SOME THOUGHTS ON GETTING THE PITCH YOU WANT
It is important for me to have the string pitch in a comfortable singing range,
which has required some trial and error. This will make the difference between a diddley bow that is useable and one that
is simply a curiosity that you build, noodle around with, and then ends up collecting dust in the corner. The
pitch of the open string depends on three things: the mass of the string (i.e., 16 gauge wire will be lower
in pitch than 18 gauge wire at the same tension and length); the length of the string between the bridge and the nut (scrap
of wood) (i.e., for the same mass and tension, a longer vibrating string length will be lower in pitch than a shorter vibrating
string length); and the tension on the string (all other things being equal, a string with more tension will be higher in
pitch than a string with less tension). I have not made a completely systematic investigation of these
three parameters for this instrument, but I can provide some guidance. I will state my preference here
for the meaty sound of a heavy string—thin strings sound thin, and are not to my taste. I
have measured the string length and pitch of the diddley bows I have made, and have interpolated and extrapolated the relationship
of string length (in inches) to pitch for various string materials in the following table:
| 16 Gauge galvanized fence wire | 18 Gauge galvanized fence wire | 0.055" music wire | Broom Wire |
C | 60 inches | 55 inches | 59 inches | 61 inches |
D | 53 | 49.5 | 52.5 | 55 |
E | 47 | 44 | 46.5 | 49 |
F | 45 | 41 | 44.5 | 45 |
G | 40 | 37 | 39.5 | 41 |
A | 35.5 | 33 | 35 | 36.5 |
B | 31.5 | 29.5 | 31 | 32.5 |
C | 30 | 27.5 | 29.5 | 30.5 |
D | 26.5 | 25 | 26.5 | 27.5 |
E | 23.5 | 22 | 23.5 | 24.5 |
F | 22.5 | 20 | 22 | 22.5 |
G | 20 | 18.5 | 19.5 | 20.5 |
These pitches may not be the highest achievable for a given wire and string length, but they are as high as I have
been able to get. It is possible to have the pitch a little lower by reducing the tension slightly, and
in fact, the wire tends to stretch over time, so the pitch drifts down. Therefore I suggest you make the
diddley bow a little higher pitched than you think you will need. Note that the string length is the distance
between the top of the bridge to the nut, NOT the distance between the nails. On the diddley bows I have
built, the string length is typically 3-4 inches shorter than the distance between the nails.
Notice that the string lengths for the 18 gauge wire are shorter than for the 16 gauge wire, the opposite
of what I had expected, since the mass of the 18 gauge wire is less than the 16 gauge wire. The reason
for this appears to be that 18 gauge wire I have used is flimsier than the 16 gauge wire, and does not seem to have the same
tensile strength, so it breaks more easily. For this reason, I have not used 18 gauge wire for recent builds.
Note that the broom wire gives slightly longer string lengths for a given pitch compared to 16 gauge galvanized fence
wire. I do not know if I have a greater tension on the broom wire or if the mass is very slightly less
than the 16 gauge wire.
Once you have made a basic instrument
or two, you may wish to build a diddley bow with a heavy guitar string and a cheap guitar tuning machine. Wound
phosphor bronze strings tend to have good sustain (the notes ring for a long time).