upgrading an arcthop

April 7, 2017

Recently a client from Hawaii sent me an arch-top guitar of his from a Chinese manufacturer. It was a pretty nice instrument, it had a nice top, some really nice maple back and sides, solid ebony and I could tell it had some real potential. But tonally it was very unbalanced, hollow sounding, lacked focus and dynamic range. It just wasn’t a very pretty musical sounding instrument. It sounded like so many manufactured arch top guitars sound… thin and tiny.

blog The task at hand was to

–improve the tone of the instrument

-Replace the stock pickup system with a floating Bartolini

-Pretty up the guitar with my own custom tail piece cap and pick guard

-Full fret job

– install a bone nut and set up to my clients specs. (very low action, light touch)

– Create a re-engineered bridge to improve the activation of the top

In this post I will just speak a bit about my thoughts and approach behind the modification of the bridge in order to improve the tone of an instrument.

I’ve learned from bowed instruments that there is a tremendous amount of movement in the bridge of an arched top instrument. That movement is not the same across the bridge. From the lower strings to the higher strings that movement changes in type, speed and duration and creates twisting and some erratic behavior. All of this translates to a lot of wasted energy. Now, in the a bowed instrument, with the continuous application of a driver (the bow) this doesn’t have the same negative effect as on a plucked instrument. A bowed instrument is getting continuous energy driven into the bridge. But, when you pluck the string of a guitar that energy immediately starts to dissipate. So what we want on a guitar is to get as much of that kinetic energy into the top and bracing as possible. So, in my mind, movement in the bridge is a bad thing.

On this particularly arch top (and many that I see being manufactured) the bridge was originally very narrow and tall. I guess you could say this is the “traditional” style arch top guitar bridge since this is the same bridge that Gibson was using (and still uses) on their arch-tops. So the first thing I wanted to do – to answer the problem of energy killing movement – was to widen the footprint of the bridge and use my wide diameter handmade thumbwheels to add stability to the system. This helps to solidify the bridge structure to prevent some of that movement.

The second issue is mass. I think there is a fine line to walk between too much or too little mass in instruments. energy travels fastest through solid objects. This is why the denser materials like ebony make good bridges. because the molecules of Ebony are packed together much tighter then, say, sprue. But, heavier objects also require more energy to vibrate than lighter objects.

So, my theory – which I have developed over the years by experience and also talking with some great arch top builders – is that while we want the material we use for the bridge to be dense, we don’t necessarily want it to be a solid heavy mass. How do I achieve a wider footprint, with added material, but at the same time reduce the overall mass of the object? This is where I depart from conventional wisdom.

I hallow the bridge out. Using a series of holes in the underside of the bridge and saddle located in ways that allow me to maintain the strength of the saddle and contact with the top, I remove as much material as I can.

This particular bridge started with a weight of 34grams. I added material and brought that up to 40 grams. When I was finished I was at 16 grams.

blog After intonation each string on the saddle piece the bridge was finished.

After the bridge I added the Bartolini pickup with my own wiring harness. I love these floating pickups for arch-tops. They don’t add much to the acoustic tone of the guitar which is why use them on my instruments as a default. But combined with a good capacitor they do have a wonderful smoky warm tint to them.

The results were significant. The instrument sounded much fuller. It had a much more balanced and dynamic tone, and felt much more responsive. There was still a healthy brightness in the full acoustic range but now it wasn’t tin sounding and hallow. Aside from the more subjective colorful characteristic, it also empirically activated the top and back better. I couldn’t feel the back vibrating much when it came into my shop. When it left it was vibrating noticeably more.

I’ve been asked to re-engineer the bridge on 6 different arch-tops by various clients to date (including a second instrument from this same client in Hawaii as he was so impressed with the difference). Every time the result is the same.

I would be lying if I claimed I understood exactly what is happening on a physics level. I don’t. I’m constantly learning more and just haven’t gotten to the point yet where I have a quantifiable/empirical explanation. But, from a theoretical basis, what I believe is happening is two fold.

-The increased stability of the bridge, through a wider footprint and my larger more stable thumbwheels, means that less energy is wasted in the extracurricular movement of mass.

-The strategic removal of weight in the bridge while still providing full contact with the top, allows for the kinetic energy of string movement to activate the system of the bridge, top and braces more freely.

Here is the finished product (sans the pickup which I hadn’t installed yet when I took this photo). In addition to eh bridge, I also created a custom pick guard and tail piece with gold leaf inlay accents in the style of my church model.

In conclusion… Many manufactured arch-tops are not properly voiced. They sound hallow and thin but unlike the flat top guitar where the core of tone is generated in the internal structure of the instrument and the bridge is a fixed component, an arch top guitars tone can be easily improved by modifying the bridge and the tailpiece (length of behind the bridge string and down work string pressure angle) in order to work better with the curvature and bracing design.

Thanks for reading!

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