Recording and listening devices let you enjoy music from afar and share it with others.

Until the late nineteenth century, pretty much the only way to hear a musical performance was to be there, live, in person. Two inventions—the phonograph and the radio—changed all that forever.

Earlier instruments let you listen to “prerecorded” performances by playing music automatically. They included wind-up music boxes (the inspiration for the project in Chapter 3) and player pianos (which used paper rolls with holes punched in them to trigger piano keys). Those kinds of machines could be programmed like primitive computers to play the same song over and over. But the phonograph and the radio made it possible to hear real musicians as they were playing. The phonograph captured a musical performance (or any other kind of sound) on a recording that you could play back later. Anyone with a record player could listen to that recording. The radio sent live performances or recorded music (as well as news, sports, comedies, and dramas) out “over the airwaves.” Anyone with a receiver could tune in and hear the broadcast, anywhere within reach of the radio station’s signal.

After the arrival of the phonograph and radio, instead of going out to hear a concert, you could enjoy a performance at home. Instead of having to learn to play an instrument, you could turn on a machine and create music instantly. The tradition of family sing-alongs faded. At the same time, lots of future musicians got their start by sitting alone with a record and copying their favorite performers. However, recorded music had its downside too. Listening to a song being played the exact same way, over and over, made it harder for some people to enjoy live performances, with their variations and mistakes.

The phonograph and the radio even changed the way music was made. Songs became shorter, and serious works were broken down into several parts, so they could fit on a record that was only three minutes long. Record companies and radio stations began to divide music into categories to make it easier to sell. If you were a fan of jazz or country or rock and roll, you would look for a record label or a station that featured your favorite style.

Today almost all music is stored as digital files, the same way computers store other kinds of data. Instead of collecting records, tapes, or discs, more and more people are downloading digital albums to their audio devices or listening to online subscription services. Even traditional radio broadcasts are slowly disappearing as satellites make it easier to pick up stations from around the globe. The projects in this chapter are all based on older technology that will take you back to the beginnings of music recording. You can re-create these early means of sharing music—and learn a lot about history and science in the process.

What Makes Phonographs Go Round

Although modern record players are powered by electricity, the process of creating sound from a record is purely mechanical. In fact, the first phonographs were simple devices that you turned by hand, and they let you make records as well as play them.

A phonograph recording is basically a round object that spins around, with a long groove cut into it. As you cranked the machine, the cylinder would roll around like a rolling pin. The groove started at one end and wrapped around the tube in a spiral until it reached the other end. A modern record is shaped like a flat disc and has grooves on both sides. The grooves on a disc start around the edge and spiral around toward a hole in the center. The hole fits onto a little knob on the record player called a spindle, which holds the record in place on a spinning turntable.

It’s the grooves in the records—or rather, tiny bumps in those grooves—that produce the sound. To make a record the old-fashioned way, you start with a blank disk or cylinder with a smooth surface. The phonograph has a needle, also known as a stylus, that cuts into the record and creates the grooves. A thin membrane called a diaphragm connects to the needle. Sound waves directed toward the diaphragm make it vibrate. The vibrations of the diaphragm make the needle shake. And as the record spins, the movement of the needle cuts a bumpy groove in the record.

Here’s the amazing part: to play the record back, all you need to do is run the same process in reverse! First, you place the needle back at the beginning of the groove and start the record spinning. As the record turns, the needle rides along in the groove, and the bumps in the groove make the needle bounce along, ever so slightly. The shaking of the needle is passed along to the diaphragm and causes it to vibrate. And the diaphragm’s vibrations spread to the air in the form of sound waves—which are exact copies of the original sounds that made the bumps in the first place!

Project:
Manila Record Player

A no-frills, nonelectric record player is easy to design. All you need is a turntable and spindle to hold the record so it can revolve smoothly, a tone arm and needle to ride over the bumps in the record’s grooves, and a diaphragm to pick up the needle’s vibrations and pass them along through the air in the form of sound waves. Early hand-cranked phonographs also featured a horn to direct the sound waves toward listeners.

This one-piece record player made out of a manila folder was inspired by a paper version from Instructables.com user Plugable. It’s fairly loud, even without a horn to amplify it. Once you’ve got it working, you can invent some improvements of your own!

1. To make your record player, start with the manila folder. One half will serve as the base of the record player, where the spindle is attached. The other half will serve as a combination tone arm and diaphragm. This half holds the needle and transfers its vibrations into sound waves in the air. If one side of the folder has ridges, use the smoother side as the turntable.

   

2. First, mark the spot for the spindle. Open the folder and place the LP so its edge almost touches the spine of the folder (where the folder folds). Take the pencil and trace inside the hole at the center of the record. Remove the record.

   

   

3. Take the point of the pencil and poke a hole inside the circle you just drew. Push the pencil in until the hole is as big as the circle. Flip the folder over. Cut or tear away any shreds of paper from the folder around the edge of the hole. Take the rivets and find the longer, narrower half. Press it into the hole. Make sure it sticks up above the inside of the folder. This is your turntable and spindle.
4. If the front half of the folder has a tab, trim it off so the edge is straight. Then take the front and fold it in half so the edge meets the inside of the spine. Make the crease where you fold it very sharp. Draw a line to show where to make a second crease between the original crease and the edge of the folder. The two creases will bend in the same direction, about ¼ inch (1.25 cm) apart. Score the line by running something hard but not sharp along it, such as a screwdriver. Then fold along the line.

   

   

   

   

   

   

5. Take the needle and attach it to the center of the front half of the folder, on the outside, by pushing it in through the cardstock and out again. The point should be hanging off the edge slightly and should be tilted toward the right. Open the folder and tape two coins on either side of the needle. The added weight will help it sit correctly on the record.
6. To test your record player, open the folder and fit the LP onto the spindle. Adjust the needle so it rests lightly on the record. Place your finger on the smooth part of the vinyl, near the label. Spin the record around clockwise, as smoothly as possible. If the music—especially singing—sounds too high and squeaky, try spinning it slower. If it sounds too low and rumbly, try speeding it up.

Troubleshooting tips and extensions:

• If the folder slides around too much, rest it on a grippy surface, such as a rubber mat.
• If you have trouble turning the record with your finger, take a pencil and press it into the record using the other end as a handle.
• Try different sizes of needles, or change the angle of the needle. Tape the needle in place if you need to.
• Place your record player on top of a box, or lean a box up against the back of the cardboard tone arm, to amplify the sound with resonance.
• Turn your turntable into an instrument by using it to “scratch” a record. (See the story of Grand Wizzard Theodore that follows this project.)

Speaking of Speakers (and Microphones). . .

The radio is even more amazing than the phonograph. Together with two other inventions, the microphone and the speaker, the radio turns sound waves into electricity and then back into sound waves. Today’s synthesizers and electronic audio devices (like the musical greeting cards you circuit bent in Chapter 4) take the conversion process one step further, by converting electrical signals into digital information. But you can still use microphones, speakers, and radios like those invented over a hundred years ago to listen to and transmit music today.

To turn the energy of sound waves into electrical energy, you use the movement of the air to make the amount of electricity flowing through a circuit go up and down. The measure of electrical energy in a circuit is its current. This is how a microphone works. To change electrical energy back into sound waves, you use changes in the current to start air molecules moving. This is how a speaker works. In fact, you can use the same design as either a microphone or a speaker! A device like a microphone or a speaker that can convert one type of energy to another is called a transducer.

The Super-Simple Speaker project in this chapter changes electrical energy to sound energy using a magnet. If you’ve ever played with magnets, you know that they have two poles, positive and negative. Put two magnets together with opposite poles facing each other and they will attract each other. Put both positive or both negative poles together, however, and the magnets will repel, or push each other away.

Now, electricity has an interesting property: whenever it flows, it also creates a magnetic field. An electromagnet is a temporary magnet created by running electricity through a coil of wire or other conductive material. Unlike a permanent magnet, an electromagnet can be turned on and off—it will only attract magnetic materials when the current is flowing. And you can switch the positive and negative and poles on an electromagnet by reversing the direction of the electrical current flowing through it.

Project:
Super-Simple Speaker

All you need to make a speaker is a conductive coil, a strong magnet, and a membrane. You don’t even need batteries! For this Super-Simple Speaker project, all the electrical energy you need comes from the device you’re plugged into. Speakers like this are used in musical greeting cards (like the ones you used in the Circuit Bending project in Chapter 4), earbuds, and other devices where it’s not necessary to get very loud. To produce a louder volume, most speakers include an electric amplifier.

The wire speakers and foil tape speakers in this project both work the same way and can be used in combination. Wire speakers are quicker and easier to make, but foil tape speakers on paper give you more opportunity to get creative. Directions for both are included in the steps that follow.

1. To make a wire speaker, start here. (Skip ahead to Step 4 to make a foil tape speaker on paper.) Take the magnet wire and coil it in a circle or oval using about 20 turns. The coils should be no wider than the width of the tape, but they can be a little longer. One easy way to make these coils is to spread your fingers apart on one hand and wrap the wire around them loosely. Leave about 8 inches (20 cm) of wire hanging loose at the beginning and at the end of the coil. It should be neat, but it doesn’t have to be perfect.
2. Carefully remove the coil from your fingers, keeping the loops lined up. Stick the coil onto a strip of packing tape long enough to fold over and cover the coil completely on both sides. In other words, the wires should be sandwiched inside the layers of tape. Press the two layers together, making them as tight and smooth as possible. The tape is your diaphragm.

   

   

3. Strip the enamel off the ends of the wire by rubbing them with sandpaper. (See the sidebar “How to Strip Wires” earlier.) Then skip to Step 5 to prepare the earbuds.

   

   

4. To make a paper speaker, take an index card and lightly draw a path for your copper foil tape coil to follow. Then stick the copper foil tape right over the pencil line. (See the following sidebar, “Working with Copper Tape.”) The line must begin and end at the edge of the card. (You can even wrap a little of the foil tape over the edge to the other side of the card to make a better connection.) A good design to try is a rectangular spiral. Start the circuit near one of the corners of the card and make a line going up along the edge. At the top of the coil, turn the tape without breaking it. Continue the same way, turning at each corner of the card. Keep going in tighter and tighter square spirals until you reach the center of the card. When you get to the center, you need to make a nonconductive “bridge” so you can bring the foil tape across the outside coils without causing a short circuit. To do that, place a strip of clear plastic tape over the coils you want to cross. Then stick the copper tape to the plastic tape. Bring the end of the foil tape all the way to the edge of the card. (Wrap it around the back a bit if you want.) Your paper circuit is done! Experiment with different designs—any pattern that packs the lines of copper tape closely together without short-circuiting them should work.

   

5. For either the paper or wire version, it’s time to prepare the earbuds. Stereo earbuds usually have one wire connected to a plug that splits into two (one for each ear). Cut the two separate wires about two inches (5 cm) above the split. The remaining piece, with the earphone jack (the metal plug at the end), should be at least 2 feet (60 cm) long.

   

   

6. Strip the ends of each of these two separate wires that you cut off of the left and right earbuds. Inside the plastic housing surrounding each of the thinner wires are several wires that are even thinner. These wires must be separated. Look at them carefully. One of the wires is the ground wire. The other is the wire that brings power to that earbud. The ground wires will probably look the same for both earplugs (in Figure 3-34, both are copper colored). The left and right earbud wires will be two different colors (in the photo, one is red and one is green). Separate the thinner wires inside each earbud wire by color. Strip the ends of both the ground wire (or bundle of wires) and the colored earbud wire or wires. (If you have enamel wires that are twisted together with string-like fibers, like the example in Figure 3-35, you must sand them very carefully. Rub the sandpaper in one direction, from the middle toward the end over and over, instead of rubbing back and forth. Keep going until the bare wire shows through the enamel coating.)

   

   

7. If you are making one mono speaker, take the ground wires from both earbud wires and twist them together. Do the same with the two colored wires. Take one of the twisted bundles of wires. Squeeze or crimp a tiny piece of aluminum foil around the wires as tightly as possible. Do the same with the other twisted bundle. Make sure the two pieces of foil do not touch.
8. If you are making two stereo speakers, wrap each of the ground wires and each of the colored wires separately with a small bit of aluminum foil, the same way you did in Step 7. You will end up with a ground and a colored earbud wire on each branch of your main earphone jack wire.

   

   

   

   

9. Use the alligator clip wires to connect the ground wire to one end of your speaker wire. Connect the colored earbud wire to the other end of your speaker wire. If you want to make a permanent connection to your speaker, twist the speaker wires around the aluminum foil covering the earbud wires and wrap them up with clear or electrical tape. Then separate the ground wires from the colored wires to form a V shape. Sandwich the whole thing in another layer of tape. This will prevent the wires from touching and causing a short circuit. For the paper speakers, you will have to make a big enough V to allow the two sets of wires to reach both ends of the foil circuit. Use clear or electrical tape to connect one set of wires to each end of the copper tape.

   

   

10. Time to test your speaker(s)! Place a magnet over or under the center of your speaker. Insert the earphone jack into your phone, radio, or other device and hold the speaker(s) up to your ear(s). You should hear a faint but recognizable sound coming from the speaker(s). If you don’t hear anything, check all your wires to make sure there are no loose connections.

Extensions: Here are some ways to improve the sound of your speaker:

• Place it inside or on top of a resonator, such as a foam bowl or cardboard canister. If the canister has a steel bottom, you can stick the magnet right to it.
• Try different kinds of magnets, or make a stack of magnets.
• Move the magnets around to different parts of the speaker.
• Make the coil longer (more loops).

Project:
Plain Pencil Microphone

Unlike the magnetic speaker, this primitive microphone uses the sound waves in the air to jiggle a loose piece of conductive material—in this case, the lead in a pencil. (Pencil “lead” is actually graphite, a soft flaky mineral that conducts small amounts of electricity.) This loose piece of pencil lead is a little like a switch that opens and closes a circuit every time it bounces around, varying the amount of electrical current that can flow through. If you send that changing electrical signal to a speaker, it translates those pulses back into sound waves that copy the original sounds you made. This version of a pencil microphone was inspired by a tutorial by YouTube user Dave Hax.

1. To get started, use the knife to carefully carve away a small section on one side of the pencils, in the middle. Keep going until the lead in the center is exposed. The lead should be sticking out above the wood around it.
2. Take the foam cup and poke the pencils straight through, a little below the rim. The pencils should be about 1 inch (2.5 cm) apart. Turn them so the exposed lead is facing up.

   

3. Take a few of the mechanical pencil leads and lay them across the pencils so that they are in contact with the exposed lead.

   

4. Take one of the alligator clip wires and connect it to one of the pencil points. Clip the other end of the wire to the negative terminal on the 9V battery. (You should see “+” and “–” markings on the battery to indicate the positive and negative terminals.)

   

   

5. Take another alligator clip wire and attach it to the positive terminal of the battery. Connect the other end of the wire to the tip of the earphone jack (see “A Note about Earbuds” earlier in this chapter).

   

6. Take the last alligator clip wire and connect it to the ground segment of the earbud jack (the part nearest to the wire). Clip the other end to the point of the other pencil.
7. At this point, your microphone should work. Try talking or singing into it to see if the sound can be heard through the earbuds. Then rest the index card on top of the cup to serve as a diaphragm. See if that makes the microphone sound better.

Extensions:

• Your microphone will pick up some kinds of sounds better than others. High or low frequencies may be harder to hear, and some letter sounds may not be audible. Experiment to see what comes through and what doesn’t.
• Try different materials to make the connection between the pencils, such as a paper clip or a thin nail. Make notes of which materials work best.
• Replace the index card with different kinds of diaphragms to see if you can improve the quality or range of the microphone. For example, try stretching a balloon or piece of plastic wrap across the top of the cup.
• Use speaker wire to extend the distance between the earbuds and the microphone. Clip the alligator clip wires to each of the speaker wire ends, and use additional alligator clip wires at the other end to attach the speaker wire to the earphone jack. Get a helper to go into another room with the earbuds and see if they can still hear you transmitting into the microphone.

Tuning into Radios

Radio waves are a form of electromagnetic energy. They can travel through the air, like sound waves, but they can also travel through the vacuum of space. In fact, some scientists use giant radio telescopes to collect radio waves given off by distant stars.

A radio has an antenna—a metal rod or wire—that picks up the electromagnetic energy and turns it into electrical current. But the antenna picks up radio waves from all the stations in your vicinity (and on good nights, even stations from distant cities). In order to listen to just one station at a time, you need a tuning circuit. Part of this circuit consists of a wire coil. The electricity flowing through the coil creates a magnetic field, just like in a speaker or microphone. A coil or component that stores energy in the form of a magnetic field is called an inductor. Along with the coil, you also need a capacitor. A capacitor stores energy in the form of an electrical field. A variable capacitor lets you adjust the amount of charge it can store. Together, the inductor and the variable capacitor make the tuning circuit resonate at one particular frequency, which amplifies radio waves at that frequency, letting you zero in on the station you want to hear. (A capacitor and an induction coil can also be combined to serve as an oscillator. That’s the device that generates electrical signals with different frequencies in a music synthesizer.)

Once you’ve singled out the frequency you want to hear, you need something to turn the electrical current back into sound waves. The first step is to get them flowing in the right direction. Radio waves make electrons in the circuit flow back and forth, and the high points and low points cancel each other out—a little like the way reflected sound waves merge to create a standing wave. So you need to keep the current from flowing both ways. A diode is an electronic component that only allows electricity to flow in one direction. If you look at the waveform of an electrical current going through a diode, it will appear as if the bottom of the wave has been cut off, leaving only the part from the midpoint up. In early radios, the signal was filtered by sending it through a thin piece of wire, referred to as a cat’s whisker. The cat’s whisker rested lightly on a chunk of mineral such as galena, a type of shiny gray crystal, or even a rusty piece of metal. Radios that run off the energy of the radio waves themselves, and use diodes, raw mineral, or strips of metal to filter their signal, are known as crystal radios.

You now have pulses of voltage that can be used to make an earphone or speaker vibrate and create sound waves in the air.

Since crystal radios use only the energy of the radio waves themselves, you need very sensitive earphones, like piezo earphones, or speakers with electric amplifiers, such as battery-powered speakers, to hear anything. To complete the circuit (remember, electricity only flows when it has a closed circuit to travel along) most crystal radios also need a ground wire. However, the following crystal radio project can work even without a ground wire, making it portable.

Project:
Pizza Box Radio

This home-baked AM radio is a variation on the standard crystal radio. All the components fit in a pizza box, which means it’s portable enough to carry around with you! The secret: the inductor coil also acts as the antenna. This kind of loop antenna radio also works without a ground wire, because the loop itself makes a complete circuit. But because it doesn’t have an outside antenna, this radio works best within a couple of miles of a radio transmitter. For better reception, you can easily hook it up to a ground wire and an antenna.

1. On the pizza box radio, the wire coil is wound around the inside of the box. The rest of the parts are attached to the outside of the box, near the edge where the lid is hinged. Since you will hold the pizza box with the hinge side up, you can call this side the “top” of the radio. The lid and the bottom of the box will become the front and the back of the radio. To get started, put the box down the normal way and open the lid with the hinge away from you. Make sure the cups you are using are shorter than the walls of the box. If they are not, cut them down to size. Use white glue (for paper cups) or hot glue (for plastic cups) to attach the cups to the bottom of the box, near the corners. Leave a little space between the cups and the corners so you have room to wind the wire around them. Make sure the cups are attached securely.

   

2. Before you begin to wind the wire, leave about 1 foot (30cm) of wire hanging loose. Start at the right-hand corner nearest the top of the radio (the lid hinge), and bring the wire down along the right side. Bend the wire around the cup at the right corner nearest you (the bottom of the radio). Continue winding the wire around the cups the same way. Try to keep your coil neat by stacking each level of wire on top of the one before it, but it’s OK if the wires overlap. You can use a few pieces of clear tape to hold the wire in place. Wind about 60 feet (20 m) of wire around the box, ending at the upper left-hand corner. Leave about 1 foot (30 cm) extra at the end of the wire before you cut it.

   

   

3. When you are done with your coil, you will have an extra piece hanging off each end. Feed each end through the opening in the hinge to the lid nearest to its corner (or make your own openings if there aren’t any). Tape the wire down as it leads to the hole. Then poke three small holes through the top of the radio, near the center. The holes should be about 1½ inches (3.75 cm) apart. From the outside of the box, push a brad through one of the holes. Leave a little space between the head of the brad and the cardboard so there will be room to attach wires or clip a test lead. On the inside of the box, bend the legs of the brad to hold it in position. Secure the legs to the cardboard with tape. Repeat with the other two brads. Close the lid. Make sure the lid doesn’t disturb the coil wires.

   

   

   

4. Next, make the capacitor. It consists of two smooth, flat pieces of aluminum foil, with wax paper separating them so they don’t touch. One piece slides over the other. The more they overlap, the higher their capacitance. To start making the capacitor, place a sheet of aluminum foil between two sheets of wax paper. With an iron set on low (no steam), iron the wax paper and foil flat. Take the sandwiched sheets and lay a large paper plate on top of them. Trace around the plate, and add a tab sticking out of the side that is about 2 inches (5 cm) square. Cut out the shape. Then cut both circles in half, so that the tab is also divided in half. Important: Be sure to leave some of the foil on the tab exposed.

   

   

   

5. Now lay one half of the capacitor on the center of the lid. Tape the shape to the box, with the tab sticking out toward the side of the box. Try to keep it as smooth and flat as possible. This will be the lower half of the capacitor. To make the upper half, cut the paper plate you used to trace the capacitor shape in half. With white glue or a glue stick, attach the other half of the foil/wax paper sandwich to the bottom of the plate, matching the edges as much as possible. Tape them together around the edges for extra strength. (Optional: To make the tab on the upper half of the capacitor a little sturdier, back it with some extra cardboard cut from the remaining half of the plate.) With the plate side up, lay the upper half of the capacitor on top of the lower half. Line the two half circles up so the straight edges are matching. Find the middle of this edge and go a little bit down, toward the rounded side. Poke a hole through both halves of the capacitor with a pencil point or other pointy object. The hole should go all the way through the lid of the box as well. Make sure the hole is big enough to allow the upper half of the capacitor to turn easily when you fasten it on with a brad. Then insert a brad through the hole and fasten it on the inside by bending the legs open and taping them to the inside of the lid.
6. Take the two pieces of insulated wire and strip off the insulation at the ends. (Don’t forget that if you are using magnet wire, you need to sand off the enamel to expose the bare copper underneath.) Tape one end to the tab on the lower half of the capacitor so that the bare wire is touching the exposed foil. Bend the wire toward the top of the radio and cover it with tape to hold it in place. Attach the other piece of wire to the tab on the upper half of the capacitor in the same way—but do not tape it to the box!

   

7. Grab one of the free ends of the magnet wire from the coil/antenna sticking out of the holes at the top of the radio. Strip off the enamel insulation by sanding it. Take the capacitor wire that is closest. Twist their bare metal ends together. Then wrap the twisted ends around the nearest brad (not the middle brad). Repeat with the other magnet wire from the coil and the other capacitor wire.

   

   

8. Take the germanium diode and bend the wire near the end with the black stripe around the brad in the middle. Bend the other end around one of the outside brads. Check to see that the diode wire is touching the brad and/or the wires on both ends to make a good electrical connection.
9. The final step is to connect the earphone. Although there is only one ear piece, there are two wires. The electric current flows into one wire, through the earphone, and out the other wire. (It doesn’t matter which.) If there isn’t a lot of bare metal wire sticking out from the earphone wires, you may need to strip the ends. Be careful because they may be made up of multiple strands that are very thin and breakable. If they are, you can twist the multiple strands together to make them a little easier to work with. Wrap one of the earphone wires around the middle brad. Wrap the other wire around the outside brad opposite the diode.

   

10. Your Pizza Box Radio is ready for testing! A loop antenna radio works best when the loop is facing the direction of the radio waves. If you know of a nearby radio transmitter, start by facing in that direction. Place the earphone in your ear and hold the pizza box with the top—the side that has the brads and all the wires connected to it—facing up. It may help to hold the back of the radio against your chest. Place one hand on the capacitor. Slowly turn the upper piece of the capacitor like a dial and try to tune in a station. Chances are, if you find one, it will be very faint. If you do find one, mark it with a pencil. If you want to look for more, or if you don’t get a clear signal on the first station, turn the capacitor a little and try fiddling with the capacitor dial again.