Abstract: A sonic transmitter assembly for use in logging-while-drilling includes stacks of piezoelectric crystals that extend outwardly from a nodal plate member, and a generally tubular assembly that contains such stacks and has end portions that are sealingly mounted in diametrically opposed holes in a pipe member that forms a pan of the drill string. Spring mass isolator systems are employed to inhibit transmission of acoustic waves to the pipe member. Balanced mounting forces and the bilateral symmetry of the construction also inhibit transmission of acoustic waves to the pipe member, particularly waves which are asymmetric with respect to the longitudinal axis of the pipe member.