Whats the ringing noise on the phone when your calling someone?

Question

whats the ringing noise what makes it?

Answer 1

In the old days there could be considerable variation in the ring tones between one central office and another, due to the different types of ringing machine.  

The machine was basically just an electric motor rotating a shaft on which were mounted several disks with magnetic castellations around the edges.  As these disks spun round, they induced currents in coils placed around them, the frequency being dependent upon the spacing of the castellations around the disk.  

A 20Hz signal was used to generate the actual voltage used to ring the bell on the phone being called.  Other, much higher frequencies, provided the signals for dial tone, busy tone, and ringback tone, the latter generally being a tone of around 400 to 500Hz modulated by the 20Hz ringing voltage.  

Some very small offices used vibrator relays to generate tones, operating very much like one of the old-style electric door buzzers.

In modern telephone systems, the tones are all generated electronically with oscillators, pretty much the same way as the notes are generated in an electronic organ or synthesizer.

In the U.S. system, the modern electronic ring tone consists of a 440Hz tone and 480Hz tone mixed together.  Whenever you mix two different frequencies, the result is the sum and the difference, as well as the two original tones.   It is the 40Hz difference frequency between these two tones which you hear as the low-sounding element of the modern ring tone.

Answer 2

The thing that makes the noise is called a "ring generator". It sends out an AC voltage at around 20Hz that operates the "ringers" in the telephone sets. In the old days, the ring generator was a mechanical device that looked something like a large electric motor. These days I'm sure that the sound is synthesized electronically.

For more information, see http://www.telephonetribute.com/signal_a...