Engineering a Speaker: vibration, sound waves, electricity, and electromagnetism build challenge

By: Meghan Thoreau, OSU Extension Educator

Dr. Betty Lise Anderson, Professor of Electrical and Computer Engineering at The Ohio State University is pictured engaging Ashville Elementary students on principles of sound, magnetism, electricity, and constructing a speaker.

This year’s STEM Club started by welcoming guest educators Dr. Betty Lise Anderson and Lecturer, Clayton Greenbaum, both from OSU’s Department of Electrical and Computer Engineering. Each led students to explore more concepts on vibration, sound waves, electromagnetism, magnet fields, current (I), and how to build an electromagnet to use in constructing a working speaker project to take home. It’s our hope that the students plug in their speakers and share what they learned in our club meeting with their families.

Dr. Anderson runs a popular ECE outreach program that helps K-12 students, and their teachers explore electrical and computer engineering concepts with a variety of hands-on electrical projects. This program is specifically designed to encourage students toward STEM fields and to specifically increase the number of women and minorities in engineering. In 2015, the program won Ohio State’s top university-wide Outreach Award.

Ashville elementary students building to construct their speaker.

Along with the team of Educators, several OSU college students’ volunteers, and Teays Valley High School volunteers came to mentor the elementary students and provide additional opportunities for students to engage and ask questions.

OSU college students teaching magnetism concepts with Walnut elementary students.

How does your ear process sound waves?

Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.

The bones in the middle ear amplify the sound vibrations and send them to the cochlea, which is filled with fluid. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells, sensory cells, sitting on top of the basilar membrane—ride the wave. Hair cells near the wide end of the cochlea detect higher-pitched sounds, such as an infant crying. Those closer to the center detect lower-pitched sounds, such as a large dog barking.

As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cells, creating an electrical signal.

The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we recognize and understand. (1)

What is an electromagnet?

An electromagnet is a coil of wire wrapped around a ferromagnetic material that becomes magnetized when electric current flows through it. Electromagnets are used in common electric devices. Here is a close-up of an electromagnet the students coiled up and attached to the base of their paper diaphragm.

Slow-motion video of speaker (note this one is driven by a source a little more substantial than a cell phone!) Credit: Clayton Greenbaum.

Why does a speaker need an electromagnet?

Every speaker has an electrical current. When the current is changing, it produces a magnetic field. To make the cone (or panel) of the speaker move, magnets are used to create an opposing magnetic field which creates vibrations. These vibrations are the sound we hear.

Lecturer, Clayton Greenbaum leads a club meeting highlighting the speed at which technology advances exponentially and the importance of students understanding the immediate need for problem-solving minds to enter the workforce and solve problems created by human technologies. 

1 U.S. Department of Health and Human Services. (n.d.). How do we hear? National Institute of Deafness and Other Communication Disorders.,malleus%2C%20incus%2C%20and%20stapes.


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