Are sound-powered circuits polarity sensitive?

• A. Yes
• B. No
• C. Only with DC
• D. Only with AC

Answer: (B)

In sound-powered circuits there’s no external power and no fixed polarity. The signal comes from the operator’s voice, which modulates the current on the line as an alternating waveform. The microphone/earphone combination in these devices is non-polarized, so it responds to the magnitude of the audio signal, not the direction of current flow. Reversing the leads simply flips the waveform’s polarity, but the audible result is the same because the transducers convert the same magnitude variations into sound. That’s why polarity doesn’t matter in these circuits.