Install an led light on the speaker of the small speaker, which flashes with the music.

Absolutely. First, lead out the two wires on the subwoofer horn, and then pass through the full-bridge rectifier circuit. The rectified anode is connected to the anode of the LED light bar through a resistor of 3W10Ω, and the rectified cathode is directly connected to the cathode of the light bar.

If you find it necessary to turn up the volume, it means that the current limiting resistance on the light bar (the small black rectangle on the light bar in your picture) is too large and needs to be reduced. Try to reduce it all to half, if not, reduce it to one third. I believe it will succeed.

After the transformation, he will consume certain skills, so the load of the power amplifier will increase. Pay attention to the heating of the power amplifier, and turn down the volume if it is serious.

Bridge rectifiers don't search online, it's simple.

If it helps you, take the answer.