Just about done with this project and starting a new one. If anyone's interested, here's a link to a youtube vid of the (near final) project:
If you're listening carefully there's a bad buzzing in the strings that I couldn't isolate until yesterday - it was with the bridge having slots too widely cut. That's being fixed now.
Been tinkering away at a slower pace on the instrument, but this weekend my gf is away and I'm planning to make a lot of progress on the next steps. That will include major sanding, installing the tuning machines and finalizing a tailpiece. Just bought a used scroll saw from craigslist for the occasion.
I debated whether to use a magnetic pickup or piezos. I have chosen piezo disks adhered to the underside of the top lid for pickups, mainly because I bought me some weed trimmer string of the thicker variety (.130", .105" and .95"). Magnetic pickups would need strings with metal content, I think.
I picked up some corian samples for the bridge and nut. I get the impression that the bridge should have as little mass as possible so that the lid of the cigar box receives all the possible vibrations from the strings. Is that true?
If so, should I thin out the bridge as much as possible (with only enough "feet" to keep it standing upright)?
You can also do the bridge like a U shape so only two parts touch the lid. That'll take away mass.
Find the bottle cap piezo tut if you can (you tube has it) maybe here too.
Basically you put some hot glue in bottle cap, push piezo down in it. Top it off with glue. The metal cap can rest on the lid (I put mine on the neck and the lid comes down tight on it). Works great.
*\the glue encasement gets rid of rubbing noises from your arm/box
Murdoc_420, thanks for the tip on the bottlecap piezo. I'd never heard of that. I'm curious how it's different from hot gluing a piezo disk onto the underside of the lid. Does the bottle cap afford more isolation from surface noise?
I did end up fashioning a bridge out of some oak corner molding and it seems to work.I have a working model now of my instrument.
Overall, I'm finding some of the subtler aspects of the project and how they translate into a usable musical instrument.
1) I bought rolls of Gatorline Magnum trimmer line for the strings. Guages .130, .105 and .095. I thought the existence of a reinforced inner core might solve the problem of prolonged stretching. While I do think these trimmer lines are high quality, I'm not sure if it was really necessary. I've eliminated the .130 guage and used the .105 for the low E string and picked up some more standard .080 for the D string. The E is a bit floppy, but I can work with it. Amplified, they sound similar to the Kala U-Bass sound.
I did try stringing a steel commercial bass string onto the box using hand tension and it was very noticably louder. I was going to abandon the trimmer line in favor of commercial strings when I found an insurmountable problem - even though I had set up the scale to be 32" (a compromise between the standard 34" and my 30" short scale jazz bass), the length from the bridge to the tailpiece was longer than any commerical string could handle, even long scale. If I want to go that route, I'll have to modify the whole tailpiece.
2) I've only double-sided-taped the dual piezos into the inside of the box so far and there's a lot of handling/surface noise. The hot-gluing and possible the bottle-cap arrangement Murdoc_420 monetioned may be the way to fix that.
3) I noticed the open A string hardly lacks the fundamental frequency - it sounds like I'm playing a 12th fret harmonic when I pluck it. Is that a property of piezo placement or is it something so inherent in the box design that I won't be able to overcome it?
4) If I make another CBB, I'm going to make it so I can open the box even while there it's strung up. Kinda a gotcha there. I'll also try to make a very slight angle on the neck in order to allow for a higher bridge, and possibly more string tension. Oh yeah, and I'll measure the string length to allow for commercial bass strings (I'm particularly hoping to use Fender 9120 tape-wound strings to emmulate an upright).
This continues to be a fun adventure in music/construction. I'm thinking my next project will be an upright fixed neck 4-string built atop an overturned 5 gallon galvanized garbage can.