Answer to Question #134352 in Physics for rose auburn

Question

Normal telephones do not transmit pure tones with frequencies below about 300 Hz. But a person whose speaking voice has a frequency of 100 Hz can be heard and understood over the phone. Why is that?

Answer 1

In this question, frequencies of voice (mechanical oscillation of air molecules) are mixed with electromagnetic frequency (how many times an electric current changes within one second).

Men speak so that the molecules of air oscillate 85-155 times per second (one time per second is Hertz, or Hz) in the direction of sound. Women speak with voice frequency of 165-255 Hz.

The oscillating molecules of sound push the membrane of microphone in the telephone, which converts (modulates) mechanical oscillations into electrical impulses by means of various digital circuits.

300 Hz in the question is the frequency of electrical impulses that provides stable transmission of electrical signals over the line. Then, on the other end of the line, in the telephone speaker the electrical impulses create magnetic field that make the membrane mechanically oscillate and create sound that a human ear can hear.