Building a Simple Marimba - (Discussions with Pat)
-----Original Message----- From: Pat Rix Sent: Friday, 29 August 2003 6:15 PM To: firstname.lastname@example.org Subject: help!Dear Jim
I am an Adelaide based writer/composer working on a community music-theatre work to commemorate the Jubilee 150th of Melrose, the first and oldest town in the Flinders Ranges. The show is on the October long weekend and one of our farmers wants to make a simple marimba.
I’m wondering if you have a straightforward set of instructions you could pass on.
Years ago I made a simple version up in a Queensland rain forest but I can’t for the life of me remember the measurements.
Since our farmer has the wood, a circular saw and lathe he is keen to get cracking this week, or should I say yesterday.
We’d all appreciate some help as the township is very small and doesn’t have a library.
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I don't think such thing as a "straightforward set of instructions" exists. [UPDATE - they do now - get them here!] Your measurements will depend a bit on what timber you are using for the bars. Its not really fixed though, as you can get the same note from different size bars depending on the amount of carving done to tune them. For the sort of instrument I suspect you are after you won't have to worry too much about tuning all the overtones - just the fundamental, so it is really just a matter of finding or cutting a bit of wood to the size you want the bar to be. Then you find the nodal points (points of no vibration) where you drill a hole for the string to go through that suspends the bar. Some simple instruments just have a hole drilled through the face of the bar for a wood screw to go through a s a bar-suspension mechanism. You can find the nodes by just hitting the bar in the middle while holding it at a single point, and see where you get the best vibration - it will be roughly 1/4 the bar length from each end. If you want to be really precise, you can lay the bar flat on an old blanket or something and sprinkle it with some fine sawdust or similar. After hitting the bar to get it vibrating a number of times - the sawdust will tend to gather along the nodal line. Once you have the nodal points, drill the holes, suspend it, and start carving. Carve wood from the middle area of the bar till the note produced lowers to the one you are after, I would strongly recommend just using PVC pipe for the resonators. Choose a diameter pipe roughly the same as the bar width and cut it to length - 1/4 of the wavelength of the note the bar makes. Use v=fw where v is velocity of sound in air - f is frequency of note and w is wavelength. This length of pipe will be a bit longer than what you need, but is the best place to start. Get a push on cap for the pipe. Put it under the bar and hit the bar, and listen for the resonance in the pipe. You will have some room to work with as the cap can slide up or down a bit to adjust the length. Chop the pipe down bit by bit with a hacksaw till you are able to get a good resonance - mark the cap position with a texta, then glue it on to line up with the mark.
Unfortunately I don't really have the time at the moment to really get involved in this sort of project, but if you have specific questions, please feel free to ask - there should be a bit of information accumulated in the articles on the website as well.
My best advice is to try to get hold of a bloke called Jon Madin. He specializes in this sort of instrument, and project. I don't have any contact info sorry, but he is known a bit round the traps. He helped out with some projects for the Bundaleer event at Jamestown, so there might be some people there who can lead you in the right direction.
answers by Jim MCCarthy - 09/09/2003
For more help on instrument building you can email Jim.