Luthier's Desk

This is about a guitar named Casper.

Every once in a while, a build happens that teaches many lessons along the way.

This build was inspired in part by the "New England Luthiers"

and was one of many of our guitars played at a Luthiers showcase consert at Club Passim on Sunday Nov. 1st 2015

Casper is a Flat-top acoustic guitar with a design that is optimized to work with a tailpiece.

Its wedged body design is made of spalted myrtle wood and has a cedar top..

      Every stringed instrument I build is a learning experience. Building a flat-top guitar designed to work with a tailpiece seemed a worthy endeavor because of the experimental opportunities it creates. The fact that a tailpiece takes on the tension stresses of the strings diverting it away from the bridge, creates a very different scenario from the more usual fixed bridge. The tailpiece allows the guitar to be strung up before details of the bridge system are finalized. Bridge size, shape, material and position can all be optimized for best tone and transfer of string vibration to the top. Having the opportunity to switch-out bridge configurations and hear the results are crucial for honing-in on the best tone for this guitar.

   Also helping in the experimental process was the adjustable neck joint. Besides being one of the most important advancements in handmade acoustic guitars, the adjustable neck joint made changing bridges and saddles a snap.

This Adjustable neck design is the simplest yet.

   Considering all this ahead of time was helpful in the designing stages of this guitar. First of all, the bracing had to be altered from the usual approach expected for a fixed bridge configuration. I decided to stick with the X brace since I wanted to hold the top into a dome shape. Although the braces will not need to be as beefy as they would for a fixed bridge, I'd still need to counter the down forces of string-break angle at the bridge. With a shallow X brace and thinner finger and tone bar bracing, the hope was to also promote a more responsive top. I was under the assumption that some of the string vibration could get absorbed by termination at the tailpiece. A more responsive top could help compensate for any lack of vibration by supporting and projecting more of the strings vibration at the saddle and bridge. However, the bracing scheme I came up with would be permanent and untested until the guitar is strung-up. Although many builders have their testing methods for creating repeatable success for a bracing scheme ahead of final assembly time, there is no guarantee the tone of the finished instrument will be the best it can be. For this build, with the differences the tailpiece brings, it will be a first-time for many subtle changes that test theory and intuition for my style of guitar making.

The final bridge and break-angle bar.

Once the body had been glued together and the finish finalized, the experiments began. I tried several different configurations of bridge and saddle and was surprised by the variation of tone and projection. I first tried a thin bridge similar to what is used on an arch-top guitar. This produced a very mid-range-y tone. Next, a smallish conventional bridge was still mid-range-y but better. Finally, I made a broader, conventional bridge out of rosewood that tapers thin at the back and wings. This one seemed to tame the mid-range while promoting a transfer of crisp highs and strong low frequencies to the top. Settling on this full-sized bridge, I decided to try one more experiment. I added a break-angle bar behind the saddle that holds the strings to a steeper angle before terminating at the tailpiece. Adding an anchored brake angle to the strings path provides an important variation of the way the string vibration interacts with the top. My guess is that it introduces a small amount of the torque force to the bridge that seems to "activate" the top in a similar way to what would be expected with a fixed bridge. However, with the combination of tailpiece and the response of the top, the "system" seems to deliver a variation from the normal tone and timbre you would expect from a flattop guitar. To my ear, the sound of this guitar is centered at responsiveness of string nuance with a crispness of highs and harmonics. The low frequencies are full and the strong mid-range helps projection considerably.

Reaching this final sound of Casper was possible because of the tailpiece and the adjustable neck joint. The experimenting needed to hone-in on a desirable tone for this particular instrument brought new understanding of not only how acoustic guitar systems work, but how they sound. The surprise was finding out how subtle variations in bridge design can change the sound of the guitar dramatically. It would seem that changing the bridge's size, thickness, weight, etc. is an opportunity to compensate for variations in the top's bracing scheme whether intentional or not. It's a lot easier to change a bridge on the outside of the guitar than the bracing on the inside. And, with the addition of the break-angle bar, the ability to change the timbre of this guitar is simple and easy. Since desirable tone can be very subjective from player to player, it seems a good thing to offer alternatives within the same guitar. With simple adjustments using common Allen wrench tools, the ability to keep Casper at its sweet spot for playability and tone is easy and fast.
Part of what keeps me building stringed instruments are the discoveries along the way. Some help in understanding how to make wood sing. Others help resolve issues I believe need to be addressed to make the guitar "better". Casper is one of those builds where there were many moments of discovery and resolve. I'm getting that much closer in my personal search for the Holy Grail of guitars. Hopefully, by sharing some of my discoveries, I can help a few others get there too.