The ornamental design for a loudspeaker, as shown and described.
FIG. 1 is a front perspective view of a loudspeaker according to the new design;
FIG. 2 is a front view of the loudspeaker;
FIG. 3 is a back view of the loudspeaker;
FIG. 4 is a top view of the loudspeaker;
FIG. 5 is a bottom view of the loudspeaker;
FIG. 6 is a right side view of the loudspeaker;
FIG. 7 is a left side view of the loudspeaker;
FIG. 8 is a back perspective view of the loudspeaker, shown in an environment of use; and,
FIG. 9 is a cross-sectional view of the loudspeaker taken in the direction of line 9-9 in FIG. 2.
The broken lines in FIG. 8 showing framing and additional loudspeakers depict environment and form no part of the claimed design. All other broken lines shown in the figures depict portions of the loudspeaker that form no part of the claimed design.