Injection Molded Earbud Housings

The driver pushes air into a small sealed volume behind it and out through the nozzle toward the ear. Vents and ports tune the bass and relieve pressure. If the seam between the two shell halves leaks, the tuning changes, and two earbuds from the same line sound different. The seam is therefore designed as a seal from the start.

Ultrasonic welding is the usual way to close it. A small raised ridge, called an energy director, runs along the joint on one half. Vibration melts it into the other half and forms a continuous bond. That only works if the two halves match along the whole seam, so each half is checked against its mate, not just against its own drawing.

Acoustic ports are small holes, often covered by a fine mesh set into a seat. Flash across a port, or weld flash falling inside, blocks or rattles. Ports are placed away from where flow fronts meet, and the mesh seat is kept clean and flat. Charging contacts are usually insert molded or pressed in and sealed, so sweat does not get in around them.

Cosmetics are demanding for such a small part. A glossy shell shows every flow line, gate vestige, and sink. Gates go on inner faces or under the ear tip, often as sub gates that shear off on ejection. Matte textures hide more but wear shiny where skin rubs. The charging case adds a hinge and magnets, and follows the same cosmetic rules. Many small shells are often run in one tool, so the halves are tracked by tool position when matching them for welding.