We claim, the ornamental design for a speaker, as shown and described.
FIG. 1 is the front perspective view of a speaker showing our new design;
FIG. 2 is the front view thereof;
FIG. 3 is the rear view thereof;
FIG. 4 is the left-side view thereof;
FIG. 5 is the right-side view thereof;
FIG. 6 is the top-side plan view thereof;
FIG. 7 is the bottom-side plan view thereof;
FIG. 8 is the front perspective view of the top part of the speaker in use environment;
FIG. 9 is the front view thereof in another arrangement; and,
FIG. 10 is the front view of the two parts in another arrangement.
The dot-dot-dash broken lines seen in FIGS. 3-6 represent the bounds of the claimed design while all other broken lines are included for the purpose of illustrating portions of the speaker; the broken lines form no part of the claimed design.