The Echofone has two outputs - one to the high frequency transducers, which are like little speakers, except that instead of a paper cone which vibrates, these transducers have a metal plate which vibrates. The second output goes to normal headphones which you place over your ears.
The high frequency transducers, you place on your temples or other places on the head, and they are supposed to transmit the high frequencies to the brain via bone and skin conduction.
I am able to hear the sound from the transducers using my ears (normal hearing), which leads me to believe that the transducers send a combination of normal audio signals (which I hear using my ears), and higher frequencies, which I "hear" through bone conduction.
The difference between using just the headphones, and using the headphones and the Echofone transducers, is that sounds appear to more 3-D in nature, and definitely more clear, because of the higher frequencies being transmitted by the transducers.
I am trying to discern how much of an effect using the Echofone has when using paraliminals or other accelerated learning techniques, because that is what the Echofone brochure says it can help with.