The board shall hold not less than twelve (12) regular meetings each year, on a day of each month as the board shall determine, unless a legal holiday, then on the next ensuing business day, for the purpose of transacting business as may come before it. The chairman of the board shall preside over all meetings, except that he shall only be permitted to vote in the case of a tie vote. In the absence of the chairman, the vice chairman shall preside over meetings, except that he shall have full voting privileges. Additional regular meetings may be held as the board shall determine in its by-laws, rules and regulations. Special meetings of the board may be called at any time and from time to time by four (4) members of the board, and on the written request of the director, showing the necessity and purpose for a meeting. The board chairman may call a special meeting specifying the time, place and purpose of the meeting. The secretary shall cause due notice to be given to each member, either personally or by telephone, mail or telegraph, of the time, place and purpose of all special and regular meetings, and upon his failure so to do, notice may be given either by the chairman or the four (4) members concurring in calling any meeting. Any meeting of the board at which all of the members are present shall be as valid as if held pursuant to proper notice, and should a meeting be held without notice when all members are not present, if the absent member or members shall have signed a waiver, or shall subsequently sign the minutes of the meeting, it shall be as valid and binding as though called upon due notice. A majority of the members of the board shall constitute a quorum and a majority of all members of the board shall be necessary for the authorization of any act by the board, except as otherwise herein provided.