An energy saving PWM sound device forms a frequency-dependent impedance device implemented on the PWM output of the voice-ICs in series to lower the power consumption and to enhance sound quality of the voice-IC products. The device includes a hollow core body and an elongated conductive element. The core body has a top rim, a bottom rim, and two side rims to define a through channel therewithin. The conductive element winds around the top rim of the core body, wherein two ends of the conductive element are adapted for connecting with the PWM output, such that when the conductive element is electrically conducted, the core body acts as an inductor at lower frequency and a frequency-dependent resistor in series with the inductor at higher frequency for blocking most of PWM carrier frequency so as to reduce the power consumption of the voice-ICs product.