Here I will share the circuit to add bass sound louder, but still pleasing to the ear.
The following circuit uses a single 12VDC power supply, in addition to functioning as a bass sound enhancer, this circuit can also be used as a low pass filter. Unlike the bass/subwoofer filter circuits that are here like: Subwoofer Module Amplifier using 4558 with PCB
This circuit is enough to use asymmetric + 12V voltage, making it easier for you to get the voltage supply. And this circuit using op-amp LM324 as the main sound processor.
Here is a circuit diagram called Giga Bass Pro:
PCB Layout design for Giga Bass Pro: