The ornamental design for a soundabsorbingsurface, as shown and described.
FIG. 1 is a perspective view of a sound absorbing surface showing my new design;
FIG. 2 is another perspective view thereof; and,
FIG. 3 is a front elevational view thereof.
The broken lines in FIG. 1 are included for the purpose of illustrating portions of the sound absorbing surface that form no part of the claimed design.