The wall comprises a closed acoustic box-structure which is defined by a slightly ribbed sheet and a flat sheet. The box-structure has lateral ribs which extend beyond the sheet. A panel of high-density mineral wool which is of small thickness is enclosed inside the box-structure. A heat insulator covers the box-structure and the ribs of the box-structure and is protected by an outer trough which has ribs or corrugations perpendicular to the ribs of the box-structure.