Introduction: Simple Loudspeaker
This loudspeaker design consists of a plastic tub with lid, a screw, a wire, a magnet, and tape that when plugged into a stereo speaker output, generates sound and student enthusiasm. This activity illustrates electricity and magnetism phenomena by providing an example of the interaction between a current carrying wire and a magnet. The learner objective is that by building a simple loudspeaker, students will be able to evaluate an electromagnetic technology and explain that the goal of technology is to provide solutions to practical problems.
Step 1: Step 1: Gather Materials
• Plastic container with lid (8oz container)
• Wood screw (a bit longer than the tub height)
• 2 meters of insulated wire (24 gauge)
• One small permanent magnet
• Wire stripper and cutter
For testing the speaker
• 1.5-V battery (AA or A)
• Sound signal source (e.g.,boom box or a radio receiver/amplifier with separate ground and signal connections to the speaker outputs)
• 4- to 6 ohm resistor
I used an old pringle container taht was cut to fit the screw size I used.
Step 2: Step 2: Construct Electromagnet
Strip about 2 cm of insulation from each end of the wire. Near the head of the screw, wind the wire around for at least 50 turns, leaving about 45 cm of unwound wire at each end.
Step 3: Step 3: Construct Speaker Base
Screw the electromagnet into the middle of the inside of the plastic tub until the head of the screw is just
below the level of the top rim of the tub. Punch two additional small holes in the bottomof the tub. Stick the ends of the wire through these holes so they come out the back.
Step 4: Step 4: Construct Speaker Diaphragm
Tape the magnet to the middle of the lid (either insideor outside) and put the lid on the tub. The screw head should be close to, but not touching, the magnet or the lid. The ends of the wires from theelectromagnet will be connected to the output of the boom box or other
Step 5: Step 5: Test Speaker (Battery Test)
Using the 1.5-V battery with the loudspeaker, briefly connect the ends of the coil wires to the battery terminals. (One student lightly taps one battery connection on and off while her partner lightly touches the top of the lid or listens to the speaker close to her ear.) Students
feel and hear a light tapping as the battery connection is alternately made and broken. They might also be able to see the lid moving.
Step 6: Step 6: Test Speaker (Stereo Test)
Connect the ends of the wire to the speaker output of the signal source (stereo). Connect the resistor to electromagnet. Use the amplified output of the boom box (the earphone output will not supply sufficient power). Turn on the signal source and listen.
Step 7: Step 7: Have Students Explain Function of Loudspeaker
After construction of the loudspeaker, students must then explain in a written assignment or instructor interview how the loudspeaker works using the electricity and magnetism concepts studied in class.