height of each air distribution chamber such that its cross section constantly decreases as shown in fig2 this is realized in that the front wall 38 facing away from each air distribution chamber 31 32 is obliquely arranged so that each air supply chamber 34 35 extends upward substantially in the shape of a cone fig2 likewise however but not shown it is possible to incline side walls 39 adjacent to each air distribution chamber fig3 so that the air supply chambers 34 35 narrow conically over their length from the bottom upward as is indicated in fig1 by thin lines in the illustrated embodiment each air permeable wall 33 faces an air outflow wall 40 which is also porous the air outflow wall 40 has the same dimensions as air permeable wall 33 and is connected therewith by side walls 41 to form a so called 34 cooling shaft 34 42 subjacent the cooling shaft are so called 34 drop chutes 34 43 which are made tubular each yarn is associated to one tube which is mounted below a corresponding outlet opening 44 for each yarn for cooling the filaments or yarns the air supply channels 37 are supplied with cooling air by means of a blower not shown.