An ultrasonic transducer device comprising a casing which encloses a piezoelectric device, wherein the piezoelectric device comprises an internal ventilation path (13, 11, 14) for the passage of cooling air from the outside of the piezoelectric device to the outside of the casing, wherein the device comprises a connection plate comprising a body which extends inside the casing and which has a mass calculated in accordance with the mass-spring-damper model, a hub centrally extending from the connection plate and protruding outside the casing, the hub being configured for the connection with an operating member, for example a sonotrode, wherein the connection plate comprises a seat comprising at least one threaded portion and wherein the piezoelectric device comprises: - a piezoelectric element sandwiched between the body of the plate and a countermass element, wherein the piezoelectric element and the countermass element comprise respective central holes aligned with the seat of the connection plate, - a fastening element inserted in the aligned holes of the countermass element and of the piezoelectric element and fastened into the seat of the connection plate by screwing, and - a plate made of metallic material, placed between the piezoelectric element and the countermass element so as to form a contact element connectible with an electric power source, the fastening element comprising a head, a central portion and an end portion, wherein: - the head has a diameter greater than the one of the central portion; - the end portion is threaded and is sized so as to couple with the seat of the connection plate by screwing; - the central portion has a frustoconical shape, tapered towards the end portion, and has a diameter always smaller with respect to the internal diameter of the holes which pass through the countermass element, the piezoelectric element and a first part of the body of the connection plate, so as to form a toroidal spacing between the fastening element and the internal walls of the countermass and piezoelectric elements, wherein said toroidal spacing is flared passing from the countermass element to the body of the connection plate and comprises a section of smaller section at the countermass element and a section of greater section at the body. - a piezoelectric element sandwiched between the body of the plate and a countermass element, wherein the piezoelectric element and the countermass element comprise respective central holes aligned with the seat of the connection plate, - a fastening element inserted in the aligned holes of the countermass element and of the piezoelectric element and fastened into the seat of the connection plate by screwing, and - a plate made of metallic material, placed between the piezoelectric element and the countermass element so as to form a contact element connectible with an electric power source, the fastening element comprising a head, a central portion and an end portion, wherein: - the head has a diameter greater than the one of the central portion; - the end portion is threaded and is sized so as to couple with the seat of the connection plate by screwing; - the central portion has a frustoconical shape, tapered towards the end portion, and has a diameter always smaller with respect to the internal diameter of the holes which pass through the countermass element, the piezoelectric element and a first part of the body of the connection plate, so as to form a toroidal spacing between the fastening element and the internal walls of the countermass and piezoelectric elements, wherein said toroidal spacing is flared passing from the countermass element to the body of the connection plate and comprises a section of smaller section at the countermass element and a section of greater section at the body.