Self-amplified Car Subwoofer with box Pervoi CTC-8031 by PerVoi. This speaker has a nominal power (RMS) of Watt and a diameter of inches. The box helps in enhancing the bass. Self-amplified Subwoofers like this one have a built-in amplifier, so they do not require an external amplifier, unlike passive speakers, to operate. However, it should be noted that due to the heat generated by the amplifier, the air inside the speaker chamber heats up, which can affect the sound quality.