What are the physics of a telephone?

Speaker's Vocal Chords ===

  • The person speaking into the phone passes air by their vocal chords making a basic tone, the mouth then shapes the tones into words. Audible Sound Waves are produced that propogate toward the phones microphone.

Microphone / Transducer

  • The microphone or transducer will respond to the sound waves and convert mechanical energy into electical energy. This is typically through the reverse mechanices of a speaker. In this case, the cone shaped "floating" mechanical piece reacts to the sound waves of the person speaking into the phone. This creates an oscillating motion that moves a electrical coil around a magnetic field. This produces oscillating electrical voltage/current in proportion to the speed that the microphone oscillates. At the output of the microphone is a sinusoidal electrical wave form.

Analog to Digital Converter (A-D Converter)

  • The analog electrical signal has to be digitized so that we can take advantage of computer processing in the transmission. An Analog to Digital Converter is used.

Compression Algorithms

  • Sending the entire raw signal takes too long. The signal is passed through a modified Fast Fourier Transform FFT routine to come up with the basic waveform coefficients.



  • The person being called picks up their receiver when their phone rings and the process reverses itself.


Digital to Analog Converter (D-A Converter)

Telephone Speaker