Hey all,

Since we’re not going to meet in person because of COVID-19, I’m leaving a couple of resources on our class page to hopefully show you how to get started learning about audio and sound and how that plays into making technological/electronic devices like earphones and speakers that allow us to hear music.

Part 1: Introduction

This is the BOSEBuild Speaker Cube, A Build-it-yourself Bluetooth Speaker meant to show you how two basic components that make up a speaker, the coil of wire and a magnet, come together to make sound!

Since we can’t show it to you in person, here’s a video that shows how it works:

Part 2: How does sound happen?

Sound happens in pressure waves. When particles in the air are compressed and de-compressed (or rarefied), it produces a “wave”.

Every time we move around, we are compressing air particles around us. However, not all air pressure changes will produce “sound”. We hear sound when the motion of the wave being created becomes fast enough. At that point, our ears start to perceive the changes in air pressure as sound. That’s why when you pluck a guitar string, it makes a note: The string is vibrating fast enough so that the wave being produced is perceived as sound. Different strings vibrate at different speeds, so we hear different notes, or pitches.

Fun fact: Human’s hearing range goes from about 20Hz to 20,000Hz (Hz is a pitch measurement), but other animals like cats and dogs can hear sounds well above 40,000Hz.

Here’s a “hearing test” video that goes through the entire range. Try to see at what pitch you start hearing sound and at what pitch you can’t hear it anymore. (Warning: Please adjust your volume slowly, you might not hear anything in the beginning): 

Here’s another video that goes in depth on how sound is made, from a more scientific/physics perspective:

*look for the part where the narrator explains why an ambulance’s siren sounds a lot higher in pitch as it moves closer to you but starts getting lower as it moves away!

Part 3: How does a speaker create sound waves?

You now know how all you need a speaker to do to make sound is to be able to move air particles at the right frequency to produce a wave, so we are able to hear it as pitch. But how does that happen?

A speaker is made up of three components: the cone(1), the coil or electromagnet (2), and the permanent magnet (3).

Inside a speaker, an electromagnet (coil) is placed in front of a permanent magnet. The magnet is fixed firmly into position while the coil can move.

When you play music, you send pulses of electricity through the coil, which changes the direction of its magnetic field. This means that it will be attracted and repelled by the permanent magnet really quickly. This is what converts the electronic signal (pulses) to actual movement.

If you’ve ever played with magnets you know that “like charges repel each other and different charges attract. ” The movement of the electromagnet being repelled and attracted to the magnet back and forth causes the cone to vibrate, producing a sound wave.

The cone is made of flexible material such as plastic or paper so that it can amplify the vibrations really easily. Its in a ‘cone’ shape so the sound can travel outwardly towards your ears!

Here’s a video explaining how this all works. Here they use a battery to send the pulse:

More resources:

http://www.physics.org/article-questions.asp?id=54