The ornamental design for a speaker, as shown and described.
FIG. 1 is a front perspective view of a speaker showing our new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is an enlarged front perspective view of the portion 8 encircled in FIG. 1; and,
FIG. 9 is an enlarged front perspective view of the portion 9 encircled in FIG. 1.
The dashed broken lines in the drawings illustrate portions of the speaker that form no part of the claimed design.
The dot-dash broken lines in the drawings encircle portions of the claimed design that are illustrated in enlargements and form no part of the claimed design.