That any municipality shall have power to purchase, improve, erect and maintain public auditoriums, or to authorize the improvement or erection of same by agreement with the officers of the county in which the municipality is located, and shall have power to issue and sell bonds for the purposes herein mentioned. Bonds issued hereunder may be sold by such municipality for cash at one time or from time to time at public or private sale at not less than par. That notwithstanding the provisions of any general, special or local law it shall not be necessary for any governing body of such municipality to submit to the people of such municipality in which said auditorium is proposed to be erected the question as to whether such auditorium shall be erected, nor shall it be necessary to submit to the people of such municipality in which said auditorium is to be erected the issuance of any bonds authorized hereunder to pay for or finance the erection of any such auditorium. Provided, however, that any bonds issued hereunder shall not constitute general obligations of any such municipality, but the payment thereof shall be secured only by a lien against the auditorium and real estate upon which the same is erected and a pledge of the net revenues of said auditorium as hereinafter provided; and provided further that any bonds issued hereunder shall be payable solely and only out of the income derived from the operation of such auditorium and by the property upon which the lien aforesaid is provided.