The ornamental design for a loudspeaker, as shown and described.
FIG. 1 is a top perspective view of a loudspeaker showing the new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a side elevational view thereof;
FIG. 5 is an opposite side elevational view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a side elevation view thereof, shown without the environmental loudspeaker for ease of illustration.
The broken lines illustrate portions of the loudspeaker that form no part of the claimed design. The broken lines loudspeaker in the figures illustrates environmental subject matter that forms no part of the claimed design.