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Permalink Reply by Russ Dugger on August 6, 2013 at 5:25am

This is seriously clever-as-sin! I love the look of it. And ditto on the headstock, really great look.

Congrats on a successful one-day-build!

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Permalink Reply by Daddy D on August 6, 2013 at 6:14pm

I love the headstock and the way you just screwed an 1 1/2 piece on top of a 1 by 1 for the neck and fret board. Use Oily's fork tailpiece and that thing is perfect. Make sure your bridge is made of something hard too. That will help the sound.

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Permalink Reply by Shannon on August 11, 2013 at 4:34am

Thanks for the replies! I bonded on 7 more brass rod frets.  It totally works.  I used a loctite brand gel superglue.  It gives you a little "work time" to accurately place the fret, then a little pressure and it starts to bond.

Below is a pic from installing the new frets.  The glue is not cleaned up yet in this pic and the ends aren't dressed at all.  I wanted to make sure the fret positioning was good before putting the the work into it so I restrung it as soon as the glue was dry. Frets positioning good so far -- in tune up to the last (7th) fret. I realize that real frets aren't expensive or hard to install but I'm trying to keep this one free of luthier materials. If only I could figure out an easy DIY solution for the tuners...

Still trying to figure out a good place for a sound hole or holes.  Notionally I think I should put it in a sonically "dead" part of the soundboard, but the whole front is ringing pretty evenly. The "bridge" is just chunk of 1/4" mystery wood with some slots cut in it. Other than using a hard material, what else should I consider in the bridge design? I don't know whether it should look like a Banjo style bridge or or a guitar style bridge.

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Permalink Reply by Ron "Oily" Sprague on August 11, 2013 at 5:10am

Shannon,

Those brass rod frets look great. Great 1-day build, too. Of course, now it's gone into multiple days, due to tweaks. This is normal. Re sound hole: put one in the upper shoulder, the corner nearest the neck, and nearest your chest as you hold it right handed. Not right in the corner, but centered in that general area. Make it no more than about the diameter of a US quarter. Re bridge material and shape: your current bridge is also your saddle. Experiment with a relatively wide piece of hardwood, say about 1" wide by 2-1/2" long by 1/8" thick (oak, rosewood, mahogany, or whatever you have lying around), and a piece of bone for a saddle. You can get a decent pice of bone from PetSmart for under $5, or ask a local grocery store butcher if he'll slice you a long bone longitudinally. Cut a straight relatively thin bone sliver, maybe 1/8" thick by about 2" long and 5/16" wide. Sand it up, then put in a 1/6" slot cut into your hardwood bridge. You could also use some brass rod for a saddle.

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Permalink Reply by Shannon on August 11, 2013 at 6:20am

Ron-  

Thanks much for the compliment and the tips.  I'm super surprised at how small of a sound hole you are recommending -- the hole on my fancy soprano ukulele is about 1-1/2" dia.  Is there a rule of thumb about cavity volume to sound hole diameter ratio?  I'll follow your advise, though.  One can always make an existing hole bigger but not smaller.  I was originally wanting to make a 1" x 2-1/2" "slot" under the strings close to the neck.  Because of the materials I started with, and the way I built the instrument, the string height above the soundboard is only ~1/4". The slot would give me a little more pickin' space.  I can go with a taller bridge/saddle but the action is super sweet right now

I'm going to play with the bridge/saddle design today. I have some old circuit board I can scavenge for the saddle until I get my hands on some bone.  The circuit board material is resin impregnated glass cloth and should be pretty stiff and dense.

Thanks again!

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Permalink Reply by Ron "Oily" Sprague on August 11, 2013 at 12:39pm

Shannon,

There's some calculations that can be done for "optimal" soundhole size, on the basis that a guitar approximates a Helmholtz resonator. There are a number of threads from late 2011 here on CBN that go into the theory and calculations, plus an Excel spreadsheet I did to plug in box sizes (for box air volume), string length, and tuning; in addition to that, another CBN member and I collaborated on an experiment in sound hole size variation and sound pressure (dB), that essentially corroborated the optimal calculations. Reason I said about the size of a quarter is that many CBG players find their initial builds tinny or banjoey sounding, and are looking for a deeper, warmer sound. Soundhole size relates directly to frequency, as well as volume; there's a point at which increasing the soundhole size actually doesn't help. Smaller soundhole = bass frequency emphasis, larger = treble frequency emphasis. A standard acoustic git has a soundhole of approximately 3-1/4" diameter, which combined with thin rigid walls, and specially tuned top bracing, allows for a balanced frequency response for 6-stringers, and has apretty significant internal volume. A standard uke has a soundhole that's maybe 2 to 2-1/4" diameter, with about half the internal air volume of a standard git. Do you see where I'm headed with this? A cigar box like the type you've built has about half the internal air volume of a standard uke, so your soundhole should be...uh huh. The Kaman Corporation, which builds Ovation Guitars, did extensive research on soundhole size and placement versus body volume and top thickness, which resulted in the multi-hole soundhole pattern found on their Elite line (which also helps reduce feedback from the internal bridge piezo). There are several builds like that around here, with maybe a 1" hole in the center, and 3 1/4" holes equally spaced around that. And yet, every once in awhile, someone will build a loud box that sounds great acoustically with no soundhole at all. Go figure. It's all about transferring string vibration directly to the top as much as possible. I have a six string Las Cabrillas that Dan Sleep made for me that has no soundhole, but is surprisingly loud; what it does have, is a 1/8" slit below the neck, where I suspect Dan was giving himself space for neck angle. I have used a dB meter on this box, and can confidently assert that most of the sound produced is coming from there. It's a pretty loud box for its size.

You could do a sound slot, which is what I think you're suggesting, instead of a round hole; there are a few builds I've seen here like that, and Godin Guitars uses that idea: they typically put 3 1/4" wide rounded slots in the upper bout or shoulder. Try to make the total slot area no large than the area of a, say, 1-1/2" diameter round hole. It's also a kewl look.

My personal opinion is that there can be such a thing as too many sound holes, too.

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Permalink Reply by Shannon on August 11, 2013 at 2:43pm

Ron-

Once again, thanks for the awesome response and tips. This is really interesting stuff.  I actually just spend all afternoon researching the old soundhole posts and various Helmholtz resonator topics around the web.  I built a spreadsheet to calculate that "optimal" soundhole diameter from my internal box dimensions (also accounting for the volume taken by the neck).  I included calculations for multiple holes and backed out the closest fractional drill sizes for the multiple holes, too.  My box is 8 x 7.85 x 0.9375" and the neck takes up .75 x .75. x 8" for a net volume of  59.06 in^3.  The calculation gives me an optimal soundhole diameter of 1.17" (~1.09 in^2).  

I ended up geeking up a prototype for a circuit board bridge/saddle.  It's just an inverted T of two circuit board segments bonded together.  The acoustic transmission is pretty awesome! I'd say it's about 3/4 as loud as my standard uke now -- without any sound hole(s) -- sustain is great. The sound is actually a little muddy, rather than tinny. I have a feeling that thinning out the 1/8" soundboard some will help clarify the highs.

Cheers!

Shannon

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Permalink Reply by Ron "Oily" Sprague on August 11, 2013 at 8:10pm

There ya go: tweaks upon tweaks for us guitar geeks. 1.17" = just slightly larger than a US quarter, so you should be good. Aren't you glad you took the time to research and run the calcs? Now, you too can have other people tell you 1) you're crazy, 2) it doesn't matter, it's just a stick and a box , and / or 3) you're crazy. People tell me I'm full of it all the time when I tell em this stuff, mainly because they don't have the math, or would rather figure it out empirically.

I like your circuit board T saddle / bridge combo. Since you haven't cut a sound hole yet, the sustain and volume you're now getting are primarily due to driving that soundboard boxtop more properly (the increased volume) and the neck-through design (the sustain). The muddy tone will clear when you open up the soundhole; you gotta give those bass frequencies some place to resonate through. Next step would be maybe thinning the top. Funny how this "oh, it's just a stick and a box" leads down all sorts of interesting tonal byways...

For an interesting alternative at volume increase, do a 1-hour Uncle Crow build. His works because the neck is attached to the outside of the box bottom, causing the neck to act like a huge bridge about 2/3 to 3/4 the length of the box. This is pretty efficient at transferring string vibrations that often get "lost" in the neck on conventional gits. It really helps drive the air inside the box, the same way a mountain dulcimer is built. And of course, now you know how to calculate an optimal soundhole size :-).

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Permalink Reply by Bluesheart on August 23, 2013 at 4:14am

Great job and interesting reading in these posts!  I really admire the knowledge of folk like Oily and The Kid and appreciate their willingness to share it!

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