The ornamental design for a portablespeaker, as shown and described.
FIG. 1 is a front perspective view of a portable speaker showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a bottom perspective view thereof.
The broken line showing of the various unshaded elements of the portable speaker is for environmental purposes only and forms no part of the claimed design. The stipple shading represents a matte metallic appearance.