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 mandolin are
the ribs, linings, bars, top, back, and bridge components. Also the F holes and F hole
edges.   Keep in mind that each little step only makes a quite small difference. A possible
exception is going the top plate which can suddenly hit a sweet spot that's quite

A. Preliminaries:

A.1. Set up the instrument's frets and fit bridge precisely.  Everything needs to be ship
shape. Check all the screws, make sure nothing is amiss.  Check/adjust truss rod to the
right tension.   The bridge is kept off too allow an easier first pass on the body.

A.2 Clean up the inside edges of the F holes (or other ports), primarily to get the inside
edges 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. Bridge preliminaries – a crucial step.  Even if you don't do anything else, the bridge is
worth messing with. If the bridge isn't very good to begin with this step isn't going to
make it suddenly become a good bridge.  Might want to replace it.

B.1 Base. Past fit, the wings outboard of the posts are pretty important. Many of these
have a big lump towards the end. I take a compass, running the point under the bottom
end and the lead along the side to mark a line indicating uniform thickness, then remove
irregularities, making the wings pretty close to uniform thickness. Then I tap along the
wings with a pick, listening for a uniform pitch. Dull sounding spots I reduce a little
more. This usually results in a gentle rollover at the end. Once that's done, I polish up the
wood and cut a bevel on the sharp edge of each wing. Keep the tapped response even
across the base, too. This really plays into the ease of getting things working later. If
you're interesting, look at tuning marimba bars. There
are other things that can be done, but they look a little funny.

B.2 Saddle. This piece of wood really influences the clarity of the instrument
substantially.  I use the tap pitch to contour the top and bottom of the piece. Then later
work the four edges of the ends, by the posts, like a marimba bar. The typical pattern:

B.2.a The longitudinal line of the top surface gets rounded over slightly, the amount
depending on the tap, getting a pretty even pitch.  The only significant amount of wood
removal is at the ends.

B.2.b Several areas of transition all the top surface generally prove a bit dead. These spots
are where the thick ends go thin, and then the jogs in the top edge. I use a half-round fine
Grobet file.

B.2.c The bottom of the saddle is often a bit dead in the middle part. Just scraping this
down a tiny bit helps.

The sides can be worked as well, but looks funny.

B.2.d The edges fore & aft of the post holes are very important, I think that's because
they're close to the posts, which transmit sound to and from the base and the rest of the
instrument. I get these to all tap about the same. Doesn't take much. This is a key
adjustment I return to several times.

C. Pre-setup body work

C.1 Ribs & kerfing/linings. I learned this from reading Deena Spears book. http://www. I work on each segment of the ribs. 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 on
mandolins, too.

On an A model, I tap at the end block to one side of the button and then at the widest part
of the instrument, about the middle of the rib. Normally the block will tap higher. If the
block taps lower, then I make a light scrape along that side of the end block. Use a
scraper on the end of a bent rod. You'll need a good number of these things. Usually a
small amount (very very little) scraping will drop the tapped pitch at the block. Then I'll
tap along the rib to find the dull lower pitched spots. I'll lightly tap with a scraper inside
the rib until I find the center of the dull spot, then scrape that a little bit, and test the
kerfing adjacent to that spot. Usually they'll be minor dull spots offset from the main one.
I'll tap again and find the next spot that's not happy.  And move on to the other side.   On
an F model, there are 3 ribs to work, and I'll also test along the complex block at the
neck. Eventually all this will work out to have no big dead spots around the ribs, just light
variations. I can hear the tapped sound of the unstrung body clear up a bit.

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 doing.

C.2 Tone bars or X bracing.

This will get refined, of course, once there's pressure on the top. Same basic principle.
Tap along the path of the bar to find high pitch and dull flat pitch. 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 bar is
much more even.

C.3 First tone adjustments.

C.3.a Tone - The area between the treble foot of the bridge towards the fingerboard is
important. Tap around that area of the top, listening for dull spots. Very lightly scrape (or
sand) the inside of the top at that spot. A few passes and that area will be more even.
Tone will end up more open and "ah" in character.

C.3.b Balance - Tap the region between the upper eye of the treble F hole and the rim
along the grain mostly. There's often a dull spot. Scrape lightly - and I do mean lightly,
this isn't really about removing any mass to speak of - to get rid of that dull spot mostly.
A little bit is OK for this part. Just don't want a big dead zone.

C.3.c Brilliance. Wing of the treble F hole - if there's a small dead or dull spot on this
wing or back along the edge to the notch, then gently scrape under that dull spot. A
substantial dull spot indicates a lifeless top end is likely.

C.3.d Sequencing top and back. This is a bit more difficult. Tap all around the whole top,
listening for the brighest, highest pitch spot. Lightly scrape under that spot. Repeat until
the top is pretty even. The character of the response should change a lot, often rather
suddenly sounding more open. Do the same for the back. A good example of this was a
Weber Yellowstone I went through. The top and back were so close to being dead on -
very impressive work. And with the most tiny adjustment the instrument just lit up!

You'll note that I require scraping access to the entire interior. I have a wide range of
scrapers on rods bent to do various things. I also have a bent wire scraper that
incorporates a guide to show exactly where I'm scraping. After I go through the
instrument this way, I start over on the ribs and run through the whole sequence again.
Sometimes things change a bit.  Now string up the instrument, see what you're moving

D. Refining the adjustments.  Start with the instrument strung up. Usually sounds and
responds a bit differently than before! I let the instrument settle for a few hours or days if
possible to get used to being strung up.

D.1 Ribs - Check the ribs as described above. Usually they'll be a few changes.
D.2 Check the bars as described above

D.3 Tap around the area between treble foot of bridge up to along side fingerboard. Listen
for any dull spots. These are usually more stable now, and can be gradually reduced with
very light scraping. Can clean up the tone quite a bit. If the tone seems as if it could be or
should be a little more bell-like, check from treble side of bridge towards tailpiece.

D.4 Listen to bass/treble balance. Often still too much treble emphasis. Find a dull spot up
from the treble F hole. Almost always if the instrument is too trebly that spot is present.
May take a bit more vigorous scraping. Still not much at all. Just dust. Try until the
balance sets right. Usually this is a fairly sudden transition.

D.5 Listen for clarity of upper harmonics. Usually just a little lacking. Find dull spots
outboard of treble F hole and lightly (lightly!) scrape under these! Doesn't take much.
Usually one spot about 1" from the wingtip. This makes a tremendous difference in
perception of lively response, projection, excitement.

D.6 go through the top and back as described above. This regularly gives a big boost in
response and apparent volume.

D.7 Check ribs and bars, repeat above as required for stability of adjustments.

D.8 Final work on bridge

D.8.a The wings out from the bridge - tap along them listening for a dull spot. Lightly
scrape until no dull spot. Buff.

D.8.b Tap each of the four junctions of top and side of the wings. One will be higher
pitch. Lightly scrape that corner/edge. Repeat until they are all about the same in pitch.

D.8.c Tap along top of saddle, checking for dull spots. Scrape dull spots.

D.8.d Tap the four edge/corners by the post holes and adjust as is D.8.b.

D.8.e Go back and check the bridge base wings again. This may take a few go arounds.

D.9 Tap around edges of F holes for dull spots. Light pass (very very light) with a file
will remove dull spots. Once these all balance out, polish inner edge with fine abrasive
paper and recheck.

D.10 Ears of the Angels step. This one is a bit odd. Tap the back along the path of the
bars. Often they'll be a dull spot. Find the spot on the bars opposite that dull spot and give
it a light scrape. Usually a small dead spot can be found on the bar there. Makes a subtle
but surprisingly difference.

E. Repeat all of the above from the beginning until the instrument is stable and sounds
good. Stain the inside edge of the F holes if you like.

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