Machined and a well designed magnetic gap with good flux geometry that is not so wide that it is like throwing a hotdog down a hallway. Can't have a shit frame with a tight gap... If you so much as do not torque some pro drivers correctly WITH MACHINE SCREWS it will warp even a machined or cast frame, the VC will rub and it will fucker the driver.. I have a JBL1500GTi that got fuckereed that way... drywall screws ruined it.