Building the Marimba - page 5

Jeffrey La Favre -

Simple jig used for brazing tubes with one miter. This jig was also used to braze the 3rd miter on resonators C#2 and D#2. The jig is made from two pieces of 2 x 6 framing lumber, each with a 4 inch section of 2 x 2 angle iron attached at one end. A piece of aluminum 2 x 2 angle was slipped under the open end of each tube and the 2 x 6s were shimmed as required to make the mitered ends align. Photo also shows the MAPP gas torch used for brazing. A brazing rod can be seen on the left side of the photo.

Bass resonators for natural bars. If you look closely, you will see that the F2 resonator angle does not match the other L-shaped resonators. The F2 was the second resonator I brazed and I made an error in the joint alignment. Nevertheless, it is still serviceable. The C2 and D2 resonators are 4 inch (OD) tubing, the E2, F2 and G2 resonators are 3.5 inch tubing and the A2 and B2 resonators are 3 inch tubing. The E2 resonator joints are finished (coated with epoxy and painted with chrome paint). The F2 resonator joints are coated with epoxy. The remaining resonators have only the brazing material at the joints, not filed down yet.

Bass resonators for sharp bars. C#2 and D#2 are 4 inch tubing, F#2 and G#2 are 3.5 inch tubing (A#2 resonator is straight because the sharp rank of bars resides at a higher level than the naturals, thus allowing enough clearance for the A#2 to be fabricated as a straight tube).

Photo below is C#2 resonator from another viewpoint. The C#2 and D#2 resonators were fabricated with three miters, which was required to move them to the side, thus allowing room for the F#2 and G#2 resonators (see model on page 4).

Photo below: attaching the natural bass resonators to the instrument. The bass subassembly is raised so that holes can be drilled into the top of the tubes (the rails are already drilled and are used as pilot holes for drilling the tubes). Each rail in the bass section is drilled with two holes per resonator as can be seen in the photo. At this stage only the top hole has a bolt, allowing the resonators to swing in a left-right direction. Shims will be placed between the tubes and the entire subassembly will be tied down. Then the bottom series of holes will be drilled into the tubes. Extra vertical length was added to the bass resonators to allow for alignment of the horizontal sections. The resonators still need to be trimmed at top to establish proper height above the rails.

If the bass resonators were only mounted at the rails, they would flex the rails and move away from a 90 degree vertical position due to the offset weight of the horizontal sections. In order to prevent this, a mounting bracket will be attached to the horizontal sections and will be connected to the bottom horizontal member of the frame.

Look at the lengths of the horizontal sections of the bass resonators (they are from right to left: C, D, E, F, G). You should notice that the difference in length between E and F is about half that of the difference in length between the other adjacent resonators. In order to understand the reason behind this, we need to look at the musical scale.

In the standard octave (C, D, E, F, G, A, B), tuned with equal temperament, the frequency ratio between adjacent natural notes is a tone or a semitone, depending on the note pair. The ratios for C and D, D and E, F and G, G and A, A and B are tones while the ratios for E and F, B and C are semitones (half the frequency difference of the others). That is why the length difference between the E and F resonators is about half that of the others. It is also the reason why there is no E# and B# in the chromatic scale (and why there are gaps in the sharp rank of marimba bars, or the black keys on a piano). For example, the frequency ratio for C and C# is a semitone as is the ratio for E and F. Therefore, there cannot be an E# since it would be a semitone above E, just as F is a semitone above E.

In my younger and ignorant days (about 5 years ago) I was stumped by this fact when I was building a harp from a kit for Katy . When it came time to tune the harp, using an electronic tuner, I noticed that there was no E# or B# on the tuner. I told Adrienne (my wife) that there was something wrong with the tuner. When I was tuning up a string, the tuner was indicating E, then just jumped past E# to F! I guess I have come a long way since then. Making musical instruments has allowed me to appreciate music in a new way. Whatever I learned in music class in Junior High and the few weeks of private piano lessons must be locked away and inaccessible to my active memory!

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