[TenTec] Inexpensive, readily available, light-weight, communications design headphones... mono but easy to make stereo

[Stuart Rohre]

The leads inside the coiled cord are not often tightly twisted upon each 
other, and that is what is needed to effectively cancel pick up.  The coiled 
cord may have one conductor that makes a very gentle curve but basically 
remains near the outer jacket the whole length of the coil cord.  It thus 
acts as a wire antenna to RF.  The thickness of the typical coil cord 
precludes much RF choke action although there might be some inductance to 
RF.  The insulation spacing the turns creates a lot of interwinding 
capacitance.

Stuart
K5KVH