posted on Jul, 11 2004 @ 09:57 PM
I live next to the Gulf Freeway and I had a system back in the late 70's that I made, AM, FM, Turntable, remember those, anyway, the speakers used to
produce loud sounds from the people, mostly truck drivers driving down the freeway while talking on their CB radios with the system off. As they
would get within 200 or 300 yards while driving down the road the modulation (voice) due to the induced signal through my speakers would allow me to
hear their conversations at about 10 or 14 decibels and it would increase at a rapid rate to about 30 or 40 or so decibels when the truck was closest
to my house and then it would disipate at a constant rate til the truck was about 3 or 4 hundred yards down the road.
It has to do with the coil that surounds the magnet at the center of the speaker. It picks up the radio frenquency modulation (FM) or amplitude
modulation (AM) which rides on top of or is a part of the carrier wave which is nothing more than electricty flowing through the air. The electric
current is induced through the speaker coil changing the position of the coil to the magnet creating vibration and sound through the speaker cone via
inductive current. In other words it is induced through the air instead of being induced through a DC carrier and AC modulation as would normally
happen when listening to the radio.