plate vent holes the size shape location number and placement of the micro vents 225 in the pcb 222 can vary as can the number of micro vents 225 depending on the desired frequency response for the microspeaker the mechanical resistance of the microspeaker in a vacuum manufacturability and other design considerations the acoustical resistance provided to the system by each vent hole depends on its length and diameter u2014 in particular the smaller the diameter the higher the acoustical resistance assuming a fixed length and the longer the hole the higher the acoustical resistance assuming a fixed diameter additionally for substantially identical holes the total acoustical resistance is inversely proportional to the number of holes thus adding holes reduces the total acoustical resistance while removing holes increases the total acoustical resistance as an example for a fixed pcb thickness and thus vent hole length of 360 u03bcm the effect of the acoustical resistance provided by a varying number of holes is shown in fig1 a and 12b for holes of diameter 50 u03bcm and 100 u03bcm respectively in the example of fig1 a and 12b the pcb through which the holes extend has a thickness of about 360 u03bcm the number of holes in each case range from zero to the maximum number of holes that can fit on a pcb of a given dimension and minimum hole to hole spacing in each case the approximate number of holes required for a desired frequency response is noted it can be seen that more vent holes will.