Crown shaping

I have a hat that i am making up as i go along, i casted on 72 stitches and have a 2x2 cable on a 4 stitch reverse background, is there a way to keep the cables in the crown shaping. i was thinking of decreasing out the purls first one at each edge which would be two decrease rows to remove the purl background, but how many plain rows go between the decrease rows.

It really depends on how quickly you want the crown to decrease. If you leave one plain round between decreases, it will, naturally, decrease faster and create a more rounded top. Decreasing more gradually will make a narrower top.

What you could do is determine how many more inches you want for the hat, then measure your row gauge to see how many rows you’ll need to do to get to the top and decrease accordingly.