The ornamental design for a loudspeaker, as shown and described.
FIG. 1 is a front elevational view of the loud speaker;
FIG. 2 is a rear elevational view of the loud speaker;
FIG. 3 is a top plan view of the loud speaker;
FIG. 4 is a bottom plan view of the loud speaker;
FIG. 5 is a perspective view of the loud speaker; and,
FIG. 6 is a left side elevational view of the loud speaker, the opposite side being a mirror image thereto with the exception of the different unclaimed environment as seen in FIG. 2.
The broken lines shown are included for the purpose of illustrating the unclaimed portions of the article and form no part of the claimed design.