Inside a Speaker: How They Convert Electricity into Sound and Are Built

The speaker is designed to translate an electrical signal into an audible sound, which contains an electromagnet (coil), a permanent magnet and a cone. In this post, you’ll know the secret networking among the 3 key components in a speaker and the demonstration of the manufacturing process.

1. What does a speaker consist of?

The most common type of speaker uses a lightweight cone. It connects to a rigid basket via a flexible suspension (spider), that constrains a voice coil to move axially through a cylindrical magnetic gap.

2. How do speakers work?

When a fluctuating electric current flows through the coil (orange), it becomes a temporary electromagnet, attracted and repelled by the permanent magnet (blue/red). As the coil moves, it moves the cone (gray) back and forth, pumping sound waves into the air (light blue).

3. How are speakers made?

3.1 Frame and magnet assembly

• Construction of the magnet: The  magnet is constructed by mixing Fe_xO_y with Sr, and then milling into a very fine powder. The powder is mixed with a ceramic binder, and then closed in a metal die to bond the mixture together.
• Construction of the frame: The frame is constructed from an Al or steel sheet. Cutting machine was used to cut holes in the sheet to allow free air movement from the cone. The sheet is then  forced into a die of the desired shape.
• Assembly: The frame and permanent magnet are bolted together as an assembly.

3.2 Cone and voice coil assembly

• Construction of the cone: The cone, surround, and spider are individually formed out of composite paper and then glued together as an assembly.
• Construction of the voice coil: The voice coil is built by winding many turns of very fine insulated Cu wire on a plastic bobbin.
• Assembly: The bobbin and voice coil assembly is glued to the dust cap of the cone assembly.

3.3 Cone and frame assembly

The cone assembly is then attached to the frame assembly.  Firstly, the spider is manually glued to the base of the frame, and then the surround is glued to the top of the frame.

3.4 Quality control (QC)

The permanent magnet is checked for chips or cracks. The cones are inspected for flaws or holes in the material, and proper gluing of the cone assembly. The entire assembly is inspected for overall quality and adherence to specifications.

The final speaker assembly is connected to an audio generator that tests the frequency response and power capabilities of the speaker to ensure that it produces sound within the required specifications.

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