Ep. 41 | Home speakers built from car speakers — surprisingly good? Turning car audio into a home stereo that sounds this good

Two 6.5-inch full-range car speakers + a Bluetooth amp board + a 15 × 18650 3S5P 12V power box: a home stereo for under ¥100

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.

Outcome

Steps9 steps · click a frame to jump

1. 
   1. Goal: a home stereo for under ¥100

   Two car speakers turned into a home stereo, under ¥100, done in a few steps.

   00:00 – 00:14
2. 
   2. Box the speakers: run the wires, screw them in

   Full-range car speakers + 6.5-inch pre-cut boxes; the positive and negative leads go through the wiring hole at the back and come back out; screws go around the speaker cut-out; pull the leads out, connect the speaker, fix it in place, same for both.

   00:14 – 00:54
3. 
   3. Fit the XY-T30L Bluetooth amp

   Amp module with Bluetooth and bass/treble control; plug in the left and right audio leads, the speaker terminals need no screws; feed it a matching 12V or 24V supply and it’s done.

   00:54 – 01:09
4. 
   4. 15 × 18650 into a 3S5P 12V pack

   A dedicated power supply for the older folks; fish paper on the positive ends, into the dedicated holder with the cap on; 3S5P for 12V; fish paper around the outside against knocks, then spot-weld.

   01:09 – 01:48
5. 
   5. Why 12V

   The car speakers and the amp module both run on 12V (or 24V), so the pack matches.

   01:48 – 02:02
6. 
   6. Fit the balancing BMS, measure the voltages

   After spot welding a balancing BMS is a must; the multimeter reads 10.8V at input/output (pack not full, normal), the same at the main + and −, 3.6V for one group and 7.2V for two; connect the common-port input/output leads, cover with fish paper, fibre tape around the outside, and wrap the exposed + and − in fish paper too.

   02:02 – 02:44
7. 
   7. Drill the box, fit the 5–30V buck-boost charging module

   A round hole for the switch, a square one for the gauge, a charge input and a power output on top; the CV/CC buck-boost module goes on the charge input — feed it 5–30V from an adjustable supply, set its output to about 12.6/12.7V, wire + and −, screw it to the box floor, heat-shrink over the output leads.

   02:44 – 03:21
8. 
   8. Wire the switch, gather the negatives, power-on check

   The battery output and charge input leads go to the switch input, the switch output to the gauge positive; all negative leads twisted together, tinned and heat-shrunk; power on, the gauge shows 2 bars, the wiring is fine, lid on and screwed tight.

   03:21 – 03:48
9. 
   9. Bluetooth playback and verdict

   The 12V power box drives the home-built speakers; the phone connects over Bluetooth and plays; the creator says it sounds like a ¥1000 system, fine for karaoke at home or the older folks’ dancing.

   03:48 – 04:21

Bill of materials

Measured on camera

Creator’s tips

• Match the pack voltage to what the speakers / amp need (car audio 12V, amp 12/24V) 01:48
• With the BMS connected, check with a multimeter: 10.8V when not full is normal, then measure one group / two groups to confirm balance 02:09
• Feed the buck-boost charging module from an adjustable supply first and set its output to 12.6/12.7V before connecting the battery 03:04

Li-ion safety

• A balancing BMS is essential when building a Li-ion pack 02:00
• Fish paper on the positive ends, fish paper around the outside so knocks don’t damage the cells, and wrap the exposed + and − too 01:21
• Tin the joints, then insulate with heat-shrink 03:18

Quotes

Cost & time