I visited many sites and did lots of Google search but I didn't get my answer.
In this link I read the article about how Sgnl works. and here's some text:
"Sgnl will generate vibration through its Body Conduction Unit (BCU) which transmits the vibration through your hand to your fingertip. When you place your fingertip to your ear, the vibration echoes to create amplified sound within the closed space of your ear."
I am interested to know the physics concept behind how the BCU makes vibrations and the vibrations is converted to sound. As described in the text this device allow us to hear without wire and any other device on ear My question is how? Is it just sending sounds through solids or It has a complexity Why isn't energy lost by materials in the body? Why is difference a lot between input and output in range of 2000 Hz to 20000 Hz?