Engineering Speakers

Students focus on one part of a communication system—the decoder—as they apply scientific knowledge about magnetic fields and electromagnets to design speakers.

• Speakers work by applying the rules of magnetism.
• A speaker is a decoder that uses magnetism to turn electrical energy into sound energy.
• The parts of a speaker work together to turn electrical energy into sound energy, which is carried in vibrations that we hear as sound.

• What technologies have speakers?
• Why do speakers function with two magnets?
• Why do speakers need one electromagnet and one permanent magnet?
• How does electricity pass through an electromagnet?
• How can electromagnets be made stronger?
• Why do all speakers have a cone?
• What determines a speaker’s volume?

Misconception: Radio waves are not related to light at all.

Fact: Radio waves are the longest form of electromagnetic waves, so they are similar to visible light, which is the light we see. The difference is that radio waves carry less energy.

Misconception: Light cannot be used to send information through a communication system.

Fact: Many communication systems use light signals sent through fiber-optic cables. 

Attract : to pull toward

Circuit : the circular path that electrons travel in a negative to positive direction

Electricity : the flow of electrons through a conductor

Electromagnet : a tightly wound coil of wire that produces a magnetic field when electricity passes through the wire

Magnet : an object that produces a magnetic field

Magnetic field : the invisible area around a magnet that attracts or repels other magnets and magnetic materials such as iron

Permanent magnet : a magnet that stays magnetized without electricity

Repel : to push away

Speaker : a device that uses magnetism to transform electrical energy into sound energy

A Radio Broadcast

When Emily Ross was a college student, she volunteered as a DJ at her college radio station. Every Monday from 3 pm to 5 pm, she took to the airways. She would broadcast a wide range of musical styles from the station.

Radio stations are part of a communication system that can send information across a wide distance. This information includes songs, breaking news updates, and weather reports. As a DJ, Emily was the source. She sent information to listeners to the station. When Emily spoke into a microphone, the microphone encoded the sound of her voice into signals that could be transmitted.

Radio Waves

Radio stations transmit sounds because they send out radio waves. Radio waves are a form of light energy. There are different types of light, and the type of light energy depends on the amount of energy in the different waves.

Scientists organize the different wavelengths of light on an electromagnetic spectrum. The range of light waves that humans can see is called visible light. It is in the middle of this spectrum. Radio waves, which are sent out by radio stations and captured by your radio, have the lowest energy. Microwaves are used in appliances to heat up your food. They are also used in satellites for communication and navigation. X-rays are used at the dentist to capture images of teeth and at the airport to see through bags.

How Radio Stations Send Information

All radio stations have a radio tower. This tower transmits a certain frequency of radio wave across a wide distance. Radios within range of the waves and are tuned to the frequency will play the sounds that are being broadcasted. A radio is a device that transmits and/or receives radio waves.

Once a radio picks up a radio wave, it converts the information into electrical signals. Those signals are then decoded by a speaker. A speaker is a device that uses magnetism to transform electrical energy into sound energy. Speakers are decoders because they convert electrical signals, which we cannot hear, into sound waves, which we can hear. Radios, televisions, cell phones, and headphones all use speakers.

How Magnets Work

Understanding how speakers work begins with the basic rules of magnetism. Magnets are objects that produce a magnetic field. A magnetic field is the invisible area around a magnet that attracts or repels other magnets and magnetic materials such as iron. To repel means to push away. To attract means to pull toward.

All magnets have a north pole and a south pole. The north pole of one magnet always attracts the south pole of another. However, two north poles will always repel each other. Two south poles will also repel each other.

One of the reasons that magnets are so useful is that they can attract or repel other magnets or magnetic materials without touching them. Whenever a magnet or a magnetic material is within another magnet’s magnetic field, the field exerts a force that either attracts or repels the magnet or magnetic material.

Magnetism and Energy

Imagine that you push two repelling magnets toward each other. You have to use energy to move them together. As you push the repelling magnets together, you apply a force to the system that transfers the energy from your hands into the system. In other words, your pushing force provides an input of kinetic energy into the system.

That input of kinetic energy is stored in the system as potential energy. You can see evidence of this potential energy when you let go of the two repelling magnets. They will move apart from one another. The potential energy stored in the system has been changed back into kinetic energy.

If you change the distance between the interacting magnets, you change how much energy is transferred into the system. For example, the closer you push two repelling magnets together, the more energy you need to use. This means more energy is transferred into and stored within the system. This will cause the magnets to move farther apart when you release them.

Conservation of Energy

In a perfect system, the total amount of energy is always conserved as it changes from one form to another. In other words, however much potential energy the system of interacting magnets has, that same amount of energy will change into kinetic energy as the magnets are released and move away from one another. However, in the real world, some of that energy is transferred out of the system. When energy is transferred, it moves into or out of an object or system. For example, if the magnets move across the ground, friction will transfer some of the energy out of the system.

Speakers work by applying the rules of magnetism. Speakers have two kinds of magnets: an electromagnet and a permanent magnet. Electromagnets are tightly wound coils of wire that produce a magnetic field when electricity passes through the wire. They are useful in various technologies because the magnet can be turned off and on. This is different from permanent magnets, which stay magnetized without electricity.

Electromagnets become magnetized when electricity moves through the wire. Electricity is the flow of electrons through a conductor. Because electromagnets are made with electricity, they can be demagnetized when the electricity is turned off. This is possible because electromagnets form a circuit. A circuit is the circular path that electrons travel in a negative to positive direction.

In this lesson, students use what they know about phenomena of magnetic fields and electromagnets to design speakers that produce sound above a specific sound level intensity. First, students create a visual model of their prototype. They then build their prototype and test it to evaluate its design based on the volume/sound intensity.