Abstract: The electro-acoustical transducer comprises a membrane flexible or rigid before assembling, the front portion of which has an aperture with a half-angle .alpha.. In order to obtain sound waves in phase at any listening point, the front portion is the site of vibrations which are responsible for sound emission and are transmitted in the membrane material with a velocity V.sub.m approximating V.sub.0 /cos .alpha., where V.sub.0 is the velocity of sound in air. The membrane is rigidly attached to the transducer chassis and is tensioned under a tensile stress between 5 and 20 KN, in order to the vibrations be bending transverse waves, the vibrational energy of which is totally transferred to air in form of sound waves before reaching the larger end of the membrane. The mechanical-acoustical output is close to unity and the overall energy output lies between 50 and 80%. The displacement of the rear portion of the membrane into airgap of motor is in the macro-deformation field.