I spent a few nights and weekends this June designing a 3D-printable banjo ukulele (also called a banjolele, banjo-uke, or ukejojo) which I recently posted on Thingiverse. It was a really satisfying exercise of the rapid iterative design process possible with 3D printers. This project arose from my desire to learn how to play an instrument and a dearth of cheap 3D printable ukuleles (not entirely true— there are some printable stringed instruments, but many are incomplete designs or have lingering design problems that make them impractical).
A conversation with Geoff Wiley of the wonderful Jalopy Theater in Brooklyn, NY introduced me to the banjo ukulele, whose thin, resonant membrane and open-back construction stuck me as very conducive to 3D printing. Several weeks later and after many design discussions with Geoff, I arrived at this design, which uses a thin hexagonal webbing to support a 0.5mm membrane,which produces a nice full tone. Other revisions of the membrane design varied the membrane thickness and webbing structure, both of which impacted tone and volume significantly.
While I have given those early versions away to friends, I was able to compare the frequency spectrums and decay profiles of a classic wooden-bodied ukulele with those of my 3D printed banjo ukulele (printed uke plucks first, classic uke plucks second). It’s obvious to any listener that the two instruments sound different, but these spectra are a useful way to quantify and compare those differences. All four plucks of the printed instrument have frequency bands that extend higher and more densely than those of the classic ukulele. The presence higher frequencies make sense mechanically— the thin, stiff membrane of the printed uke can resonate at higher frequencies than can the porous, thicker wooden chamber of the classic uke. However, both the C and E open strings on the printed uke have wide, early bands that decay quickly while the classic uke has a clearer frequency distribution from the beginning. One final interesting difference is especially pronounced on the open A string pluck: on the printed uke harmonics all start simultaneously, but on the classic uke, higher harmonics don’t start until 3/100ths of a second after the lower harmonics do. I’m guessing this has to do with the geometry of the resonant chamber, but I’m not sure. Though these particular spectrograms are interesting and informative, what I really need is to compare these characteristics to those of a true banjo ukulele (in the works!).
My experience with instrument design is limited, but as a design space, musical instrument design for 3D printing has some exciting potential. In addition to the first-order design implications of the removal of many geometric constraints come the abilities to precisely control bulk material density, vary infill substructure, leverage the laminar orientation of components, and even vary, blend, and laminate the print materials. Exciting possibilities. But first, I should learn a few more chords on the banjo uke.