FIG. 1 illustrates a front-side perspective view of a portable speaker system showing the new design; FIG. 2 illustrates a top-rear perspective view thereof; FIG. 3 illustrates a front elevation view thereof; FIG. 4 illustrates a rear side elevation view thereof; FIG. 5 illustrates a top plan view thereof; FIG. 6 illustrates a bottom plan view thereof; FIG. 7 illustrates a left elevation view thereof; and, FIG. 8 illustrates a right elevation view thereof.