Some thoughts on mandolin design

For most of the mandolin players, that I come into contact with, the sound that an instrument produces is paramount. As a professional luthier, I always try to build the best constructed and most aesthetically pleasing instrument that I can, but that all counts for very little unless the tone is there too.

We know from the law of conservation of energy, that energy cannot be created or destroyed but is transformed from one type to another. Essentially a mandolin (or any other acoustic instrument for that matter) has to transform the kinetic energy of the musician’s hand into sound energy. That transformation has to be done as efficiently as possible to get the maximum sound out of the instrument.

So you pluck the string, it vibrates (kinetic energy) and you want the maximum amount of this energy transferred into the soundboard.

The job of the bridge is to hold the strings in the correct position relative to the rest of the instrument (for string spacing, action, intonation) and to make the soundboard vibrate.

A bridge needs to be as light as possible, so that the minimum amount of energy is used in moving the bridge itself. However, it has to be strong enough to support the strings and wide enough at its base to be stable. I make my bridges without any metal height adjusters; I feel that any mechanism that cuts the bridge into two parts must interfere with the bridge’s efficiency. Admittedly, I use a removable bone saddle to aid the adjustment of the action, but that saddle is firmly embedded within a deep slot and the bone saddle helps with acoustic impedance matching- metal to bone to ebony to spruce.

My bridge actually looks like a bridge! It makes contact with the soundboard only at the two ends- the central portion is removed; this reduces mass and lessens any restriction of the soundboard’s vibrations. However, by reducing the area of contact, you increase the pressure at the points of contact with the soundboard, which in my opinion, allows the transfer of energy to be more efficient. The feet of the bridge are not in some random position- they rest on the bracing which is designed to support the downward force and to help transmit energy across the soundboard.

The break angle at the bridge is also critical- the greater the angle the greater the downward force. However, if the bridge is pressing down too much on the soundboard, it will choke it- you know yourself, if you press down on the soundboard you will dampen the instrument (a good argument for armrests). The break angle is governed by the angle of the neck relative to the soundboard and is not just a function of the bridge.

The tailpiece should be a rigid anchor for the strings, so that energy is not absorbed by it; my theory is that any of the available energy will follow the path of least resistance and that path should be into the soundboard via the bridge.

The tailpiece must be a minimum length. If the length of the string between the bridge and the tailpiece is too great, you get this part of the string vibrating in sympathy and that’s wasting our precious input energy. You’ll notice that on some mandolins that have the anchor point of the strings close to the tail block, they will have harmonic suppressors fitted to the strings, behind the bridge.

I like to think that the body of the mandolin is like a loud speaker; the soundboard is the equivalent to the paper cone and that the back and sides are the metal chassis. Therefore, the back and sides should be rigid so that they don’t absorb energy from the soundboard. I also like the inner surfaces to be extremely smooth so they act as a reflector.

Having stated some of my design ideas; you should appreciate why I use French polish as my finish of choice. French polish is a very light surface coating and as such will have a minimal damping effect on the soundboard.

Well there’s is my two pennies worth- hope that you found that of interest.