[Original Post: Mar 17, 2011]

This is a summary of the thread started by John Maw regarding optimal bridge placement. Click here to read the original thread.

1.) It seems each cigar box has a unique "sweet spot" and this is the best place to put the bridge.

2.) You need to know the bridge location before you can figure out your neck length and nut position as this defines your scale length and ultimately where each fret will be located for proper intonation. So, CBG builders should use some kind of test to locate the "sweet spot" of the box they are planing to use so they can first locate where the bridge will be placed before deciding on neck size, nut placement, etc.

3.) The "sweet spot" is generally in the middle of the box, but many other variables can come into play to make the "sweet spot" move to some other place. Things like internal bracing and sound hole placement should ideally be complete before the final "sweet spot" test as doing them afterwords can move the "sweet spot".

{ I also assume that the neck attachment method may also be a factor (neck-thru verses bolt-on, and whether the bolt-on relies on an external heel, or heavy internal bracing. Pretty paper labels, the addition of pickup controls (cable jack, switches, volume and tone pots) and other decorative items will likely also adversely affect the "sweet spot" and the optimal bridge location. For this reason, a "clean/plain" design with pickup controls on the side (and maybe sound holes on the sides) of the cigar box may prove better than placing all that "junk" on the soundboard.}

4.) Putting the bridge in the middle of the box doesn't give you much space to pick or strum the finished guitar. For this reason, the bridge is pushed back toward the tail end of the box (usually 60% to 75% of the way across the box). This is the likely the original reasoning behind the often cited CBG builder's rule-of-thumb: "Place the bridge about 2/3s to 3/4s across the box (down from the point of neck attachment)."

5.) Should have a way to test the "sweet spot" of a box.

Method 1: Use a tuning fork.  Maybe you can use additional tuning forks (each tuned to a different note) to test the frequency response of the box over a wider range of frequencies. Marking the various sweet spots on the sound board and then figuring an "average sweet spot" and placing your bridge there.

Method 2: Build a "test jig" composed of a head and neck assembly (with machine tuner(s), string(s), nut and tail piece already in place) that can be easily attached to a box. (I'd like to see some pictures of one of these.) It can (should?) be fretless. Use it along with a movable bridge to find the "sweet spot", then plan your scale length, neck length, nut placement and fret spacing based on that "sweet spot" as the bridge location.

6.) Try to increase the break angle of the strings over the bridge by increasing the bridge height. This will put more force on the bridge and theoretically make the box sound louder. But, doing this will also raise the strings off the neck/fretboard resulting in "high action", which is likely something you don't want (unless you are a slide player). So, to compensate for the high bridge design your neck so it tilts back a few degrees so the "action" (string height off the fretboard) will be lower.

7.) Other tips for building a better CBG:

• Choose a large (length, width and depth) wooden cigar box with a thin lid top (soundboard). The thin top will allow your soundboard to vibrate more readily.
• Often times the bottom side of the cigar box will be thinner and so will make a better soundboard than the top side.
• Choose a box without paper artwork on the soundboard as this just will dampen the sound.
• Consider rebuilding the box so that all the mating surfaces are tight and well glued.
• Consider removing the top (or bottom, which ever will be your soundboard) and replace it with either a thin (1/8") veneer or with real sound wood. With sound wood, you will likely need an electric planer (a power tool) to plane it down to such a thin size and then maybe some light bracing to strengthen the soundboard, the way luthiers do when building real guitars.
• Consider building with a home made box rather than a cigar box, using more of the techniques used by professional luthiers when they make their sound boxes.
• Consider building with a metal resonator using a thin metal resonator cone such as those made by Old Lowe.
• Consider adding a magnetic or piezo pickup and go electric.

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