Special meetings of the Council may be called as provided by ordinance. In the absence of any such provision, special meetings may be called by a vote of Council taken at any regular or special meeting thereof or may be called by the Mayor, or any three members of the Council. The Clerk of Council or in his absence, incapacity or refusal to act, the Mayor shall cause notice in writing of each special meeting to be served personally or to be left at the usual place of residence of each member of the Council not less than twelve hours preceding the time for such special meeting. In the event that a special meeting is called by a vote of Council taken at a regular or special meeting from which any member of Council is absent, written notice of such special meeting need be given only to each absentee in the manner hereinbefore described. Service of notice of any special meeting shall be deemed conclusively to have been waived by any member of Council who shall be present at such special meeting. The matters to be considered at a special meeting shall be stated in the notice required hereinabove, and no other matters may be considered unless this requirement is waived by a vote of not less than five members of the Council.