I am a mallet percussionist who loves the marimba. About four years ago I had a problem. Though I loved percussion, I had no way of practicing at home. There were cheap options. I could have bought a bell kit. But I hate the sounds they make. I wanted a very large five octave marimba but didn't have the money to simply purchase one (7000+ dollars). So I decided against all common sense I would build one.
The goal: build a five octave marimba, without spending a fortune. Use whatever supplies are available to keep the cost low. (The keys are made from an oak tree which was struck by lightning several years ago!)
I hope this instructable will inspire others but I want to give a word of warning. This is an extremely ambitious project and will likely takes a year or two for the average individual (like me) to complete.
Some notes about the included audio recording:
The marimba was playing using the same mallet across the entire five octave range. for this reason, the mallet I chose was a little too hard for the lowest note, and a little too soft for the highest note.
Step 1: Materials
For now let me just state the basic components of a marimba and the materials you will need.
The Bars - this is where everything begins. The bars can be made from nearly any material, but to qualify as a marimba it must be wood. Feel free to experiment with different types of wood before construction. But it is important for the wood to be completely dried out (not green at all). My oak material came from a tree which was struck by lightning.
The Frame - for me, this was the next step after building the bars. The frame can be made from anything. This includes wood or even steel. Use whatever you are comfortable with.
The Resonators - Nothing difficult here. Though anodized aluminum is very pretty PVC pipe works just as well.
Those are the basic parts of a marimba but you will also need some specialty equipment.
Musical Tuner - How much you invest in a tuner will be reflected in your marimba. If you just want something to practice with (like me) then a 30 dollar tuner will do just fine. Otherwise, if you want to tune overtones, use a strobe tuner (300+ dollars).
Belt Sander - You will be using this a lot so get something comfortable.
Drill - You will need to drill holes through the width of the bars for the marimba string. I suggest a drill press but a hand drill will work just fine.
Table Saw - for making all those cuts.
Band Saw - not essential but recommended if you will be cutting bass notes.
Miter Saw - really handy with the frame and resonators
Step 2: Cutting the Bars
By the way, a higher pitch marimba will require much less sanding and can be finished relatively quickly.
Once you have your goal and dimensions in mind, use a table saw cut the wood. try to keep the grain running the length of the bar and avoid big knots in the center of the bar. If it looks nice it will likely sound nice. At this stage you're only aiming for a brick like shape. Don't worry if it is a little rough.
Don't worry about tuning the bars yet. That comes next.
Step 3: Tuning the Bars
Once you are ready use a belt sander to begin removing mass in small increments. Feel free to smooth out the surfaces and add any artistic effects you may desire. Periodically, check your progress with the chromatic tuner. You can do this by holding the bar approximately at one of the nodes and striking the center. As you remove mass, the bar's frequency will decrease. If you are tuning a bass note I suggest you cut a chunk out of the bottom first. This should be done with a band saw and will make sanding a lot faster.
It is important not to sand too much too fast. If you do, the bar will heat up. The change in temperature will affect the tone produced. So when tuning the notes try to keep the temperature consistently around room temperature.
If you make a mistake and sand too much (making the note flat) don't worry it can be fixed. I found the simplest way was to trim the ends of the bar, making the length shorter. 1/8 of an inch goes a long way.
As previously discussed keep in mind temperature will have a great impact on each bars frequency. Just try to keep an "optimum operating temperature" in mind. Mine sounds great at 80 degrees Fahrenheit. But it is twenty cents sharp at 50 degrees.
Step 4: Tuning the Overtones
OK... To tune the overtones you will need one of two things,
A. Strobe Tuner
B. Audio Spectrum Analyzer
I suggest the Strobe Tuner especially if you are a musician. Personally I consider Peterson Strobe Tuners to be the best and they also make a Strobe Tuner app for the Iphone/Itouch. I only included the Spectrum Analyzer to give you an alternative.
Yes you can tune the fundamental frequencies and the overtones of all bars just by shaping the undercut of the bar.
Before we get into how to shape the curve, let's review the proper ratios between the overtones. For Marimba and Vibraphone builders it is 1:4:9.88. For Xylophone builders it is 1:3:6.
Now, to tune the overtones you should follow the template in the pictures below.
To tune the Fundamental frequency (1), sand in the center.
To tune the second overtone (4), sand just outside the center
To tune the third (9.88), sand close to the ends of the arc.
Now here is where it gets tricky...Changing one overtone, will change the frequencies of the other two!
For this reason, you have to first get the ratios between frequencies correct, and then sand evenly across the curve until you arrive at the fundamental (hopefully with the ratios intact.)
If you mess up and tune something too low, you cannot (to my knowledge) fix the problem without reducing the length of the bar.
Additionally, you will notice the overtones become increasingly more difficult to tune as you begin to work with higher and higher notes. This is because the sample size/duration/sustain of the higher notes become shorter and shorter. This also makes the overtones more difficult to hear. So do you want to tune the overtones of the upper register? I don't know. You'll just have to play it by ear. (I'm sorry... couldn't resist a bad pun)
I highly recommend you read this research article:
Nonuniform Beams with Harmonically Related Overtones for use in Percussion Instruments
by Felipe Orduna-Bustamante
published in the Journal of the Acoustical Society of America
Step 5: Building the Frame
This is a time to get creative. There are only a few rules to a marimba frame so as long as you abide by those rules; you don't need to worry about how the frame might affect the quality of sound produced by the instrument. And those rules are...
1. The bars must be supported by "marimba string".
2. The string must be supported by braces in between the marimba keys. (Next step.)
3. The frame will also hold your resonators. (if you choose to build them).
Bear those three rules and facts of a marimba frame in mind as you craft it and you should be fine. I suggest you lay out your tuned keys on a large flat surface to get the dimensions for your frame.
You should also consider how high you want the playing surface to be off the ground.
Note in the pictures the frame follows the path of the bars and the string that will later run through the instrument.
Step 6: Adding String Supports
I suggest aluminum rods. Use a band saw to cut the rods to an appropriate length. They should be long enough to accommodate your thickest bar. You will need to split one end of each support to so the string can lay in it. I suggest mounting each rod in a vice grip and using a hack saw to split the aluminum. Then use a screw driver and a good old fashioned hammer to open up the supports into a nice "Y" shape.
If you are recycling some old aluminum like I did, you may need to put a coat of paint on them so they all look uniform.
Finally to mount the supports into the frame you will need to drill holes into the frame at the appropriate intervals for the supports. Your drill bit should be a little small than your supports. Once done, return to the screwdriver and hammer to coerce the supports into their new home.
Notice in second picture below you can see a nylon string running though the braces. This should give you an idea of how it all fits.
Step 7: Stringing the Bars
These holes should be drilled through the nodes of each bar. (Again, you can find the nodes by figuring out where the bar vibrates least when you strike it in the center.) Also, you should drill the holes on each bar an equal distance from the playing surface. If you don't you won't get a level surface.
Once you're done, that's it! Play a tune! Be happy with yourself! But it you want to go the extra mile, carry forth to the next step.
Step 8: Resonators
The material for the resonators can be almost anything. Just look for something that will hold water without leaking. That is essentially what you're doing. For me, PVC pipe works great. You will need the tubing and plastic test caps.
Now for some physics! Don't worry this is really simple.
L = 340/ (4f)
Length (in meters) is equal to the speed of sound divided by the quantity of four times the frequency of the note.
Frequency is measured in Hertz. You should use your mad Google-ing skills and look up the frequencies of your notes if you don't already know them.
I suggest you cut your resonators a little longer than you need. Trim off a little at a time, and hold it under the correct bar as you play it. When it sounds good and full, you're done with that resonator. Relax. This doesn't take that long and you won't make an extremely costly mistake.
Exactly how you mount your resonators under your bars us up to you. You just need to get them there. Don't be afraid to drill screws into your resonators to hold them (if you choose to do things that way). The resonators will still resonate. If you are making resonators for bass notes, you can curve and bend your resonators to fit under the instrument. Of course the beauty of PVC is you can buy PVC joints that are already bent.
Step 9: You're finally done!!!
So go get started and play something "epic" to celebrate your success.
Ah but wait! Perhaps you have no mallets to work with. If this is the case continue forth!
Step 10: Malllet Wrapping Parts and Materials
The stick should be made of wood. The material for the core is up to you.
3/8 inch dowel rod (3/8 is just my personal preference. Use whatever is most comfortable.)
Round Core (In the pictures following, I use a "bouncy ball" I bought in the Grocery Store for 25 cents.)
Needle (a relatively big one)
Some notes on the Core
You have a lot of options here. The material for the core will have the largest impact on the tone produced. A hard core like a wooden crafts ball will work well for the upper ranges of a marimba, but will sound horrible on the lower ranges. For a relatively soft core, I've found "bouncy balls" or rubber balls are the best bet.
Step 11: Assembling the Stick and Core
Once you have a hole, use some wood glue or epoxy to connect the core to the stick.
Step 12: Cut the Stick and Sand the Edges
Nothing wrong with that. It is just my personal preference to do it this way.
Otherwise I'm never really sure long to cut the stick to make it even with the other mallets.
Once the mallet is cut to length, take it to a sander and remove those uncomfortable 90 degree angles.
Step 13: Wrapping the Mallet
Start by tying a knot just below the core. Then, begin wrapping over the top, and then under.
Over, Under, Over, Under....
Be sure to count the number of wraps around the mallet. If you want a set of mallets to sound the same, the number of wraps must be equal. Each time the yarn crosses the top of the mallet, that's one wrap. If you're still confused about this, watch the YouTube video.
The mallets I'm wrapping here will have 100 wraps each.
Step 14: Crowning and Finishing the Mallet
Tie the free end of the yarn to your needle.
Now to crown the top and bottom of the mallet. I prefer starting with the top.
You need to push the needle in (at an angle) at the top of the mallet, and pull it out.
Do this over and over, going in a circle around the mallet head. This process makes sure your hard work won't come unraveled soon.
Once you finish with the top, the same needs to be done at the bottom.
After you're finished, I suggest crowning once more at the top, but this time you will tie a knot there. (As in the pictures.) Don't worry too much about the knot. I've wrapped several sets of mallets and only once have I had this knot come undone.
Step 15: Some Examples
And if you are curious about the white/black mallets, I used yarn which transitions between the two colors. In other words, those white/black mallets are wrapped with one continuous stand, not two.