Mandolin Measurement Project Overview

My Research Project - Blog 1

               Once you figure out how to build a mandolin by making all the parts and then glue them all together, you can begin thinking about how to make the next mandolin better.  

              But...

              Better how?

              This is an important question!  Often, when I describe my research project, I am asked how it helps make better mandolins and I pause and remember that one can only make mandolins differently. Whether that difference is "better" or not depends on who is listening, and more importantly, what they are listening for. In this case the person is me, so I will explain in an unapologetically first-person way.

              Here’s what I look for in a mandolin. It is one that:

1) is easy to play

2) provides enough volume that I can focus on expression without having to work too hard

3) has a deep, woody, chunky chop and low notes that can cut through a band or jam or recording

4) has strong resilient highs that have cutting power without being strident or harsh

5) has mids that sizzle and pop, they have a bubbly quality to their tone, like the plop of a drop of water

6) can produce a variety of tones with different techniques and remains pleasant at all volume levels

              You'll see my first criteria has little to do with the build of the instrument and is entirely accomplished in the set-up. Tone is only communicable if the mandolin can deliver it well--then we can concern ourselves with how it is made.

Building Basics

              Basically, a builder can only control the materials and dimensions of a thing. Since the dimensions of traditional F and A mandolins are pretty-well set (more on that at a later date), as are the basic materials (spruce, hardwood, exotics) the material and dimensional choices of traditional carved plate mandolins become choices about mass and stiffness of the materials, even if using non-traditional woods. The space between the parts also matters and is referred to as the air cavity. The builder's control over the air cavity is quite complex but it is an important consideration in addition to the material components.

              Builders can't control how you hear, but our goal is to manage what you hear.  All perception of sound is personal, but the physics of sound apply evenly. The sound we hear can be considered through a few basic measurements: pitch (the fundamental frequency), complexity (the harmonic frequencies), and volume, or loudness. To avoid mistaking air-volume and loudness-volume, I will only refer to air components as “air” or “cavity” or “air cavity”. Any use of “volume” will refer to the perception of loudness.

Tone Shaping Basics

              Some simple rules of thumb from physics can help us understand simplified relationships between mass, stiffness, frequency, volume and air:

• when mass is increased, frequency decreases and vice versa (inverse relationship)

• when stiffness increases, frequency increases and vice versa (direct relationship)

• some frequencies seem louder simply as a result of how our biology works

• the air cavity is affected by its size, the size and location of the soundhole(s) as well as the mass and stiffness of the top and back

• changing the dimension of a piece of wood impacts its mass and stiffness, but not at equal rates depending on many factors

• stiffness increases 8-fold when doubling the height, but only 2-fold when doubling the width

• changes in mass and stiffness in one part can create frequency changes in other parts

• "tone" is a combination one or many simultaneous frequencies

• good mandolin tone is a blessing to those lucky enough to hear it

Philosophy of building.

              From what I've seen and personally experienced mandolin building philosophies are based on a few approaches or guideposts. The first of these is experience and intuition, then deflection, then resonance. There are probably more, but this is how I will frame it while admitting that I use them all.

              As far as intuition, I flex every mandolin I get my hands on. I have built up a storehouse of muscle memory for how top and back plates move with gentle squeezes. Similarly, tapping on an instrument or part can yield valuable information too.  The pop of the initial hit, the length and strength or decay, the frequency of tone all turn into mental guideposts than can lead a person to replicate quality results. I've built some fantastic sounding instruments with no way to explain how except that it seemed to tap and flex well.

              The deflection method applies empiricism to the flex method. You load the part to be measured with a known weight (force) and measure the bend in the piece (deflection) and keep track, looking for trends between good ones vs bad ones. I do this with mandolin tops and backs in a jig that will be explained at a later date.

              The resonance method is often called "tap tuning", though it can be much more than that. Tapping on anything produces a complicated set of frequencies. The idea behind resonance is that components of the instrument are modified during the build until they ring at particular frequencies in particular ways. Most people, but not all, over-simplify when discussing tap tuning, especially with mandolins. Most explanations of tap tuning in casual conversation and internet fora miss crucial details and nuance and make the subject less clear and accessible than it really is.. There are many people, however, especially guitar and violin makers, who are establishing solid methods and data sets that show resonance as a viable way to get good results. I have not seen much resonance data for mandolins and hope to contribute something of value to the field because I believe in it.

              There are other measurable material properties like damping (or "Q"), elasticity (Young's modulus), among others that I am not very qualified to explain here in June, 2024.  I do have a vague sense of their contributions and I expect I will be learning a lot as the years go on and hope to be able to share my experiences throughout. Starting now.

              First to share is what kicked this whole thing off sometime in early Feb/March 2023, around the time I also started reading volume 1 of Gore/Gilet's "Contemporary Acoustic Guitar".

From my notes:

“Goal: I am trying to understand what vibrates where and how, and how that contributes to the overall sound of the instrument.

         - I am trying to discover the best measurements to determine relationships and trends related to tone (not necessarily volume)

         - I am trying to get to a point where I can see a mandolin in the wild, take a couple measurements and be able to analyze the data to see what’s doing what where and what’s its impact, without having to take it home and put it through the paces.

                   - ideal scenario, play a really awesome mandolin in the wild. Get field recordings of taps and some notes and be able to figure the determinant resonant characteristics and what is causing them.

         - I want to reverse engineer the information I get into methods and processes for building to be able to build to a predictable end result “

Initially I wanted to do this with 100 mandolins and I have just about achieved that goal. I realize, as I write this, that last night I encountered an excellent mandolin in the wild, I took some tap recordings of it and now have the ability to say something about how it is built and why it sounds the way it does. I am excited to share more about this in future blogs!

-GB