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 a rear perspective view thereof; and,
FIG. 9 is an enlarged front perspective view of the portion 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 a portion of the claimed design that is illustrated in an enlargement and form no part of the claimed design.