Introduction: Homemade Speaker for Under $4

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About: When it comes to DIY, the more the merrier!

These days it seems speakers are always on sale. Even though the sales might be good, the price points will probably never come close to that of this inexpensive DIY speaker. Other than magnets and maybe the aux connector, all of the components can be salvaged from the average household.

I researched and designed this speaker workshop more or less by reading other instructables and watching youtube how to's. It was intended for a workshop setting, so I bought the components in bulk. In this workshop, I taught speaker fundamentals and also instilled in the participants the realization that loud speakers are expensive for a reason.

This speaker is compatible with aux devices and the sound coming out is mono. If you want stereo sound, just build two of them and solder up the aux cable to both.

Step 1: DIY Speaker Theory

The speaker connects to the audio device through the auxiliary port, a.k.a. the aux port. Electric signals come out of the audio device will normally go into some sort of amplifier circuit. However, in this case, we have no amplifier as this speaker is bare bones.

The signals travel directly into the speaker coil. When electrical current flows through a wire coil, it produces a magnetic field according to Lenz's Law. The image showing the right hand rule of Lenz's Law is taken from this explanation.

Near the speaker coil is a permanent magnet. The magnetic field from this permanent magnet interacts with the speaker coil's induced magnetic field. The two magnetic fields might attract or repel, depending on their relative orientation. Thus, the speaker coil and magnet might try to move closer or further away from each other.

Since the audio signal is AC, the speaker coil and permanent magnet attract and repel each other in rapid succession, depending on the direction of the current in the speaker coil.

If you attach the speaker cone material to either the wire or the permanent magnet, it is moved back and forth corresponding with the changing AC current. Usually, the cone is attached to the coil as it's lighter and thus moves faster.

The cone's oscillations are fast enough to be considered vibration. This vibration produces the sound one hears from the speaker. The second diagram attached is from this speaker repair website. It is an exploded view that may help visualize how a speaker works.

Step 2: BOM and Required Tools

This materials purchased for this workshop were enough to supply the parts for 40 speakers. Thus, I bought about $160 worth of materials. The materials list is simple and is described below. Additionally, I will detail out the tools required for this workshop. The workshop can be finished in under an hour.

Speaker Cone

  • Styrofoam plates
    • They are disposable and cheap
    • This cone material is better at producing base sounds
      • Choosing different speaker cone material will work better with different frequency sounds
  • Cost 10 cents/speaker

Speaker Coil

  • 28 gauge magnet wire
    • Make sure it's magnet wire (coated or enameled) so that the coil does not short itself
  • Printer paper
    • To give students something to construct the wire coil around
  • Cost 45 cents/speaker
    • Participants did not use near the amount of wire I purchased though, so this is a high number

Permanent Magnet

  • Neodymium Disc Magnets (axially polarized)
    • I gave students 8 individual magnets to make a magnetic cylinder about 1/2" OD x 1/2" height
    • Purchased from good old ebay.com
    • Be sure to treat them with care as they are fragile
  • Cost $1.65/speaker

Base Material

  • Chipboard
    • Participants were given a 4.5" x 7" sheet
    • I chose chipboard because it has some stiffness but is still lightweight and thin
  • Cost 25 cents/speaker

Aux Connector

  • Aux cord with male 3.5 mm jacks on each end
    • I found the cheapest way was to buy a short aux cord and cut it in half
  • Cost $1.50/speaker

Cone Support

  • Business card stock
    • Like a baby whose head is too heavy, use this stiff card stock to hold the Styrofoam plate up. More on this in the next step

Required Tools

  • General tools to work with wires
    • Soldering iron, solder, flux, wire strippers, wet sponge
    • Electrical tape
    • Multimeter
    • OPTIONAL: Lighter
      • To burn off the insulation on the fine wires in the aux and burn off coating on magnet wire
  • Colored marker and ruler
    • To measure important dimensions on the speaker
  • Hot glue gun
  • Scissors
  • Needle nose pliers

Attachments

Step 3: Make the Speaker Cone

This step is the most important step! Fortunately, it is still pretty easy.

  1. Cut two strips of paper to 0.75" x 4"
    1. Color one with the marker
  2. Connect the magnets together to form one longer cylinder
    1. Be careful, the neodymium magnets are brittle and can easily break
  3. Wrap the blue strip around the magnet cylinder and tape it off
    1. This paper's ultimate purpose is to ensure a slip fit between the speaker coil and the magnet cylinder
      1. When magnetic field are close, they have a greater effect on each other. Keeping the coil's induced magnetic field close to the permanent magnet will enable the speaker to be louder
  4. Wrap the white strip around the blue cylinder and tape that off as well
    1. This creates two concentric cylinders, as shown in the first image
  5. Wrap outer white paper cylinder in as many turns as you feel
    1. I targeted about 100 turns
      1. Adding turns will increase the impedance of the speaker
      2. Check out this impedance explanation
      3. Try to evenly space out the turns of the wire along the cylinder
    2. Be sure to leave about 2" of excess wire on either end, these will be the exposed leads
  6. Using the hot glue, lock the wire coil in place
    1. Use enough hot glue to ensure the wire does not unravel
    2. Using too much hot glue adds weight to the speaker coil, which damps its motion. Damped motion means there will be lower amplitudes of motion, which means your speaker will not be as loud
  7. Strip 1" of the coating off of the magnet wire's leads
    1. Use fire for the easiest method, I like to use a lighter to burn it off
      1. Be sure you don't catch the paper on fire!
    2. Alternately you could use scissors to gingerly scrape it off
  8. Remove the magnet slug
  9. Remove the inner colored strip of paper with the needle nose pliers
    1. This enables the wire coil to slide nicely around the magnet cylinder without too much friction
  10. Trim away excess paper on the top and bottom half of the speaker coil

Step 4: Prepare Base and Speaker Cone

This step is very simple and will take no time at all

  1. Define center on both the plate and the chipboard base using the ruler and marker
  2. Hot glue the magnets to the chipboard.
    1. Do not let the hot glue go above the very base of the cylinder, as it will damp the vibration of the speaker cone and make it lower quality.
  3. Cut three strips of paper about 1" wide and about 5" long. Bend them into a zigzag shape
    1. These will support the cone and keep it standing up
  4. Hot glue the zig zags to the plate in the triangular pattern as shown in the third image.

Step 5: Prepare Aux Cord

  1. Cut the aux cord in half
  2. Strip one end so the interior three wires are exposed
  3. Strip those three interior wires
    1. One is ground, two are signal
      1. Depending on your aux cord manufacturer their colors will change
    2. Use a multimeter to find this out
  4. Connect the ground wire to one lead of your speaker coil by twisting them together
  5. Connect one signal wire (your choice does not really matter) to the other speaker coil lead
  6. Solder the connections and cover them in electrical tape for strength
    1. Test your speaker coil using a multimeter on the continuity test setting on the 3.5 mm jack
      1. If there is a connection, the solder job worked!
      2. You can also measure the impedance of your speaker at the multimeter using its DC ohmmeter
  7. The leftover signal wire should be covered in electrical tape and will not be used
    1. This would be used to establish stereo sound with a second speaker if you want.
      1. If you do this, the ground wire would have to become a ground node between the two speaker coils and the aux ground wire

Step 6: Test Your Speaker

At this point you want to test your speaker.

  1. Place the speaker coil around the permanent magnet
  2. Place a small piece of paper on top of the coil
    1. If the device works, you will see this piece of paper vibrate or fall off
  3. Plug the aux into your audio device and play a song of your choice
  4. If the paper indicates the speaker is working, move on!
    1. If the paper does not vibrate off, then check your solder job and that the paper cylinder can easily move around the magnet slug

Step 7: Attach Speaker Coil to Cone

As the last step, attach the speaker cone to the speaker coil using hot glue.

  1. Use hot glue to glue the coil to the center of the plate
    1. Try to use minimal glue to keep weight down
  2. Flip over the speaker cone so the plate faces up
  3. Place the coil around the permanent magnet, completing the speaker
    1. OPTIONAL: hot glue the bottom of the zig-zag standoffs to attach the speaker cone to the base
  4. Test out your speaker!

Advantages:

  • Low cost
  • A low time investment workshop
  • Lots of room to play with the speaker and try to perfect it

Disadvantages:

  • The speaker is not loud
  • The speaker is fragile and not easy to carry around
  • It looks like crap

Areas to Improve On:

  • Maybe add in some sort of amplifier to get more sound out of the system
  • Find a better low cost speaker cone material that would create more sound
  • Use solid permanent magnet instead of small cylindrical ones to get a stronger permanent magnet
  • Create a better way of keeping speaker coil concentric with permanent magnet so that there is less friction

It anyone reading this sees some flaws with this instructable, please point them out! I will make the changes as soon as I see them.