No, just find out how big the circle would be if that kerf's curve continued 360 degrees and made a circle...then do the math for area of that circle and figure out the math from there.
Just view the kerf's as circles and figure out their radius/diameter and simply devide the area up of the circle (usually a quarter of the area) and add/subtract it from/to the volume.
The simplest way to calculate airspace left for the sub would be to just find the dimensions of the enclosure as if they were normal 90 degree corners...and then find out the radius of the circle that the kerf would be, find the area of that circle, devide it by 4, and then subtract that area from the area of the box as if the kerf wasn't there...you then have the amount of space you need to subtract from the total volume as if it were a normal 90-degree box..//content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif