An investigation on the acoustical characteristics of an electromagnetic hemianechoic room is here proposed. The research has been carried out within an agreement between the Perugia University Acoustic Laboratory and Angelantoni Industrie S.p.a. Angelantoni Industrie hemianechoic room has been investigated. The room has been created for electromagnetic compatibility tests. It is fully insulated from the outside environment and it guarantees more than 10 KOhms of insulating power. A hybrid solution has been chosen for the anechoic lining of walls and ceiling; the ‘quiet zone’ is covered by 24” cones coupled to ferrite tiles whereas the remaining parts are covered with 36” cones. No fixed anechoic insulation is on the floor (hemianechoic type). An acoustic measurement campaign has been carried out in order to verify if the investigated room is characterized also by high acoustic hemianechoic performances. Measurements have been led according to ISO 3745. Measurement results have shown that the investigated room, differently from the acoustic typical hemianechoic rooms, accords to ISO 3745 only for 315-20000 Hz frequency range and for a 2.5 m radius hemispheric surface.