How to correctly mute a subwoofer enclosure for optimal performance ?

well, you should have the correct volume for "each speaker". Your speakers should have come with box size requirements. to do this correctly you will need this info. Base X Height X Width is your formula. Base or depth is the distance from the front to back. height is distance from top to bottom and width is from side to side. you will want to get your handy tape measurer and measure the inside dimensions. If your box has the inside dimensions of 2' X 2' x 2', your box has a volume of 8 cu. ft. Each of your 12'' speakers my require a volume of atleast 4cu.ft. if this is true then the 8 cu. ft box would work. In the end you may just have to use only 1 speaker for your box. The polyfill is to help keep the air waves separated from each speaker if I recall which wouldn't be needed if the box was built with divider or partition. Someone may correct me on this . Hope this helps