Dirty voice coils cause overheating and makes speaker response slower. When your cleaning a Black Widow coil gap take a business card and cut it small about and inch and a half, now get some double face tape, quarter or half inch wide, tape it to one end of the business card just on one side and run it around the voice coil gap. Masking tape is to wide for Black Widows. Keep doing it till it becomes clean. Keep changing the tape till its clean.