Any investigation, inquiry, or hearing which the Commission has power to undertake or hold may be undertaken or held by or before any one or more of the commissioners, upon condition, however, that such commissioner or commissioners shall have been authorized by the Commission to undertake or hold such investigation, inquiry, or hearing. Any determination, ruling, or order of a commissioner or commissioners, upon any such investigation, inquiry or hearing, shall not become effective until due notice has been given to the Commission and has been approved and confirmed by at least a quorum of the Commission and ordered to be filed in its office; provided, that any such determination involving the fixing or regulation of general schedule of rates shall not become effective until due notice has been given the radio common carrier concerned and an opportunity has been given such carrier to be heard before, and the same has been approved and confirmed by, at least a quorum of the Commission. Upon such confirmation and order, such determination, ruling or order shall be the determination, ruling or order of the Commission. In any investigation, inquiry, or hearing now pending or which may hereafter be instituted, the Commission is hereby authorized to employ a special agent or examiner who shall have power to administer oaths, examine witnesses, and receive evidence in any locality which the Commission, having regard to the public convenience and the proper discharge of its functions and duties, may designate. The testimony and evidence so taken or received shall have the same force and effect as if taken or received by the Commission, or any one or more of the commissioners as above provided.