Build machines that make music—including some that play themselves!

When you start to invent your own instruments from everyday objects, your brain begins to pay extra attention to ordinary sounds. If you’ve ever heard the boing of a door stopper spring when you hit it with your shoe, the scritch scritch of an old pair of scissors, or the knock knock knock of a window shade in the breeze and thought “That sounds like the beginning of a song!” then you’ll enjoy the projects in this chapter.

Some of the musical machines you’ll learn about in this chapter are based on popular contraptions from the past. Others are inspired by artists of today who have come up with unique ways to turn accidental sounds into music. You’ll need to use concepts like standing waves and nodes that you encountered in earlier chapters and combine them with elements of simple levers, springs, and more to make your musical machines move and play. You’ll also get to think about what new sounds you can create and unusual ways to make them happen.

Shake Things Up with Resonance and Timbre

As you know, instruments create music by vibrating, which causes the air around them to vibrate. To make a soft instrument sound louder, it helps to add a resonator. A resonator vibrates at the same frequency as the note you are playing, which adds energy to the sound wave and raises the volume. If an instrument doesn’t have a resonator built in, you can use another object as a resonator to help increase the sound.

You can use this trick with several of the projects in this chapter. For example, the thumb piano is a quiet instrument that you hold in your hand and pluck. Place it on a box, inside a bowl, or even on a table, however, and suddenly the sound explodes. In Africa, where the thumb piano got its start, players use hollow gourds to amplify the sound. If the inventions you create are hard to hear, try setting them on top of an empty box or leaning them against a piece of furniture and see if the sound improves.

Something else you will discover as you look for objects to add to your inventions in this chapter is how different materials can affect the tone. The timbre of an instrument is the type of sound it makes. As you experiment with various items, pay attention to the way metal, wood, glass, and other materials make your instrument sound—even when the notes are the same. You may even want to make several versions and compare them to see how they give your instrument its own personality.

Project:
Thumb Piano

The thumb piano is a traditional instrument from Africa, where it is known by several names, including kalimba and mbira. It is a type of lamellophone, an instrument with strips or rods that you pluck. The thumb piano consists of a small body with a row of tines on the front of the instrument that are attached near the top. These are similar to the keys on a regular piano—each one plays a different note. To play the thumb piano, you hold it in both hands in front of you, like the way you hold your cell phone when you are texting, and press down on the tines with your thumbs. As the tines spring back up, they vibrate from the point where they are attached (or the bridge, if there is one) down to the end. The pitch depends on the length of this vibrating segment. Unlike most instruments, the notes on a thumb piano do not usually go from lowest to highest. Instead, they are arranged in a V shape or spread out like a folded paper fan. The longest tines that play the lowest notes are in the middle, and the shorter tines that play higher notes are on the sides.

The following directions show you how to make a thumb piano that doesn’t require special tools and a kind of bridge that lets you use a variety of common materials for the tines.

1. First, choose a body. It should be small enough to hold in your hands easily, about the size of a cell phone (but thicker). When deciding on the width, also think about how many tines (which you will choose in the next step) you can fit in a row across the body.
2. The tines you choose for your thumb piano should be narrow enough to allow you to fit five or more across the width of the body. They can be longer than the body if you don’t mind having the excess hang off the top. If you want to cut them shorter, wire cutters work well for most kinds of materials. (See the earlier Safety Warning.)

   

3. Choose rods that will hold your tines down securely, such as pencil stubs or chopstick pieces. The secret to making your thumb piano sound good is to attach the tines as tightly as possible! The rods should be a little longer than the body is wide. For the bobby pin method, you need two. For other materials, you need four.

   

4. Time to attach the tines! If you are using whole bobby pins, the method is simple: place the bobby pins in a row near the top of the body with the flat side down. Arrange the pins so their ends make a V shape. Insert one rod inside the pins so it lies across the entire row. (Important:Do not try to bend the pins open—let the rod push them open.) Place the other rod underneath the body so its ends line up with the top rod. Wrap a rubber band around one end of the top and bottom rods. It should be just tight enough to hold the rods in place. Repeat with the other end. At this point you can try plucking the tines to get an idea of what pitch they play. You can adjust them now, but you will tune them exactly later. To finish, take another rubber band and wrap it around the end of the rods on each side, right over the first rubber band. This time make it as tight as possible. The two ends should be equally tight.
5. The method for other kinds of tines is a little different. Start by connecting the rods above and below the body with the first set of rubber bands. Then slide the tines under the top rod. Next, take two more rods and slide them under the tines. They should go on either side of the rods with the rubber bands. The rods act like the bridge on a guitar to hold the tines away from the body. Finish by tightening up the top and bottom rods that are holding the tines in place with the second set of rubber bands.

   

   

6. Now you can tune your thumb piano. Lean the instrument against a table, or set it on top of a hollow box or other resonator (see suggestions in the Materials list). Hold it in both hands and use your thumbs to pluck each tine by pressing it down briefly. Adjust the tuning of each tine until you are happy with all the notes. To raise the pitch on a tine, push it toward the top of the thumb piano. This shortens the part of the tine that is vibrating. To lower the tone, push the tine toward the bottom of the thumb piano to make the vibrating section longer.

Troubleshooting tips:

• The tighter the tines are held down, the clearer the vibrations. If none of the tines sound good, try squeezing the top and bottom rods closer together. If you used rubber bands, loop them around one more time. Or use a zip tie to pull them tighter.
• If just one or two tines are loose, look for replacement tines that are a little thicker.
• If a tine on the bobby pin version is buzzing, check to see if the upper end of the bobby pin (where it bends) is raised off the body. You can fasten it down so it is held tight against the body by looping a separate rubber band through the bobby pin and around the board. Or run a craft stick or coffee stirrer through all the bobby pins near the bends. Attach it to another stick under the body, as you did with the rods.
• If you can’t get one particular note to sound good no matter what you do, it may be causing sympathetic vibrations in another part of the instrument that muddy the sound. Try skipping that note altogether and make that tine higher or lower in pitch. Shift it around until you find a position that sounds better.

Project:
Musical Marble Run

Marble runs are fun to watch—and when you add your own bells and shakers, they’re also fun to listen to! This bare-bones marble run may seem simple, but it’s got what robotics scientists call a “programmable body.” That means you control the sounds it plays by how you place the ramps and noisemakers. Use the power of gravity and the concepts you learned about how instruments such as idiophones work to make it play faster or slower, softer or louder, and higher and lower. That’s how you turn a basic toy into a real Musical Invention!

1. The bamboo skewers you are using for your building material have sharp points. Use the wire cutters to snip the points off. Wear eye protection and point the skewer point away from yourself and other people before you snip.

   

2. Also cut several skewers into pieces 1½ inches (4 cm) long. Set these aside where you can grab them as you need them.

   

3. The marble run consists of two towers that hold up rows of slanted tracks. The tracks have a narrow end and a wide end. At the narrow end, the two tracks are just far enough apart to allow the marble to roll along them. At the wide end, the marble is able to slip through to the next level down. To help you figure out the measurements of your system, create a sample set of tracks. Take two skewers. Lay a marble on the work surface. Line up the skewers on either side of the marble. This is the widest point between the tracks. You should be able to lift the skewers up easily, without rubbing the marble. Take one of the short pieces of skewer you cut and glue it across the two tracks to hold them in place, about ¼ inch (6 mm) from the ends of the tracks. The other end of the skewers should be almost touching. You can use the thin edge of a tongue depressor as a spacer while you glue another short piece across the other end.

   

4. To make the tower supports, take a skewer and poke the pointed end into a small bead (preferably a bead with a flat bottom). Secure it with a little hot glue. (Use a piece of scrap wood to wipe off any excess glue that leaks out.) Let it cool. Repeat with three more skewers, for a total of four.

   

   

5. Now it’s time to assemble the side towers. They are made up of two of the sticks with the beads, with a tongue depressor as a base. To figure out the proper width of the tower, take two of the tower skewers with the beads on the end and lay them down side by side. Fit the wide end of your sample track around them. Spread the tower skewers apart until they touch the inside of the track skewers. Glue a crossbar (short piece of skewer) across the two tower skewers to hold them in place, right above the beads. Check to see that the narrow end of the sample track fits inside the tower. If it does, then glue the bottoms of the beads onto a tongue depressor. If not, adjust everything by carefully peeling apart the glued sticks and regluing them in the proper positions. Repeat with the other tower—but the crossbar for the second tower should be about 1 inch (2.5 cm) higher than on the first tower. Measure the position of the higher end of the track and mark it on the tower in pencil before gluing.

   

   

6. To make the bottom set of tracks that will help support the frame, set two skewers inside the tower sticks, resting on the crossbars. Leave about ½ inch (12 mm) of the skewers hanging off either end. Attach the skewers to the crossbars with hot glue. Before going on, roll a marble down the tracks to make sure they’re tilted enough—if not, carefully remove the higher crossbar, raise or lower that end of the tracks, then reglue. Next, glue crossbars onto the tops of the tower sticks, making sure that the width of the towers stays the same at the top and the bottom. Connect the tops of the towers by gluing two skewers on the outside of the towers, just below the top crossbars. Test again to make sure a marble can fit between the skewers at the top of the frame.
7. Now you can add tracks inside the frame to make the different levels. You can control the speed of the marbles by altering the slope of the tracks. The steeper the angle of the tracks, the faster the marbles will roll. The slant will also determine how many sets of tracks you can fit into the framework of the marble run. The sample system in the photos has six sets of tracks. Here are some tips to keep in mind:
   • Like the sample track that you made, every set of tracks has a narrower end, where the skewers are glued to the inside of the towers, and a wider end where the tracks are glued to the outside of the towers.

     

   • The narrower end of the tracks is always higher than the wider end.
   • The tracks will zigzag—on one level the tracks tilt down to the left, the next set tilts down to the right.
   • The wide ends and the narrow ends of the tracks alternate—the wide end of one level sits above the narrow end of the level below it. The marble will drop from the wide end of one level to the narrow end of the level below it.
   • Use your sample set of tracks to figure out where the high and low ends of your track will be connected to the towers. You can vary the slope of each level, or just make them all the same. If you want your marble to bang into or bounce over noisemakers, tilt the track so it is a little steeper. That will give your marble more speed and keep it from getting stuck.
   • You can also add speed by increasing the distance the marble has to drop between one level and the next. The drop should be at least ½ inch (12 mm), but you can make it as much as 2 inches (5 cm).
   • Be sure to leave enough room between levels so you can hang noisemakers like keys and washers.

   

8. You already have the bottommost tracks in place. To build the next level up, take your sample set of tracks and insert it between the towers. Follow the guidelines in Step 7 to position it correctly, then mark the position of the ends on each tower. Remove the sample and glue crossbars onto the towers at the marks. When they are dry, rest two skewers on the crossbars. At the lower crossbar, glue the skewers to the outside of the tower. At the higher crossbar, glue the skewers on the inside of the tower.

   

9. Test the new level with a marble. Then continue adding on levels the same way until you reach the top of the frame.
10. To keep the marbles from falling off the sides of the tracks, make “guard railings” by gluing skewers on the outside of the towers, a little above each track. (They should be about half as high above the tracks as the marbles are tall.)

    

11. Once your marble run is operating smoothly, you can start to add noisemakers. These can be attached to crossbars glued to the underside of the tracks where needed. Be sure to test them before you attach them permanently to make sure they don’t slow or stop the marble along the track. Here are some ideas:

    

    • Hang a bell over the track. If needed, make the clapper longer so the marble hits it as it rolls underneath.
    • Hang keys, metal washers, or recycled mini wind chimes from above.
    • Make a clackity “raft” with mini craft sticks. Line up the sticks, attach two sticks across the raft on both sides, above and below, and tie these sticks together with string. Hold the whole raft in place by tying another craft stick to a crossbar loosely fastened across the tracks.

      

      

    • Attach a string of beads between the tracks just high enough for the marble to bump along as it rolls downhill.
    • Save large bumpy noisemakers—such as large wooden beads or metal bottle caps—for the spot right below the drop from one level to another. That will give marbles enough extra momentum to get over the rough spots.

      

    • Use a small spoon to make a seesaw on a crossbar below the track that lowers the marble to the next level. Hold a loop of stretchy string or a rubber band under the crossbar and hook it over the ends from underneath. Then take the handle of the spoon and thread it between the stretchy string and the crossbar, with the string on top. Balance the spoon so that a marble can roll over the handle and drop into the bowl of the spoon, where the weight will tip it downward until the marble rolls out onto the next level. The elastic makes the spoon return to its starting position, ready for the next marble.
    • Be sure to end the marble run with some kind of noisemaker, such as a wind chime laid crossways across the railings.

Music Box Engineering

Music boxes are known for their tinkly sound. But wind-up music boxes are also finely tuned machines. Turn the key to tighten a spring, open the lid to release the catch that lets the spring unwind, and gears and flywheels start to move the mechanism at just the right speed. The music is produced by a rotating cylinder studded with tiny pins. As the cylinder (known as the drum) slowly spins, the pins pluck the teeth of a metal comb. The teeth on each comb are different lengths and thicknesses, depending on the notes needed for the melody each box plays. Every part of a music box takes artistry and expertise to create.

Music boxes also have inspired musical inventors to get creative. Like thumb pianos, the teeth can be made out of any material that makes an interesting sound when it is plucked or tapped. Our version uses assorted wire springs, but you can try other kinds of noisemakers as well.

Project:
Experimental Music Box

1. The “comb” of the Experimental Music Box follows the same basic design as the Thumb Piano earlier in the chapter. You will attach coffee stirrers to a wooden board using rods and rubber bands. However, in this case, the coffee stirrers are simply used as anchors for the springs. The board then fits into the box (which also holds the drum you turn to pluck the springs). The first step is to figure out where to place the springs. To get started, take the board and stand it on end inside the box. Then lay a pencil (or other rod) so it rests on the sides of the box next to the board. Draw a line above the pencil across the front of the board.

   

2. Take the board out of the box, still standing on end. Take a coffee stirrer and stand it up against the front of the board. Mark the height of the line on the coffee stirrer. Now attach a spring to the coffee stirrer, just above the line. To do this, squeeze the stick between the coils of the spring as close to the bottom as possible. Turn the spring (like unscrewing a bolt) until just the bottom tip of the wire is below the stick. Take the pliers and pull the tip until it wraps around the far edge of the stick. This will hold it in place. Repeat with the other springs.

   

   

   

   

   

3. Lay the board down and line up the coffee stirrer sticks with the springs attached so the springs are sticking up. They should be evenly spaced. Leave room on either end. If any of the springs are angled toward the spring next to them, adjust the spacing as needed. Place a pencil or other rod on top of the sticks, next to the springs. Place another pencil on the back side of the board, and attach them with rubber bands, just like you did with the Thumb Piano. Do the same with the other pair of pencils on the other side of the springs. When you’re done, trying plucking or scraping the springs to see if they are tight enough to make a good tone. If the pencils curve a bit in the middle and make the middle stick loose, wedge a shim (such as a piece of paper or a second coffee stirrer) behind it. If you want to secure the ends of the sticks, press them down with a tongue depressor held in place with pushpins.

   

   

4. Put the board back into the box. Push it all the way back against the side of the box so the springs stick out toward the middle. Take two of the clothespins and clip them over the sides of the box to hold the board in place. To make a tracing of the springs to help with positioning the pins on the rotating drum, hold a piece of paper flat under the springs and trace around them.
5. Now it’s time to make the drum. You will use screws as pins to pluck, scrape, or tap the springs to get them to make a sound. To begin, take your wooden rod or rolling pin and lay it across the top of the box, leaving a little space between the rod and the longest spring. Use more clothespins as guides to hold the rod in place. Make sure at least one end of the drum is sticking out far enough past the clothespins for you to hold onto it in order to rotate the drum. Wrap some tape around the rod.
6. To keep the rod from sliding side to side, wrap rubber bands around the ends of the rod just outside the clothespins to make a little ridge as guides. Wrap some tape around the rod to keep it from rubbing against the clothespins or the side of the box. (See Figure 3-50, later in this activity.) To prevent the rod from rubbing against the box, loop loose rubber bands around each pair of clothespins to hold them together. Slide the rubber bands down until they are just above the side of the box. Let the rod hang in them like slings. You can also stick a strip of peel-and-stick foam tape along the inside of the clothespins, in a “U” shape.

   

   

7. Now it’s time to attach the pins. For the first pin, find a screw that is a little bit longer than the distance between the rod and the first spring. Important: The head of the screw should be wider than the spring. Make a mark where the screw should go—hold a stick straight across from the spring to the rod to help you line them up. Take the drum out and use a pushpin to make a starter hole at that spot. Then take the screw and a screwdriver and carefully turn the screw a few times into the wooden rod. Test the screw by replacing the drum and turning it. The screw should touch the spring to make a sound, but not get caught in the coils. If you need to adjust the distance, use the screwdriver to turn the screw further into or out of the drum.

   

   

   

8. Mark the spots for the remaining pins. If you want to play two or more notes at the same time, line up the pins for those springs in a row straight across the drum. If you want to play the notes separately, place them at different spots around the rod. Insert the screws as you did in Step 7, testing after you add each one before you go on to the next screw.

Project:
Origami Paper Popper

Anything that can create pressure waves in the air can produce a sound. And anything that produces a sound can be used to make music—even sheets of paper. An Origami Paper Popper makes an explosive crack! when you flick it. It is a type of free aerophone, like the bullroarer you swing around your head from Chapter 1, which makes the air around it vibrate directly. Although typically used for impressing friends on the school playground, you can also use your Origami Paper Popper as a percussion instrument in your Musical Inventions band.

1. Lay the sheet of paper in front of you horizontally, so it is longer from side to side. Take the top edge and fold it down so it meets the bottom edge. Press the crease flat, so it is nice and sharp and divides the paper evenly in half. Then open the paper again.

   

2. Take the top edge and neatly fold it down to the crease you just made across the middle of the paper. Make these folds as precise as you can so the folds are as thin and as exact as possible. Sharpen that crease and repeat—that is, fold the new top edge down to the middle crease.

   

   

3. The top half of the paper is now folded up several times. Take the folded top edge one more, and fold it down along the original middle crease. Then fold the folded top edge one last time. You now have a big fat folded strip across the top of the remaining paper.

   

4. Flip the paper over so the folded-over flap is against the table. Take the right edge and fold it over so it meets the left edge. Make the crease as smooth and sharp as possible.

   

   

   

   

5. Finally, “load” the popper so it is ready to go. To do so, turn the paper so the flap is on the left. (Note: If you are left-handed, reverse the left and right directions in this step.) Hold the paper by the top corners. Carefully pull the upper right-hand corner out and down, so that the crease opens up into an upside-down V. The sides of the V should be fat and rounded. Stop when just the tip of the right-hand corner is still visible. Move your right hand to hold onto the bottom corners of the V. You should now be holding the popper like a backward paper airplane, with the bigger end of the open rounded “tunnels” facing forward, and the point facing the back.
6. Quickly flick the popper downward. The rounded parts should pop open with a loud snap! If it doesn’t work the first time, try opening the tunnels up a little with your fingers to give them a head start.
7. To reload the popper for another pop, push the now-opened flap back into the position it was in at the start of Step 6. Your Origami Paper Popper should be good for several snaps!

Project:
Flapping Paper Strips

Paper isn’t just for popping. You can use paper to create quieter, more subtle sounds by crinkling it or letting it flap in the breeze.

1. Cut one or two thin strips of paper. Tape the paper to the front of the fan.
2. Turn on the fan to see if the paper flaps and makes interesting sounds. Try different widths and lengths, or try making cuts in the end of the paper to create a fringe.

Extension:

• If you have a drum or tambourine, tape a strip of paper to the drumhead and aim the fan at it. See if it will create a varying beat as it flaps against the drum.