After you have the diagram, construct the product on the assembly station.
The Loudspeaker can be obtained for free by giving 5 Data Discs to Petra during Mission: Panbat Infestation. The Boombox and the Loudspeaker can be taken simultaneously by providing 8 Data Disks altogether. However, if only the Loudspeaker is taken, the other diagram is given at the end of the year through the mail.
Loudspeaker (Diagram) can be used to learn how to make Loudspeakers.
9 Copper Plate
2 Simple Circuits
2 Copper Coil
4 Hardwood Plank