Curiosity #1: Understanding Sound
This article is part of the curiosity series in which I will document and share my learnings guided by random curiosity. The purpose is to share knowledge as well as enhance my understanding through teaching.
Sound can be thought of as a wave a “sound wave”, but what does that really mean?
The properties of waves are:
- Amplitude: the height of the wave
- Wavelength: the distance between adjacent wave crests (peaks)
- Frequency: the number of complete waves that pass a point in a second
How can something so simple as a wave produce so many different sounds?
It turns out there are more complex properties of sound, which are given when you look at the pattern within a wave. Sound waves don’t look like the simple wave shown in Figure 1, they actually look more like this:
These complex properties include:
- Pitch: how “high” or “low” a sound is (depends on frequency)
- Duration: how long the sound lasts
- Loudness: how “soft” or “loud” we perceive the sound as
- Timbre: the perception of sound quality
The Science of Dupstep gives examples of these patterns:
How does a sound wave propogate aka “move”?
A sound wave is considered a longitudinal wave, which means that the wave travels in the same direction that the medium is displaced. The medium or material here is air particles. This causes areas of compression (the air particles are closer together) and rarefactions (the air particles are further apart). [http://www.physicsclassroom.com/class/sound/Lesson-1/Sound-as-a-Longitudinal-Wave]
The wave is moving due to air particles bumping into each other. As they do the kinetic energy is transferred from one particle to another, and the compression area moves forward. The fast moving particle (the one with more kinetic energy) will hit the slow moving particle. The slow particle will speed up, while the fast one slows down. When the particles collide, the energy transfers.
How do speakers produce sound?
Speakers produce sound using a diaphragm, actually usually using two.
In the speakers shown above, each speaker has a large diaphragm (for low pitches) and a smaller diaphragm (for high pitches) above that. This is because the amount of air that needs to be pushed to create different frequencies at similar volumes varies. For a high pitch sound, a higher frequency is required, and less air needs to be pushed. For a low pitch sound, a lower frequency is required, and more air needs to be pushed. Internally, the speakers filter the pitches at a certain frequency sending the high ones to the smaller diaphragm and the low ones to the larger diaphragm. But our computers send it over as one stream of data and our ears hear the sounds together as well.
Inside the diaphragm, there is a permanent magnet. The signals from the computer controls a magnetic field which attracts and repeals the iron metal which is attached to the diaphragm cone. The cone is made of a flexible material and is moved due to the magnetic field. This causes air on the outside of the cone to be pushed outwards. The properties of the sound coming out is controlled by the strength, speed and patterns of the magnetic field.
What about sub woofers?
Sub woofers are speakers which usually create much deeper bass sounds which are lower pitch. They are usually sold as a separate speaker with only one diaphragm and are designed to output sounds lower in frequency than the standard speakers. [https://en.wikipedia.org/wiki/Woofer]
How do we capture sound?
Microphones operate similarly to speakers, but almost in reverse.
It uses a diaphragm to sense the compression in the air. “When the diaphragm vibrates, it causes other components in the microphone to vibrate. These vibrations are converted into an electrical current which becomes the audio signal.” [http://www.mediacollege.com/audio/microphones/how-microphones-work.html]
For more info on there internal conversion, check out this quora question and answers: https://www.quora.com/How-do-microphones-work
How does our ears understand it?
ViHart has an amazing video on this; in which she explains what’s going on in our ears to understand sounds:
The Curiosity Series
This article is part of the curiosity series in which I will document and share my learnings guided by random curiosity. The purpose is to share knowledge as well as enhance my understanding through teaching.
Articles will consist more or less of links to information for you to explore as well as some of my notes and summaries. The overarching goal is for us to become more curious individuals, to gain the confidence in our learning capabilities, and to grow our growth mindset.
Call to Action
Now that you’ve learnt the basics of sound, I highly encourage you to pick a further topic and explore! Here are a list of suggestions:
- How about harmonics and chords? What does it mean to have a major key?
- How does a phonograph work? How is sound encoded on the record? How is the sound then produced? How did they record sound onto the record?
- How do we store sound on a computer? How is sound compressed? How is it we can have lossless compression of sound?
- Why are some sounds pleasant to our ears and others not?
