Serial number 2767 I am selling this because I am not currently active in a band. I haven't taken it out of the house, so the condition is quite good, and there are no issues with the sound or crackling. The speaker sounds better from the start than a new one. Please note that this is not the current Double Four plus model. The following is the manufacturer's description: This is a professional-grade bass amplifier that, while even smaller than the standard Bass CUB, delivers authentic sound that is just as good. The 4-inch speakers are driven independently by the amplifier, resulting in outstanding response. It produces a clear and punchy tone. PWM digital power amplifier, clear sound quality with digital control From the preamp to the power amp section, it is fully digitally controlled, and the PWM circuit (pulse width modulation circuit) features speed and noise-free sound. PWM stands for Pulse Width Modulation. RALFR passive radiator, the secret to bass beyond its size The secret to producing authentic bass is the RALFR passive radiator on the back. This is an innovative system that reinforces low frequencies from 30 to 150 Hz. A passive radiator is a RALFR Rectangular Auxiliary Low Frequency Radiator.