hap-jackson
02-20-2008, 04:31 PM
Why do my TV and PC speakers make a buzzing noise when ever my cell phone is about to ring?
scienceking
02-20-2008, 05:38 PM
You are hearing your cellphone's radio. It generates noise which then gets picked up by wires/traces in those devices. This noise is very small in magnitude and power, which is why its harmless and unpowered speakers and what not will not pick it up. But it is pretty large compared to pre-amp signals in many devices , so basically anything that has an amplifier will end up amplifying it to a level you can definitely hear. So basically, the wires on the input side of amplifiers pick up the signal FROM your cell phone, and the amplifiers amplify it up to something you can hear. Its of note that you don't hear the actual signal, but an aliased version.
Since most transistor circuits are amplifiers too, you can get some weird effects from this. For example, my shaver responds to my cell phone, because the electronics that drive the motor apparently have an insufficient noise margin to stop my cellphone signal rather than the logic signal from triggering the motor drivers.