(passive) A piece of circuitry is termed active if it needs a power supply for it to function. (Active DI box, Active crossover etc.) Circuitry that needs no additional power supply is termed passive (eg resistors & capacitors in a crossover). Passive circuits use the electrical sound signal itself to operate the components. OR A piece of circuitry is termed active if it amplifies a signal supplied to it. A passive circuit does not increase the level of a signal.