The basic layout

 

To make the soprano marimba I used a double frame.  The outer frame carries the legs whilst the inner frame makes up the rails that support the keys.  The hinge that joins them allows the rails to be lifted so the resonator rack can be dropped in from above.    The resonators are held about 2cm below the keys and are made from 5cm diameter plumbing tube.  These are plugged with plastic discs cut from a food preparation board.  The plugs close the tubes so that these are all one quarter length of the wavelength for each note, the details of which are given in the dimensions table provided on another page of this website.  

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The keys are strung together by one cord that runs along the rails supported by vine hooks.  A second cord utilises the same vine hooks and forms a tight supporting loop that acts like a trampoline for the notes as they are struck.  I could have avoided using this second cord if I had not screwed the vine hooks in so deeply.  However, with these being set so deep the keys would have bounced on the rails without the trampoline cord to prevent this.  I chose to screw the vine hooks in less deeply when I later made the tenor marimba, avoiding the need for the second cord.

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The keys are made from karagatch, a hard wood in the elm family which is widely available in Kazakahstan.  These 50 x 5 x 5 cm blocks are made of well seasoned, well dried, high quality wood with very few knots.  These blocks, cut in regularly sizes, are intended for turning on a lathe to make bannister rails.

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The keys range from 13cm to 30cm in length, each being 1 cm longer than its higher neighbour, and play notes from C6 down to C4.  The two octaves include F# and so can play in the keys of C and G.  

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Cutting the keys

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The keys were cut and drilled to allocate then to their respective noted prior to tuning them.  They were also trim routed and sanded to smooth any angles.  The keys were not stained, although this is something I will consider in future builds.  The keys were marked on the side with a centre line, and with the 22.5% line going through the support holes.  Additional guide lines were drawn on either side of the centre line at 30%, 35% and 40% from the ends to help make decisions on the routing regime.  

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The first cut of the router was made between the 25% lines and were cut with a rounded bit set at 6mm.  After recording and analysing the frequency with Audacity, the second cut was made at about 10-12mm between the 35% lines or the 40% lines depending on how much of a change in the frequency was required.  Once within 10 to 20 Hertz of the intended fundamental, a hand file was used to remove a trough of wood from the centre of the key to further lower the note.  The note would then finally be smoothed off with sand paper to bring the note to within one Hertz of the fundamental.

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In later tunings I moved away from using Audacity as it proved harder and harder to analyse the data for progressively lower notes.  Instead I used a sound generator downloaded onto my iPad to generate the sound of the intended fundamental.  I then tuned the keys manually by ear.  Having already made a range of tuned keys to work with, this made tuning easier and speeded up my progress in finishing the production of the two marimbas.  You can see video of me tuning a key on the video page of this website.

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The Resonator rack

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5cm diameter plumbing tube was cut at lengths that correspond to one quarter of the wavelength for each note that they would be suspended under.  The information regarding the wavelength of set frequencies is widely available on the internet and is included in my table of dimensions.  The tubes are closed rather open ended as this reduces the length the resonators need to be.  The science of this is interesting and can be accessed on web pages such as the one given in this link.

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