I claim the ornamental design for a speaker clock, as shown and described.
FIG. 1 is a front perspective view of a speaker clock, showing the new design;
FIG. 2 is a front elevational view of FIG. 1;
FIG. 3 is a rear elevational view of FIG. 1;
FIG. 4 is a left-side elevational view of FIG. 1, the right-side elevational view being a mirror image thereof;
FIG. 5 is a top plan view of FIG. 1;
FIG. 6 is a bottom plan view of FIG. 1; and,
FIG. 7 is a rear perspective view of FIG. 1.
The broken lines representing digital illuminated numbers in FIGS. 1 and 2, and device controls in FIGS. 1, 3 and 5, and a logo in FIGS. 1, 3, 5 and 7 form no part of the claimed design.