The problem with Alpine is their slot port volume specs are different than their tube port volume specs by quite a bit, at least for the new type R's. Normally, you just have to take the radius of the tube port, in this case 1.5", square it and multiply by Pi( 3.1415). This yields, 7.068 square inches of port face x the length= 70.68 cubic inches of port volume. You then divide that by your slot port dimensions. eg. 70.68/11(port height)=6.42/1(port width)=6.42 which equals your port length. This will give you the same mass of air to move in your port and should give you the same tuning as the round tube port. Unfortunatly, Alpine has not specified a slot port for these subs, but they do for the new models, and the slot and round volumes are very different.