Abstract: A speaker is installed on a door panel of an automobile by utilizing a supporting unit including a base and a substantially disc-shaped spacer. The base is attached to the door panel and has a bottom surface inclined with respect to the door panel. The speaker is secured to the inclined bottom surface of the base by an attachment screw, between which the spacer is interposed. The spacer has an inclined surface adapted to be in contact with the inclined bottom surface of the base. The spacer is provided with a half-round groove through which a screw extends to secure the spacer to the base at a desired position relative to the latter within an range of 180.degree. rotation. The inclination of the base is amplified or counterbalanced by the inclination of the spacer in dependence with relative position therebetween to vary the orientation of the speaker supported on the opposite surface of the spacer.