The ornamental design for an actuator for loudspeaker, as shown and described.
1.1 is a top perspective view of an actuator for loudspeaker, showing our new design;
1.2 is a bottom perspective view thereof;
1.3 is a top view thereof;
1.4 is a bottom view thereof;
1.5 is a front view thereof;
1.6 is a back view thereof;
1.7 is a right side view thereof; and
1.8 is a left side view thereof.
The broken lines shown in the drawings of the actuator for loudspeaker illustrate portions of the actuator for loudspeaker that form no part of the claimed design.