We claim an ornamental design for an audio speaker, as shown and described.
FIG. 1 is a perspective view showing the claimed design;
FIG. 2 is a second perspective view of FIG. 1;
FIG. 3 is a third perspective view of FIG. 1;
FIG. 4 is a front elevational view of FIG. 1;
FIG. 5 is a rear elevational view of FIG. 1;
FIG. 6 is a left side elevational view of FIG. 1; the right side elevational view being a mirror image of FIG. 6;
FIG. 7 is a top plan view of FIG. 1;
FIG. 8 is a bottom plan view of FIG. 1;
FIG. 9 is a perspective view showing the claimed design in an opening usage state;
FIG. 10 is a reference view of the claimed design in the opening usage state which is used to accommodate a pair of microphones; and,
FIG. 11 is another reference view of the claimed design in the opening usage state which is used to accommodate a pair of microphones together with a mobile phone.
The broken lines in the figures represent portions of the article which form no part of the claimed design.