Two full-range (bass/treble) car speakers go into two 6.5-inch pre-cut speaker boxes: the positive and negative leads pass through the wiring hole, and the speakers are screwed in. The amp is an XY-T30L module with Bluetooth and bass/treble control; plug in the left and right channels, the speaker terminals are screwless, and it runs on 12 or 24V. To keep things simple for the older folks, he builds a dedicated power supply: 15 × 18650 cells with fish paper on the positive ends in a dedicated holder, 3S5P for 12V, fish paper around the outside against knocks, then spot-welded. A balancing BMS is a must; the multimeter reads 10.8V at input/output (not fully charged, normal), 3.6V for one group and 7.2V for two. The common-port input/output leads are connected and protected with fish paper + fibre tape. The box is drilled for a switch, battery gauge, charge input and power output; charging uses a 5–30V-input constant-voltage/constant-current buck-boost module set to about 12.6/12.7V, insulated with heat-shrink. Battery output and charge input both go to the switch input; all negative leads are twisted together, tinned and heat-shrunk. On power-up the gauge shows 2 bars; the lid goes on with screws, the phone connects over Bluetooth and plays, and the creator claims ¥1000-class sound quality. Commenters think the box size doesn’t match and a digital amp is just loud.