The ornamental design for a microphoneclampplate, as shown and described.
FIG. 1 is a perspective view of a microphone clamp plate showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a side elevational view of one side thereof;
FIG. 4 is a side elevational view of the opposite side thereof;
FIG. 5 is a rear elevational view thereof; and,
FIG. 6 is a front elevational view thereof.
The broken line showings of the bottom boundary, and the left boundary of the cylindrical portion are for illustrative purposes only and form no part of the claimed design.