Engineering Outreach: "How a Speaker Works"

I. Overview

Project Abstract:

• "In this activity, students will learn how electromagnetism and vibrations can be used to produce sound.  The students will learn that current, when run through a coil, can produce a magnetic field.  Students will also learn how vibrations can be used to produce sound, and how volume and pitch can be altered.  Students will build their own speaker by making electromagnetic coils and amplification chambers.  They will make the speakers by using different numbers of magnets and coils to vary the volume.  They will construct amplification chambers out of cardboard and experiment with different sizes and shapes.  In this way, students will learn how the physical properties of a speaker change the volume of the sound."

Prototyping a Speaker:

• What we have constructed is a clear plastic speaker on the laser cutter in the Materials Science department lab. With this premade, functional speaker, we can show how easy this experiment is while introducing it. While the children will construct their own speakers in the process, they can see the light at the end of the tunnell with the plastic speaker we have provided. A picture of the plastic speaker is on the right.

II. How to Conduct Experiment

Materials:

• The main component of this experiment is the actual stero. Instead of dissecting a complex stereo, some are equipped with multiple output speaker jacks in the back of the unit. A constructed speaker can easily be wired into the stereo with these jacks.
• Other materials include: thin covered wire, magnets, and probably some tape (electrical preferably).
• The speakers that will be built in this activity can be built out of almost anything. The material we chose was cardboard.
• It is also suggested to include some out of the ordinary materials for the speakers. We actually had great success with a red Solo cup.

Procedure:

• Ideally, an actual speaker should be shown first to demonstrate what a working speaker looks like.
• Next, speaker construction can begin. There is a lot of freedom in this part of the exercise. Any geometry will work, although some are better than others. This is really where the lesson comes in.
• Once the geometry of the speakers is complete, a coil of wire must be wrapped and taped together. This wire will attach to the back of the stereo.
• Next the magnet can be placed inside of the wire coil and the wire can be connected. The wire will vibrate, thus causing sound against the hard surface of the speaker. Shown on the right is the set-up of the back of a constructed speaker. The speaker used in the picture is a red Solo cup.
• Once the stereo is turned on the speaker should emit sound. The sound properties will be dependant on the geometry and material of the speaker you have constructed.

II. What We Have Learned

Science & Engineering Aspects:

• What we have just created is an electromagnet, a complex physics concept.
• The sounds coming from the speakers are clearly vibrations. This provides a great lesson in how sound works.
• The construction of the speaker itself plays a role in the properties of the outgoing sound.

What kids can take from the lesson:

• Science can be fun! A working, functional speaker made out of simple objects is pretty cool.
• This phenomena that is a speaker is easy to visualize. It can make kids feel smarter and more powerful. Being able to understand how something complex like a speaker works will be good for the kids.

<Jono Matusky, Dave O'Connor, Justin Yi, Shrey Aggarwall>
Carnegie Mellon University
May 1, 2009