SolidDrive is a sound transducer that transmits acoustical energy through almost any solid surface. By converting audio signals into vibrations, walls (including drywall), windows, tables are transformed into speakers. Each transducer can be equipped with an optional passive equalizer module that will adjust the EQ to match the surface material that the SolidDrive transducer is mounted to. The main selling point of the SolidDrive is that you can completey hide your audio source from view. By attaching a SolidDrive transducer to a large surface area, the listener is immersed in an omni-directional sound field. A pair of SolidDrive transducers cost about $500.