![\"\"](\"http:\/\/leopardshark.com\/music\/wp-content\/uploads\/2012\/02\/ProfessionalMarimba1.png\" "\\"ProfessionalMarimba\\"")
<\/a>An example of a wonderful professional marimba.<\/p><\/div>\n
So… why not build one?\u00a0 Several sites on the web have instructions or tips on construction.\u00a0 Mechanically, a marimba is a straightforward instrument — each note is a specially shaped bar of tonewood (Honduran rosewood, African padauk, etc) suspended above a Helmholtz resonator (tube with one end closed).\u00a0 Two things make it difficult — there are 61 bars and resonators in a 5 octave marimba, and the complex vibration modes of the bar, governed by the unique arch cut from under each bar, makes tuning complex.<\/p>\n
The science behind marimba tuning is amazing, and hopefully Paul will write a long essay on harmonics, longitudinal and torsional vibration modes, and how a fast fourier transform (FFT) can be used to identify harmonics.\u00a0 Folks familiar with pianos, flutes, guitars and clarinets may wonder what the fuss could be about.\u00a0 For an acoustic guitar, the length and tension of the string is all that must be adjusted — the shape and material of the body then provide the rich tone.\u00a0 For an electric guitar, only the length and tension is important, the rest is done with transistors.\u00a0 However for a marimba, every nuance of it’s shape combines to strengthen or dampen the fundamental or a set of harmonics — and because every piece of wood is unique, with wavy grain here and dense sections there, the shape and sound of every bar is unique.\u00a0 Paul’s marimba will certainly be a one-of-a-kind masterpiece.\u00a0 But, we are getting ahead of ourselves.\u00a0 First things first… to build a marimba Paul and I need a good tonewood.<\/p>\n
<\/a>Our first two planks of African Padauk. We probably need 1 more<\/p><\/div>\n
Rosewood is undeniably the best wood for marimbas.\u00a0 We need about between 40 board-feet (maybe less).\u00a0 Rosewood would cost us about about $800.\u00a0 African Padauk, another very nice tonewood is less expensive, is a beautiful red color, and used for good, but not the top-end marimbas.\u00a0 Padauk will cost about $300.\u00a0 Paul is covering “all tropical wood” for the marimba, so he is actively soliciting donations.\u00a0 I’m responsible for everything else — tools, supplies, maple for the frame, aluminum for the resonators, etc.<\/p>\n
Cutting the Wood into Bars (see Progress-O-Meter above: red = bar is cut) Thankfully, Padauk is dense, with tight grain.\u00a0 It is easy to cut, does not often split, and does not burn as easily as purpleheart,\u00a0 However… the sawdust is brilliant red.\u00a0 It floats in the air, it infiltrates everything, it stains our cloths, and it appears to be permanent.\u00a0 The Martian dust has colored our entire planet red.\u00a0 In our first significant cutting session, we were too relaxed with our PPE (personal protective equipment).\u00a0 The rest of the day we blew our nose red.<\/p>\n We will get three bars from this piece of wood.<\/p><\/div>\n Our high-powered dust generator with specialized filter<\/p><\/div>\n The sawdust under our table saw<\/p><\/div>\n The man with the red mask….<\/p><\/div>\n Our Martian dust now blanketing our garage<\/p><\/div>\n The a handful of bars cut, we are ready to begin shaping them<\/p><\/div>\n Shaping the bar (see Progress-O-Meter above: green = shaping completed)<\/strong><\/strong><\/p>\n Because the red sawdust generated by the sander is so insidious at infiltrating everything, and rough-shaping is not practically done in the garage, we build the “Red Box”.\u00a0 A set of plastic tarps set up to enclose the dust.<\/p>\n The Red Box<\/p><\/div>\n Router, Sander, spectromter, and lots of RedBox dust…<\/p><\/div>\n After a “blank” is cut to exacting dimensions an arch must be carved from the bottom. The arch gives the key it’s unique marimba shape.\u00a0 The arch turns the bar into something like a barbell, with a thin middle and heavy ends.\u00a0 For the fundamental (primary tone you hear) the bar will oscillate around a “node”.\u00a0 Nodes are stationary, like the end of a jump rope or bridge for a guitar.\u00a0 The cord suspending the keys will be threaded through a hole drilled through the primary nodes, so the bars can ring long, and without being dampened.<\/p>\n After several attempts, mistakes, some disappointment, and reinvention, we have developed a very efficient set of processes for shaping a bar.\u00a0 A new belt sander with 50 grit has been indispensable, and very quickly permits us to rough-tune the bar.\u00a0 Sometimes, the high-powered sander may be a bit too efficient.\u00a0 After cutting the basic arch with a router and simple jig, the fundamental and first harmonic is about 7 semitones (1\/2 steps) from being in tune.\u00a0 Using the belt sander, we slowly shape the arch, testing frequently with an audio spectrometer to move the fundamental and first harmonic to within 2 semitones (one whole note) away from our target note.\u00a0 Every adjustment to the shape of the bar adjusts several harmonics, so keeping all the ratios between harmonics moving uniformly toward the target is quite difficult.<\/p>\n Paul and his orbital sander<\/p><\/div>\n Mostly protected from the dust<\/p><\/div>\n Preparing to use the router in the RedBox<\/p><\/div>\n We check with the spectrometer frequently while doing basic shaping<\/p><\/div>\n The next step: drilling and oiling the bars<\/strong><\/p>\n After the bars are rough-cut and brought within one whole note of the final pitch, it is time to find the “nodes”, where the hole will be drilled for the string that will eventually suspend the bar above the resonators.<\/p>\n Finding the nodes is done experimentally.\u00a0 Yes, it pains me that we can’t simply calculate their correct position, but not only is the wood grain non-uniform, our shaping is not perfect either.\u00a0 The accepted method for finding the nodes for the fundamental is to sprinkle table salt on the bar and then strike it with the mallet.\u00a0 Since the nodes don’t move as the bar vibrates, the salt will be shaken off everything but the nodes.<\/p>\n The amazing thing, is that it works so well — just salt em up and whack em.\u00a0 Wow.<\/p>\n Salting a test bar made from Jatoba (Brazilian Cherry)<\/p><\/div>\n The nodes identified (and in this case, slightly diagonal)<\/p><\/div>\n For our test bar of Jatoba, the nodes were sightly diagonal, matching the grain and quarter-sawn cut of the wood.\u00a0 However, diagonal is not so bad for marimba keys, since the cord going from largest to smallest key must travel at a slight angle anyway.<\/p>\n After final sanding and then oiling the bar to protect it from drying out, the bar is ready for the final step, tuning.\u00a0 We can’t drill, oil, or final tune the real padauk bars until they are all complete and the exact angle for the cord can be drawn in.\u00a0 So we have only tried this last step on the Jatoba, and will have to wait more than a month before we are are prepared to start final tuning of the marimba bars.<\/p>\n Final tuning of our test bar<\/p><\/div>\n So, we have completed rough shaping for 7 of our 61 keys.\u00a0 Building this masterpiece instrument will take a LOT of work, but we look forward to enjoying it’s sound and the beauty of real wood.<\/p>\n Our first 7 keys. An amazing accomplishment, even though we have 54 more…<\/p><\/div>\n Of course, we have also mixed in some goofy fun while building the marimba.\u00a0 It’s not all power sanders, routers, and FFTs….<\/p>\n Emptying the Martian dust<\/p><\/div>\n <\/p>\n Art can take many forms…<\/p><\/div>\n Whew… a long post, but we have started the project, we will log (nearly) countless hours building something that we both hope will sound magnificent and last a lifetime, maybe more…<\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" Paul and I are building a Marimba.\u00a0 Wow. How did we get here?…\u00a0 Paul enjoys playing marimba and vibes.\u00a0 For a while, we rented a small marimba with synthetic bars.\u00a0 It lived next to the piano at times, or in … Continue reading
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