Sound eh?

[etoven]

The oldest used those speakers and microphones, but after that modems don't have a single instance from start to finish in which the data has to be transferred via sound waves. It can all be converted into sound (as in that dial-up sound and what you hear if you pick up the hook), but without a speaker it's all electrical impulses.

But modems don't use electrical impulses. It has to use different tones and pulses in order to meet FCC requirements for telephone communications. If it were simply sending electrical impulses threw the wires, half of the signals would be filtered out by the switching stations, the bytes are converted into telephone standard complaint tones in order to pass threw the switching stations. That's why you here the tones when you pick up the headset.

BTW: Basic Circuit Design......
Electrical Impulses don't produce sound when passed threw a speaker. They have to be modulated into pulses first. Unless of course your using a Pazo buzzer/speaker in which case the Pazo crystal modulates the current.