 1939 D-18 with non-advanced bracing and narrow string spacing. These were two iconic examples that had unique tones and folklore associated with their bracing patterns.

The next step was information gathering. Reverse profiling is trickier than new construction, and we need to understand the materials used a century ago. The data we compile plays a major role in the tonal development of the instrument and is absolutely necessary before profiles can be developed. To achieve this, I worked with fellow luthier Tom Nania to CAT (Computed Axial Tomography) scan our vintage marker guitars. This way, we could calculate the density of vintage tone woods. Next, we physically mapped the weights and thicknesses of the guitar inside and out. This generated the preliminary formula which was a key step in reverse engineering an existing guitar for reproduction. We have established a definite path or, in other words, a recipe. When we make a change, which is inevitable, we will have clear benchmarks for each attempt.

I have always been impressed by the sound of vintage guitars. Unlike a modern sound which is commonly described as moist or lush, vintage sound is clear and dry. If we can pin down this sound, we will have a better understanding of tonewoods and their stability. This is just the start of a much larger picture that will unfold over the next few years, and this 1937 D-18 is just one of the projects underway. So far, our findings and progress are encouraging. I can’t wait to see where it ends, but I expect good things.

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