The ornamental design for a loudspeaker, as shown and described.
FIG. 1 is a perspective view of embodiment one, of a loudspeaker, showing our new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a side elevational view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a perspective view of embodiment two, of a loudspeaker, showing our new design;
FIG. 6 is a front elevational view thereof;
FIG. 7 is a side elevational view thereof; and,
FIG. 8 is a top plan view thereof.
The broken line portions show unclaimed subject matter only and form no part of the claimed design. The dot-dash broken line portions are included to show the boundary between the claimed portion and unclaimed portion only and form no part of the claimed design.