Paul-

DON’T WORRY! It wasn’t actually near-death for dad or me. But for the marimba, it came close. Preparing to line up the new holes for replacement bars, we had a close encounter of the absent-minded kind. We had all the bars in place (or so we thought) and we began sliding a metal rod through the holes of the good bars in order to decide where to drill new holes in the replacements. But each time, the rod came out of the hole tilting the wrong direction. We tried again and again. Yet for every bar, it appeared the hole had been drilled at a reverse angle. A few minutes after this painful realization, we collapsed to regroup and think about solutions, thinking we had just ruined every bar on the entire instrument. Could we drill the other way? Change the post location between bars? All solutions seemed hopeless. Then dad asked a simple question, “Are these naturals or sharps?” At that point I realized the mistake. I had lined the naturals up as though they were sharps, causing the angling of the holes to seem backwards. A quick shift of position led us to the correct arrangement and a disastrous near-death experience was barely averted.

Now that we are confident that we still have bars that will function properly on the instrument, we have begun construction of the rails. These four long wooden pieces span the whole instrument and provide a base on which the bars rest. In order to construct them, we had started to drill holes in stainless steel plates to connect the two halves. We will then drill the same holes in the planks and put bolts through the wood to create eight-foot long rails on which to rest the bars. The pictures will help to explain.

Using the grinder on the stainless steel plates. The table saw is just providing a nice work surface, and is not plugged in

Rounding the corners

I think making sparks is always considered fun

Drilling the rails

The plate connecting it all together

The stainless steel plate. We now need to drill the 3 holes in the other side

Well, although we have made tremendous progress, we are currently in the doldrums of small tasks that seem to last longer than they should, and when completed, appear too insignificant to be considered accomplishments.

Nevertheless, we press on.

The tuning is nearly complete.  55 ruddy bars lay beautifully, but still silently on a table in the front room.  They are splendidly tuned.  I sat in the red box, grinding bits of wood and striking the bar while Paul managed 2 computers and analyzed the sounds.  A spreadsheet of our design calculated each frequency, and a formula we constructed helped us “stretch” the highest notes.

Formulae from our spreadsheet

Human hearing is imperfect in the highest and lowest ranges.  High notes are heard by our brains as flat. It is intriguing. We have to make them sharp (based on the measured frequency) to hear them in tune.  In the low ranges notes must be flattened.

We have 6 bars that we have to re-make.  We have cut them, and now need to drill the string holes and shape them.  Most of them are in a range where the fundamental and the first harmonic are NOT a perfect two octaves apart.  The first time we tried to tune that range our strategy failed.  This time, we will shoot for an octave and a sixth as the harmonic.

The video below shows a properly tuned bar.  Three tones are heard: the second harmonic, the first harmonic, and the fundamental.  The fundamental is so low, the little video camera has trouble picking it up.

A tuned marimba bar: demonstrating the harmonics (the movie takes a while to load…. be patient)

Our next big milestone will be Continue reading →