How to build a Marimba - (Helping Kimberly Peck)
-----Original Message----- From: Kim Peck Sent: Saturday, 20 March 2004 5:26 AM To: firstname.lastname@example.org Subject: How to build a simple marimbaDear Jim,
I am an 18 year old high school student in the United States and I have been assigned the task of building my own marimba. I have been searching and searching all over the internet for plans on how to build a simple marimba that does not require any commercially made musical instrument pieces (one of the requirements in my assignment), but there doesn't seem to be any websites that include plans or even basic guidelines. Do you know of any websites that will meet my needs, or can you provide me with some simple instructions to make a basic, compact, one-person marimba? Thank you in advance for your time and help.
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I don't really know of any sites or books that have that kind of step by step info. Most of the information you really need however is already on my website in the form of the articles on instrument building. This ranges from quite specific issues to more general ones, so you might have to sift through a bit.
What I WILL say is this. Work out what you want to achieve first - ie. just what level of professionalism you are aiming for in both looks and sound - what pitch range you want/need to cover - what size limitations you have, cost limitations etc.
1. - BARS. Start with the bars. Make your highest and lowest bars first. One they are tuned and ready to go you can graduate the length of bars in between so that that they basically form a straight line. Don't cut the planks on the diagonal though, and remember to treat the "black" notes separately to the "white" notes, otherwise your dimensions will be out when you put them together. You may decide that just tuning the fundamentals is enough - certainly its a much more fiddly process to tune the harmonics as well for the small improvement in sound it might get for you. Probably best to use a cheaper timber to start with - leave the preferred Honduras rosewood for when you have more experience and money to throw at the project. A hardish timber is best. Don't drill the string holes, or finalize the bar tuning till after you have designed the frame.
2. - SUSPENSION MECHANISM. Sometimes this can actually be the trickiest part of a marimba project. A cheap and easy method is difficult to find. Probably the best "budget" solution I have seen, is to use the little hooks or full round eyelets with self tapping timber threads that you can buy in hardware stores. With this kind of system, the best thing to stop the bars clicking against the metal, is some felt washers on the string either side of each bar. Once you've worked this system out, you can work out the dimensions needed for the frame struts that the bars will lay on.
3. - FRAME. Now you can work out the mechanics of the frame, as you have the essential measurements. There are countless possibilities depending on how many notes your instrument will have, what pitch, how portable the instrument will be etc.. Most standard instruments have two end pieces. Built into these end pieces are the holes or block of wood, or whatever will end up holding the struts supporting the bars, and the resonators. These struts may even also be the method of holding the two end pieces together, but that would mean making a permanent fixture. As most commercial instruments need to be taken apart for portability, these struts just slot in once the end pieces are held in place by a separate central cross strut with female threads at either end. A bolt passes though the end pieces and screws them to the strut. Some sort of diagonal is usually also built or screwed between the end pieces and the main horizontal strut.
4. - FINISH BARS. Once you have built the frame, (or at least enough of it) you can lay the bars in their final positions on the struts. This makes it easy to mark out the exact position of the string holes with a pencil. Once you have drilled the holes (don't forget the angle needed on the holes furthest from the middle of the instrument) you can finish tuning the bars. You wait till after the holes are drilled, because sometimes the holes will effect the tuning enough to be a pain! When carving the bars - rather than spending lots of effort with chisels or knives etc. you might consider a sanding disk on a drill. Just be careful not to let the pitch get too low. It seems you have to sand heaps to start with, but as you get closer to the desired pitch just a tiny bit can make big difference to the pitch change.
5. - RESONATORS. You can make resonators from anything that is airtight. The easier to work with and the cheaper, the better. I always use PVC pipe - the same stuff that most stormwater and sewer pipes are made of. It is readily available in a whole variety of diameters from hardware stores - or cheaper usually from plumbing suppliers. It is also easy to cut, and has a variety of end stops, elbows and other fittings available in each size. Use 1/4 wavelength resonators - ie plugged at the bottom, and open at the end under the bars. Choose diameters roughly the same as the width of each bar. The length can be worked out using v=fw where v is velocity of sound in air in m/s (check encyclopedia - I think its roughly 330m/s but I forget) - f is the frequency of the note, and w is the wavelength. There is also an amount called the "end correction" The tube needs to actually be slightly shorter than exactly 1/4w by an amount 0.61r where r is the radius of the pipe. This means the length you want is (v/f)/4-0.61r. Even so its best to be sure not to cut to exactly this first time, because you can't shave a bit more back on once you've cut it. You will Have a bit of free play in the sliding of the end caps and any bends you use, so be a bit generous in your initial measurement, then cut shorter by a bit, but not by more than the free play you have with the cap etc. Put the pipe under the actual bar an strike the bar whilst sliding to see what works best. If its best as short as you can slide it, then you can always shave off a bit more and repeat. Once you've found the best position, mark out the position of the cap and/or joins on the pipe, and glue them with PVC glue. It bonds pretty fast, so get it right to the perfect position straight away. Once you have all your resonators together, you can join them all up, and support them in the frame using some 1-3 mm aluminium strip. Use airtight rivets to join the strip to the pipe.
Hope this is helpful - don't hesitate to ask if you have specific questions.
answers by Jim MCCarthy - 01/04/2004
For more help on instrument building you can email Jim.