How Does a Speaker work?

📝 Blog Outline:

1. Introduction

2. An explanation of how speakers work

3. What Affects Speaker Sound Quality?

4. What is the difference between speakers and microphones?

1. Introduction

Whether you’re blasting music from your phone, watching movies on your laptop, or playing games with surround sound, speakers are all around us. Have you ever wondered how it works? In this blog, I’ll break down how speakers work, what affects their sound quality, and how they differ from microphones.

2. How do speakers work?

Generally, speakers are devices that convert electrical signals into sound waves. This process is all about electromagnetism and vibration.

When an electrical audio signal flows through the voice coil (a length of copper wire, winding around a permanent magnet), it creates a magnetic field.

Because the voice coil sits in the field of a permanent magnet, this new magnetic field causes the coil (and the attached cone) to move back and forth. This is caused by the repulsions between like polarities and the attractions between unlike polarities.

These movements push and pull the air in front of the cone, creating sound waves that we hear as music or voices. The vibration frequency and amplitude determine the pitch and volume of the sound.

(The two magnets with the same polarity S facing each other, as the diagram above shown, make the magnetic field in the gap becomes more concentrated and symmetrical.)

3. What affects speaker sound quality?

Not all speakers sound the same, and that’s because several factors affect sound quality:

• Speaker sizes:

  Larger speakers, or woofers, can move more air and are better at producing low-frequency sounds like bass. Low-frequency sounds have long wavelengths, so the cone must push a larger volume of air (i.e., a longer air column) to form a complete wave period. This is just like when you push water with a syringe of a larger diameter, which is more effortless than using a syringe of a smaller diameter. In this way, the low-frequency sounds can be heard clearly.

  On the other hand, high-frequency sounds change very quickly and need the speaker cone to move rapidly with precision. Smaller speakers, known as tweeters, are much better suited for this. Because they’re lighter and smaller, they can vibrate faster without distortion.

• Material of the diaphragm:

  Stiff materials like aluminum reduce unwanted bending or distortion, making the sound cleaner. Softer materials might produce a warmer sound but could introduce a bit more resonance or coloration to the tone.

• the quality of the audio signal:

  No matter how advanced a speaker is, it can’t “fix” a low-bitrate audio file. Compressed formats like low-quality MP3s can strip away important audio details, resulting in a thin or grainy sound.

4. What is the difference between speakers and microphones?

Speakers and microphones are closely related—they’re like opposite versions of the same machine.

While a speaker turns electrical signals into sound, a microphone does the reverse: it captures sound waves and turns them into electrical signals. Instead of pushing a diaphragm outward, a microphone’s diaphragm is moved inward by incoming sound waves. This movement affects a magnetic or electrical system inside, generating an electrical signal that matches the sound.

In fact, some microphones and speakers use nearly identical designs—dynamic microphones use a coil and magnet just like a speaker does. Technically, if you wired it right, a speaker could work as a basic microphone and vice versa, though they wouldn’t perform as well as devices designed for their specific task.

In fact, if you use the speaker as a microphone, its sensitivity would be lowered. Because the cone of a loudspeaker is usually large and heavy. If you use a loudspeaker to receive sound, its large and heavy cone is hard to be "driven" by weak sound waves. So even if a signal is generated, the output electrical signal is very small and the sensitivity is low.

References：

Illustrations and diagrams used in this blog are credited to Inspired Pencil and 硬核茶谈