Detailed Guitar Blueprinting
The basic concept is to get the individual pieces of wood making up the
instrument individually and collectively 'happy' and adjust the bass/treble/brilliance. A few more details play into the work. The pieces of wood possible to easily work in a guitar are the sides, linings or kerfing, braces, top, back, bridge, and saddle. Also the inside of the sound hole(s) (or F holes) can be minimally tweaked. Each little step only makes a small difference. A possible exception is going through the top overall, which can suddenly hit a sweet spot
that's quite pronounced.
A.1. Set up the instrument's frets and fit saddle precisely. Everything needs to be ship shape. Check all the screws and other parts to make sure nothing is amiss. Check/adjust truss rod to the right tension. Because the strings are in the way, we work without the strings on for most of the process. The saddle or archtop bridge fit are especially important.
A.2 Clean up the inside edge of the sound hole, primarily to get the inside edge smooth, without finish ridges and other junk hanging down. This can create an audible improvement. It's not that a lot of air moves by the edge, but that pulsing around the edge can move "noise" into the boundary layer around the instrument's top.
- Body work
B.1 Ribs & kerfing/linings. We work all around the ribs and block, including consideration of any vertical braces. We simultaneously work the kerfing or linings. This can't be done completely perfectly, but does make a difference in conjunction with everything else. We look for paired "hot" and "cold" or "bright" and "dull" spots in the individual pieces of wood and lightly scrap the dull spots to get them to merge with the bright spots. This process of finding the dull spot in a piece of wood that's in the instrument already is behind most of our approach.
B.2 Bracing. Starting with the major braces on the top, we tap along the path of each brace to find high pitch and dull flat pitch, then scrape the bar at the dull flat spot lightly, locating the exact spot by tapping around with the tool to find the most dull spot. Very little wood generally requires removal. Evening out the braces really clears up the sound produced from the
B.3 Top edge adjustment. If the bass is constipated, we assess the bracing at the edges of the top and overall. If clearly overbraced, we consider partially or completely reworking the bracing, but we prefer to leave the major features alone. Usually we find that the braces look, feel, and tap out at being just a little heavy at the edges on the top and sometimes the back. Removal of surprisingly little wood remedies this. In building, I understand some makers will
sand the top in this area, just in from the sides, until the bass comes in. The overall bracing then requires slight retuning.
B.4 Bridge plate. The edges of the bridge plate prove to be somewhat important. This particular aspect varies a great deal from guitar to guitar, but the general principles apply.
B.5 Area tuning. The top and back when tapped will have bright and dull or high
and low pitched areas. We access each open area formed between the braces and slightly scrape the highest pitch domain to bring it into line with the rest. Any major variations within a domain are also adjusted out.
- Bridge and saddle.
C.1 Bridge overall. We tap along and around the bridge, listening for any abrupt
changes in pitch. If feasible, we recontour the bridge to get these worked out.
Then we do what I can to get the wings of the bridge of uniform and balanced.
C.2 Bridge edges. We even up the response of the four edges, two on each wing, tapping the
same and the tap along all the edges reasonably uniform. There's clearly a rapidly approached point of diminishing returns.
C.3 Saddle. The ends of the saddle are usually pretty bright. There's also
typically a bright spot between each string. After stringing, we use a file to even
out the response.
D.1 Soundhole edge. We tap around the soundhole listening for dull and bright
spots. With small pieces of abrasive paper, we take down offending spots a tiny
bit until there's a more uniform response around the soundhole and the inside
edge is smooth.
- Testing and final tweaking.
E.1 String up and listen. We string the instrument up and let it settle in for a couple
of hours. We check each string throughout its range, checking for any dull spots. Usually any dull spots to specific areas of the top or bracing that work differently under tension. We tag these spots with painter's tape. If the treble isn't clean enough or brilliant enough, we also note this.
E.2 Adjustment. We loosen the strings and reach in, making the final adjustments. If more brilliance is needed, we reduce the bracing stiffness a little in the area between the treble side of the bridge and the soundhole and edge. This takes a good deal of judgment for each specific guitar.
F.1 Once everything seems as good as it's going to get, we remove the strings
and polish up the bridge and saddle, clean the guitar, and make sure there's