How to transmit sound, music, even voice into someone's skull without speakers has been known in the unclassified world for some time now.Indeed. Could it be? I can't say for sure whether or not this sort of experience is actually real, but I can say it's technically possible to broadcast sounds directly into people's immediate auditory environment without having to use loudspeakers. I don't know exactly how the technology works, but it's been out in the public sector for years. Certain types of EM radiation is another possibility. Audio hallucinations are another. Every once in a while I have the stupid doorbell dream. Nobody is there of course, but it wakes me up anyway
Starting in WW II, radar technicians standing in line with medium power radar signals would hear buzzing.
Later experiments by Dr. Allen Frey showed that microwave pulses can be heard as clicks, when pulses are sent individually. Frequency range for this microwave auditory effect is in the low end of the microwave spectrum. Dr. James C. Lin did similar experiments.
Then Dr. Joseph Sharp transmitted one click (microwave pulse) with each of successive audio waveform crests, and showed voice can be transmitted this way. The experimenters believe this is due to sudden heating of flesh by microwave pulses, causing rapid mechanical expansion of the flesh in the vicinity of the auditory pathways.
This Joseph Sharp method can penetrate non-conductive walls, if some way to aim the signal is available, such as police through-the-wall radar imaging.
Fairly recently, it was found that aiming a fairly powerful pulsed laser at someone's skull (ear for best results), using one laser pulse per audio waveform crest, can accomplish the same thing. This experiment is said to generate the sound by rapid expansion of air just outside the ear at each pulse. This would not penetrate walls, but would be heard as if a speaker were on the opposite side of the wall from the intended target.
Finally, a different technique using two ultrasound signals, in which the DIFFERENCE in frequency is modulated by an audible waveform (voice, music, etc.) was demonstrated some years ago. That technology has been available commercially as "HyperSonic Sound" (Woody Norris) or "Audio Spotlight" (Dr. Joseph Pompeo.)
However, this ultrasound method does not penetrate walls. Instead, the audible content is dumped into the environment where the ultrasound beams encounter a solid surface.