A digital sound processing design system for a vehicle audio system includes a computer and a design tool that is run by the computer. A representative embodiment of a terminal housing body for receiving a wire pair, the terminal housing body having a front end and a rear end, includes a base wall having a top portion. Multiple sectors are formed on the recording disk, and the head assembly includes a head for readingwriting data fromto the recording disk. A charging apparatus into which the battery is to be installed includes an accommodating section for the battery which in turn includes projection accommodating portions configured to individually accommodate the projecting portions.