Van Eck phreaking relies on detecting radio waves produced by equipment like a CRT operating at tens of megahertz, a high-power VRM operating at 500 kHz, or fre

Van Eck phreaking relies on detecting radio waves produced by equipment like a CRT operating at tens of megahertz, a high-power VRM operating at 500 kHz, or frequency shifts in a processor clock operating at a few GHz. These wavelengths can be radiated by antennas of reasonable size. If someone was able to pick up radio waves off a headphone cable, it would probably be from the higher-order harmonics produced by switching power supplies in the amplifiers, not from the sound waves themselves. Also, EMI certification just means that it doesn't generate interference that will damage other equipment and that it's not permanently damaged by external interference. It doesn't mean that it doesn't radiate any energy at all. FCC limits are pretty noisy when you're considering whether or not you can detect emissions with an active antenna.