We report on sound-echo experiments at 70 and 150 GHz using a 3-mm-thick type IIa diamond with a (100) cut. Longitudinal sound was piezoelectrically excited and detected by means of a sputtered ZnO film. The method of linear frequency modulation of a continuous wave was applied. The temperature dependence of sound attenuation could be measured at 70 GHz up to a temperature of 200 K where an attenuation of about 1 dB/mm was observed. ©1997 American Institute of Physics.