Audio Electronics
How electronics turns sound into electricity, and back into sound again.
The question
How does your voice get from your mouth, into a phone, and out of someone else’s speaker?
What you’ll discover: how microphones and speakers convert between sound and electricity, why we need amplifiers, and how to protect your hearing.
In simple terms
BeginnerSound is a wave in the air
Sound is air being pushed and pulled in tiny, fast waves. The faster the waves (higher frequency), the higher the pitch. Young people can usually hear from about 20 Hz (a deep rumble) to about 20,000 Hz (a very high whine); the top end drops as we get older.
A transducer changes one kind of energy into another:
- A microphone changes sound into a tiny, wiggling voltage that copies the sound wave.
- A speaker does the reverse: a wiggling current makes a cone move, pushing the air to make sound.
How a speaker works
Inside a speaker, a coil of wire (the voice coil) is attached to a paper or plastic cone and sits around a strong magnet. When current flows through the coil, it becomes an electromagnet and is pushed or pulled by the permanent magnet, the same force that spins a motor (Lesson 13). As the current changes direction many times per second, the cone moves back and forth and makes sound.
Many microphones use the same idea in reverse: sound moves a thin diaphragm, and the motion makes a small voltage.
Go deeper
IntermediateAmplifiers
A microphone’s signal is tiny, often just thousandths of a volt. An amplifier uses transistors (Lesson 10) to make a bigger copy of a small signal, powered by a battery or power supply. The gain tells you how many times bigger: a gain of 100 turns 0.01 V into 1 V.
Push an amplifier past what its power supply allows and the tops of the waves get flattened, called clipping, which sounds harsh and distorted.
Speakers are rated in ohms (often 4 or 8 Ω). That low resistance is why a microcontroller pin (Lesson 23) can’t drive a speaker directly: it needs a transistor or an amplifier chip in between.
AdvancedDecibels and hearing safety
Loudness is measured in decibels (dB). The scale is logarithmic: every 10 dB increase means about ten times the sound power, and our ears hear it as roughly twice as loud. Normal conversation is about 60 dB; a lawn mower or a loud concert can be 90 to over 100 dB.
Loud sound can damage the tiny hair cells in your inner ear, and that damage is permanent. The louder the sound, the less time it takes. With earbuds, a good habit is to keep the volume at a level where you can still hear someone talking to you nearby, and take breaks. When testing audio projects, start with the volume low and keep speakers away from your ears.
Quick check
What is a transducer?
A device that changes one form of energy into another, like sound into electricity.
Why can’t a microcontroller pin drive a speaker directly?
A speaker has a low resistance (4 to 8 Ω) and needs more current than a pin can safely supply.
What does an amplifier’s gain tell you?
How many times bigger the output signal is than the input.
Words to know
- Transducer
- A device that converts one form of energy to another.
- Amplifier
- A circuit that makes a bigger copy of a signal.
- Gain
- How many times an amplifier increases a signal.
- Decibel (dB)
- A unit for comparing sound levels.
Electronics School is part of the Discovery Zone. Every activity here runs on small batteries or a USB cable: never wall outlets. The one plug-in tool is the optional soldering iron, set up by an adult.