acoustic blueprinting

acous•tic blue•print•ing: The process of refining an instrument for most
efficient operation with minimal noise, sweetest tone, and most open feel.

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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, braces, top, back, and
bridge components. Also the inside of the sound holes (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. Preliminaries:

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, I work without the strings on for most of the process.

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.

B. Body work

B.1 Ribs & kerfing/linings. I learned this general approach from reading
Spears book. I work all around the ribs and block, including consideration of any
vertical braces. I simultaneously work the linings.  This can't be done completely
perfectly, but does make a difference in conjunction with everything else. Spears
has a system linking each rib to a block and getting that balanced out. Works to
some extent on guitars, but isn't nearly as clear.  I'm looking for paired "hot" and
"cold" or "bright" and "dull" spots in the individual pieces of wood and lightly
scraping (very lightly) to get these to merge.  This process of finding the dull spot
in a piece of wood that's in the instrument already is behind most of what I'm

B.2  Bracing.  Starting with the major braces on the top, I'll 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 - can tap around with the tool to find the most dull spot.  Doesn't take
much. Then tap again, find where the dull spot is and scrape.  Pretty soon the
brace is much more even. This really clears up the sound produced from the
unstrung box.  

B.3 Top edge adjustment.  If I've noticed along the way that the bass is
constipated, I'll assess the bracing at the edges of the top and overall.  If a guitar
is completely overbraced, I'll consider completely reworking the bracing, but I'd
rather not.  Usually I'll 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.  Then I'll
go back to the bracing to check it.

B.4 Bridge plate.  The edges of the bridge plate prove to be somewhat important.
If they're really abrupt, I'll bevel them a bit.  I'll also tap along them to get the
response more even.  

B.5 Area tuning.  The top and back when tapped will have bright and dull or high
and low pitched areas.  I'll go over the plate inside and out, tapping.  Using a
scraper inside, I'll gently scrape the interior of the plate in the appropriate domain
(area formed by the intersection of the braces) to bring the tapped pitches more
in line.  I'll also check the domains themselves for evenness, working to correct
the largest imbalances.

C. Bridge and saddle.

C.1  Bridge overall.  I'll tap along and around the bridge, listening for any abrupt
changes in pitch.  If feasible, I'll remove and recontour to get these worked out.  
Then I'll do what I can to get the wings of the bridge of uniform and balanced

C.2 Bridge edges.  I try to get 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, I'll use a file to even
out the response.  

D. Soundhole.

D.1  Soundhole edge.  I'll tap around the soundhole listening for dull and bright
spots. With small pieces of abrasive paper, I'll take down offending spots a tiny
bit until there's a more uniform response around the soundhole and the inside
edge is smooth.

E.  Testing and final tweaking.  

E.1  String up and listen.  I string the instrument up and let it settle in for a couple
of hours.  I'll play up and down the strings, checking for any dull spots.  Usually I
can trace the dull spots to specific areas of the top or bracing that work
differently under tension.  I tag these spots with painter's tape.  If the treble isn't
clean enough or brilliant enough, I'll also note this.

E.2  Adjustment. I'll loosen the strings and reach in, making the final
adjustments.  If more brilliance is needed, I'll 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.   Polishing.  

F.1 Once everything seems as good as it's going to get, I'll remove the strings
and polish up the bridge and saddle, clean the guitar, and make sure there's
nothing amiss.

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