With the core of GMM (abbreviation of� â��rare earth giant magnetostrictive materialâ��) and GMM audio transducer, vibration resonance speaker is the result of integration of many advanced technologiesï¼� give you wonderful tone better than any other mini speaker, let every mini speaker look feebleness. Works perfectly on any solid surface: Glass, wood, plastic, stone, ***** wondered, it can change every table into a speaker, the sound effect is different depend on different material and structure.