A lightweight accelerometer in a casing or housing, having a very small base member to mechanically contact a surface, vibrations of which are to be determined; a piezoelectric element connected to the base, a seismic mass connected to the piezoelectric element, at least one thin circular diaphragm peripherically fixed to the housing, and with the base, the piezoelectric element, and the seismic mass fixed on, and axially symmetric to, the center of diaphragm and a soft pad member on the housing providing support on and dynamically isolating the housing from the vibrating surface. Several embodiments are disclosed and in each embodiment vibrations are directly transmitted from the vibrating body or surface to the piezoelectric element through the base, a very small half of a steel sphere.