How Loud Can Paper Speakers Get?
|Areas of Science||
Technology of Art
Science With Your Smartphone
|Time Required||Average (6-10 days)|
|Material Availability||Specialty electronics materials required. See the Materials list for details.|
|Cost||Average ($40 - $80)|
If you like listening to music and making crafts, this is a great project for you. You will learn how to make a completely functional speaker that you can use to listen to real music...out of paper! Along the way, you will learn about the science behind how a speaker works. Speakers depend on magnets to create sound—does adding more magnets make the sound louder? Try this project to find out!
This project is compatible with Google's Science Journal app, which allows you to collect data using your smartphone.
Measure how the number of magnets affects the loudness of a paper speaker.
The speaker design in this project was inspired by this page: http://makezine.com/projects/styrofoam-plate-speaker/.
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Last edit date: 2018-06-30
What do you use to listen to music? Do you use a pair of headphones connected to a smartphone, or maybe a pair of speakers connected to a stereo? From the tiniest pair of headphones to the largest home-theater surround sound systems, most speakers have something in common. They rely on magnets to generate sound. In fact, speakers actually have two different types of magnets. They have permanent magnets, or special metals that are always magnetic, and electromagnets, or coils of wire that are only magnetic when an alternating current flows through them. Are some of these terms new to you? You can read more about them in the Science Buddies Electricity, Magnetism, & Electromagnetism Tutorial.
So, how exactly do speakers convert a song stored on your computer or a streaming music service to sounds that your ear can hear? Your computer, smartphone, or other audio device converts the song file into an electrical signal. That signal is sent to a coil of wire in the speaker, which generates a magnetic field. That coil is wrapped around a permanent magnet, which has its own magnetic field. These two magnetic fields push on each other, or exert a force. This force causes the speaker cone to vibrate, and push on the air molecules next to the speaker. This vibration travels through the air as a sound wave and is detected by your ear. The sound wave has a frequency, measured in hertz (Hz). "High-pitched" sounds, like a child's voice or a tiny bell, have a higher frequency, and "low-pitched" sounds, like an adult's voice or a bass drum, have a lower frequency. Figure 1 shows a simplified diagram of the system. See the HowStuffWorks reference in the Bibliography for a more detailed explanation.
Figure 1. Simplified diagram of a speaker, including the input (electrical signal) and the output (sound waves).
Several factors can affect the strength of a magnetic field. The number of turns of wire in a coil and the amount of current flowing through the coil can affect the strength of a temporary magnet. The size, shape, and material of a permanent magnet can all affect its strength. In this project you will use a stack of small permanent magnets instead of a single large magnet—this will allow you to test different numbers of magnets. Do you think adding more magnets will make the speaker louder?
In order to determine the volume or "loudness" of the speaker in a scientific manner, you will need to measure the sound pressure level, which is measured in decibels. Technically, this unit is referred to as dBSPL, because "dB" on its own can have different meanings depending on the context (for example, the strength of an electrical signal instead of a sound wave). However, in the context of an audio project, many sources just refer to "decibels," abbreviated "dB," so we will use that convention in this project. See the Physics Classroom reference in the Bibliography to learn more about the decibel scale used for measuring sound.
Terms and Concepts
- Permanent magnet
- Alternating current
- Magnetic field
- Speaker cone
- Sound wave
- Hertz (Hz)
- Sound pressure level
- How does a speaker work?
- What factors affect the strength of an electromagnet?
- What factors affect the strength of a permanent magnet?
- Will adding more permanent magnets to a speaker make the sound louder?
- Finio, B. and De Brabandere, S. (2015, March 14). Electricity, Magnetism, & Electromagnetism Tutorial. Retrieved September 25, 2015 from http://www.sciencebuddies.org/science-fair-projects/electricity-magnetism-electromagnetism-tutorial
- Harris, T. (n.d.). How Speakers Work. HowStuffWorks. Retrieved September 25, 2015 from http://electronics.howstuffworks.com/speaker1.htm
- Henderson, T. (n.d.). Intensity and the Decibel Scale. The Physics Classroom. Retrieved September 25, 2015 from http://www.physicsclassroom.com/class/sound/Lesson-2/Intensity-and-the-Decibel-Scale
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Materials and Equipment
To do this project, you will need these electronic parts from Jameco Electronics:
- Neodymium magnets, also called rare earth magnets, 12 mm x 3 mm each (6 pack), part #2181327
- Magnet wire (one spool of 30 gauge wire), part #2119363
- 12 V, 2 A DC wall adapter, part #380156
- 3.5 mm stereo plug to male RCA plug cable, part #228401
You will also need the following materials:
- Paper (1 sheet)
- Clear tape
- Paper plate; the project will also work with other materials (plastic or foam) and other shapes (like bowls or cups).
- Business cards (3)
- Piece of cardboard, about the size of your paper plate (it can be rectangular, it does not have to be round)
- Small piece of fine-grit sandpaper
- Craft glue
- Double-sided foam tape
- Optional: Colored markers or pencils for decorating your speaker
- Lab notebook
- Mini audio amplifier, available from Amazon.com.
- A smartphone or tablet to record your data
This project uses Google's Science Journal app, a free app that allows you to gather and record data with a cell phone or tablet. You can download the app from Google Play for Android devices (version 4.4 or newer) or from the App Store for iOS devices (iOS 9.3 or newer).
- The phone must have a 3.5 mm "headphone" jack.
- If you do not have access to a smartphone that can run Google's Science Journal app, you can purchase a sound level meter from Amazon.com.
- A way to play audio tones on your smartphone or computer. Note that if your phone cannot play the tones in the background while you run the Google Science Journal app, you will need a second phone or computer (one to play the tones and one to run Google Science Journal). There are several different ways to do this:
Safety Notes about Neodymium Magnets:
- Handle magnets carefully. Neodymium magnets (used in this science project) are strongly attracted and snap together quickly. Keep fingers and other body parts clear to avoid getting severely pinched.
- Keep magnets away from electronics. The strong magnetic fields of neodymium magnets can erase magnetic media like credit cards, magnetic I.D. cards, and video tapes. It can also damage electronics like TVs, VCRs, computer monitors, and other CRT displays.
- Keep magnets away from young children and pets. These small magnets pose a choking hazard and can cause internal damage if swallowed.
- Avoid use around people with pacemakers. The strong magnetic field of neodymium magnets can disrupt the operation of pacemakers and similar medical devices. Never use neodymium magnets near persons with these devices.
- Use the magnets gently. Neodymium magnets are more brittle than other types of magnets and can crack or chip. Do not try to machine (cut) them. To reduce the chance of chipping, avoid slamming them together. Eye protection should be worn if you are snapping them together at high speeds, as small shards may be launched at high speeds. Do not burn them; burning will create toxic fumes.
- Be patient when separating the magnets. If you need to separate neodymium magnets, they can usually be separated by hand, one at a time, by sliding the end magnet off the stack. If you cannot separate them this way, try using the edge of a table or a countertop. Place the magnets on a tabletop with one of the magnets hanging over the edge. Then, using your body weight, hold the stack of magnets on the table and push down with the palm of your hand on the magnet hanging over the edge. With a little work and practice, you should be able to slide the magnets apart. Just be careful that they do not snap back together, pinching you, once you have separated them.
- Wear eye protection. Neodymium magnets are brittle and may crack or shatter if they slam together, possibly launching magnet fragments at high speeds.
Building Your Paper Speaker
- In this section, you will assemble your paper speaker. Figure 2 shows a "cross section" of the speaker assembly. Refer to this diagram as you follow the assembly steps.
Figure 2. A cross-section diagram of the paper speaker. The speaker "cone" is made from a paper plate. This plate is supported by two business cards folded into "M" shapes, which are attached to a piece of cardboard as a base. A coil of wire is attached to the underside of the paper plate. This coil fits around a stack of magnets, which sit on top of the cardboard base. The magnets and the coil are not physically connected to each other; this allows the coil to move back and forth, generating vibrations that turn into sound waves.
- Optional: Before you start, you can use markers to decorate the front of your paper plate, like the one in Figure 3.
Figure 3. A decorated paper plate.
- Cut two strips of paper, about as wide as the height of your stack of magnets (roughly 2 cm) and about 20 cm long, as shown in Figure 4.
Figure 4. Two strips of paper, roughly 2x20 cm each.
- Wrap one strip of paper tightly around the stack of magnets, as shown in Figure 5. Secure it with a piece of tape so it does not unravel.
Figure 5. One strip of paper wrapped around the stack of magnets.
- Wrap the second strip of paper around the first one, as shown in Figure 6. Use a piece of tape to secure the second strip to prevent it from unraveling. Do not tape the two strips of paper to each other.
Figure 6. Second strip of paper wrapped around first paper wrapping and the stack of magnets.
- Slide the stack of magnets and inner paper tube out from the outer paper tube. You should now have two paper tubes, one with a slightly larger diameter, and your stack of magnets, as shown in Figure 7.
Figure 7. Stack of magnets next to the two paper tubes.
- Make sure that the stack of magnets fits inside the larger tube, with a gap in between them, as shown in Figure 8. You can discard the smaller paper tube; it was only used as a spacer to build the larger tube, and you do not need it to build your speaker. The magnets need to be able to slide back and forth inside the larger tube without touching the walls. If the tube is too tight, you may need to loosen it (undo the tape, let it unravel slightly, then re-tape it), or make a new one using a thicker "inner" tube as a spacer.
Figure 8. Magnets inside the larger paper tube. Notice the gap between the magnets and the tube.
- Put the magnets inside the larger paper tube. This will help the tube hold its shape so you do not accidentally crush it while handling it.
- Pull about 20–30 cm of wire out of the spool of magnet wire. Now use a small piece of tape to attach the magnet wire to the paper tube, as shown in Figure 9. Do not tape the end; rather, make sure you leave the 20–30 cm of wire dangling past the piece of tape. Do not cut the wire yet.
Figure 9. Magnet wire taped to the paper tube.
- Leaving the 20–30 cm of wire alone, carefully and neatly wrap 50 turns of the wire still attached to the spool around the paper tube, as shown in Figure 10. Make sure the turns of wire are tight against each other and against the tube, not loose and tangled. Keep the magnets inside the tube while you do the wrapping—this will prevent you from crushing it.
Figure 10. 50 turns of wire wrapped around the tube.
- Completely wrap tape around the wire coil to prevent it from unraveling, as shown in Figure 11.
Figure 11. Tape wrapped around the wire coil to secure it.
- Cut the end of the wire still attached to the spool so it is about the same length as the first end, roughly 20–30 cm, as shown in Figure 12. Now remove the magnets from the tube.
Figure 12. Wire coil with both ends of the wire cut.
- Use a small piece of fine-grit sandpaper to sand the insulation off both ends of the wire, as shown in Figure 13. Refer to the Science Buddies Wire Stripping Tutorial for an instructional video on how to strip magnet wire.
Figure 13. Stripping magnet wire with sandpaper.
- Fold two business cards into "M" shapes. When standing on their sides, the business cards should be slightly taller than your paper tube, as shown in Figure 14. This is important so the wire coil has enough room to move up and down without hitting the base of your speaker (refer back to Figure 2, notice how there is a gap between the bottom of the paper tube and the cardboard base).
Figure 14. Two business cards folded into "M" shapes, slightly taller than the paper tube when standing on their sides.
- Turn your paper plate upside-down so the decorated side is facing your work surface. Glue the paper tube and business cards to the back of the plate, as shown in Figure 15. The paper tube should be in the center of the plate, and the business cards should be to either side of it. The exact distance does not matter, as long as they are not close enough to bump into the tube. Wait for the glue to dry completely before you proceed to the next step.
Figure 15. Business cards and paper tube glued to the back of the paper plate.
- Glue the free ends of the business cards to a cardboard base, as shown in Figure 16. Do not glue the paper tube to the cardboard base. The wire coil needs to be free to move up and down so your speaker can vibrate. Wait for the glue to dry completely before you proceed to the next step.
Figure 16. Business cards glued to the cardboard base (bottom of the picture).
- Cut a circular piece of double-sided foam tape about the same size as one of your magnets. Use it to stick the stack of magnets to the center of a business card, as shown in Figure 17.
Figure 17. Stack of magnets stuck to a business card with double-sided foam tape.
- Gently pull the paper plate and the cardboard base away from each other, far enough that you can slip the stack of magnets underneath the paper tube. Line the magnets up with the inside of the paper tube, then let the plate come back down, so the wire coil surrounds the magnets, as shown in Figure 18. Do not glue or tape the business card to the cardboard base; this will allow you to easily remove it to change the number of magnets during the experiment.
Figure 18. Magnets inserted into the wire coil.
- You are finished building your paper speaker. In the next section, you will connect it to an audio device and an amplifier.
Figure 19. A completed paper speaker.
Connecting Your Audio Device and Amplifier
- Connect your smartphone (or other device that you will use to play the audio tones), amplifier, and paper speaker, as shown in Figures 20–23.
- Insert the 3.5 mm plug from your audio cable into the "headphone" jack on your smartphone.
- Insert the RCA plugs (the red and white plugs on your audio cable) into the "Input" jacks on the back of the amplifier.
- Insert the stripped wires from your paper speaker coil into the "R+" and "R-" speaker terminals on the back of the amplifier (you can use "L+" and "L-" instead, but do not mix "L" and "R" or your speaker will not work). These terminals have small red and black tabs beneath them. To insert the wire, push down on the tab, push the wire into the hole in the terminal, then release the tab. The tab will spring back up and grip the wire so it does not fall out.
- Insert the barrel plug from your 12 V adapter into the "DC 12V" jack on the back of the amplifier.
- Important: Make sure the volume knob on the amplifier is turned down (all the way to the left). This will prevent any loud sounds from playing the moment you plug in the power.
- Plug the other end of the 12 V adapter into a wall outlet.
Figure 20. A diagram of all the connections between the smartphone, amplifier, and speaker.
Figure 21. 3.5 mm audio cable plugged into a smartphone's headphone jack.
Figure 22. Picture of the back of the amplifier with RCA plugs, speaker coil wires, and 12 V adapter barrel plug all connected.
Figure 23. A completed paper speaker setup with amplifier and smartphone.
Testing Your Paper Speaker
- Double-check to make sure the volume on the amplifier is turned down all the way (turn the volume knob all the way to the left).
- Push in the "Power" button to turn the amplifier on.
- Play some music on your smartphone.
- Slowly turn the volume knob on the amplifier up until you can hear the music. Adjust the volume to a comfortable level. You can also adjust the "bass" and "treble" knobs on the amplifier to adjust how the music sounds. The bass knob will control the deeper sounds, and the treble knob will control the higher sounds.
- If you do not hear music at all, double-check that you made all the connections properly, as shown in Figure 20. Make sure you sanded the insulation off the ends of the wire coil in your speaker, and that the ends of the wires are secure in the speaker terminals on the amplifier. If you did not properly sand off the insulation, or if the wires are not secure in the terminals, your speaker will not work.
Collecting Your Data
- Create a data table like Table 1 in your lab notebook.
|# of Magnets||Trial 1||Trial 2||Trial 3||Average|
- Set up your experiment in a quiet room, where there are no other sources of noise, like people talking or traffic.
- Make sure you have a way to play a 1,000 Hz test tone. You can use an online tone generator, search for a tone generator app on your phone, or download a .wav file from this Science Buddies page.
- Note: You might be wondering "Why 1,000 Hz?" Most paper speakers will be "good" at playing sounds around this frequency, but you could use a different frequency if you wanted to. The point of using a single test tone is that its volume will not change, unlike a song, which may have louder parts and quieter parts. To learn more about how paper speakers respond to different frequencies, see the Variations section.
- Place your phone a fixed distance from your paper speaker. It is important to keep this distance constant throughout the experiment, because sounds will get quieter as you get farther away from the source (meaning the decibel level will decrease). Moving the phone will affect your measurements.
- Open the Science Journal app and select the sound sensor. To learn how to use the Science Journal app and how to use the sound sensor, you can review the relevant tutorials on this Science Journal tutorial page.
- Sit perfectly still and take a sound intensity reading with the app. This reading will measure the level of "background noise" in the room.
- The microphone on your phone is very sensitive, so something as simple as fidgeting in your chair, scratching your head or tapping a pencil on the table can cause the reading to change. Make sure you sit still and eliminate other sources of noise.
- Even if it is very quiet, the reading will not be zero dB. For example, a quiet library is typically about 30 dB. Refer back to the Physics Classroom reference in the Bibliography if you need a reminder about how the decibel scale works.
- Even if you do your best to sit still and eliminate other sources of noise, the sound reading may still bounce around by a few decibels. If this occurs, record data for several seconds, and the app will automatically calculate an average value..
- Now, play a 1,000 Hz tone. Obviously, you will have to move and make some noise to operate the device—this is okay, as long as you sit still again when you take a sound level reading. If you are using the same smartphone to play the tone and measure the sound level, remember not to move it; it needs to stay a fixed distance from the speaker.
- Record the sound level, in decibels, in your data table, under "Trial 1" in the row for six magnets. Again, if the reading fluctuates slightly, take an average reading over a period of a few seconds.
- Repeat steps 6–7 two more times, for a total of three trials with six magnets.
- Now, remove one magnet from the stack of magnets. Do this by lifting the paper plate and sliding out the business card with the magnet taped to it. The magnets are very strong, so you may need an adult to help you slide a single magnet off the top of the stack.
- Note: As you remove magnets from the stack, you will need to add one or more pieces of double-sided foam tape as "spacers" to the bottom of the stack of magnets, as shown in Figure 24 (exactly how many pieces depends on the thickness of your tape). This ensures the magnets remain centered in the wire coil where the magnetic field is the strongest. If you never add more spacers and only remove magnets from the top of the stack, eventually the magnets will be near the edges of the coil, where the magnetic field is weaker, and this will affect your results.
Figure 24. As you remove magnets from the stack, use additional pieces of double-sided foam tape as spacers to keep the remaining magnets centered in the coil.
- Re-insert the magnets into the paper speaker.
- Repeat steps 6–10 five more times (with five, four, three, two, and one magnets). Make sure you do three trials for each number of magnets, and add double-sided foam tape, as necessary, to keep the magnets centered in the coil.
- For each number of magnets, calculate an average volume, in decibels, and record this value in your data table.
- Analyze your results.
- Make a graph with average volume, in decibels, on the y-axis and number of magnets on the x-axis. Include a line on the graph that shows the background noise level in decibels (you recorded this value in step 5).
- How does the volume, in decibels, change with the number of magnets?
- Do your results match your predictions?
If you like this project, you might enjoy exploring these related careers:
- In this project, you varied the strength of the magnetic field by changing the number of permanent magnets. What if you make changes to the wire coil instead? What happens if you change the number of turns of wire, the diameter of the coil, or the length of the coil? Build several different speakers with different coils and repeat the experiment with each speaker. How do the results change?
- Turn this into an engineering design project to see if you can design and build the "best" speaker. How will you define your criteria for the "best" speaker? Is volume all that matters, or do you also care about sound quality? For example, what material and shape works best for the speaker cone? Does a plastic cup work better than a paper plate? What about changing the materials you use for the support structure? Does something else work better than cardboard and business cards?
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