17 November 2003
In the last email you wrote, “For science olympiad I need to build an instrument that plays two octaves from C3-C5 so I was thinking about making a system where one can play multiple notes on the same string like a guitar. What do you think about that?”
Yes, you are right. The bridges of a canon play the same role as the fingers on the frets of a guitar: the bridges and fingers stop the strings at varying string lengths, which, in turn, produce tones of varying frequencies.
In the figure below, please note that the octave, C4, requires a bridge at length ratio 1/2, and the double octave, C5, requires a bridge at length ratio 1/4. Regarding the latter ratio, make sure that the sound hole is not near the 1/4-length location, otherwise the bridge would drop into the sound hole.
It might be a good idea not to put a sound hole in the soundboard or top of the Little Canon. If you drill small holes into the front and back sides (like on my Harmonic/Melodic Canon and Bass Canon), then you can place the moveable bridges anywhere along the lengths of the strings between the left nut and the stationary bridge.
Finally, I would urge you to consider building a canon with 13 strings. If you leave the first string open (i.e., no bridge) and tune it to C3, this string would act as the first tone or tonic of a 12-tone scale. Then, if you place bridges under the remaining 12 strings, you would have a complete scale that would enable you to play a lot of songs. The advantage here is that you don't have to continuously slide a bunch of bridges around to play a melody. Of course, by sliding the bridges to different locations, you could also tune a lot of new scales and modes of your own creation.
Little Canon Design Considerations