A lot of time rippers are used to get under the hard pan. The hard pan will happen are different depths depending on soil structures. My fields hard pan between 12 and 16” most of the time; I have a lower field that hard pans at about 8”. I have been told in some states the hard pan is around 20 to 30".
The rippers that are used around us are mostly 2 shank (centered at the
tractor tires) and they will have a small wing or a ball and chain. The wing will lift the lower layer of soil leaving an air space and will fracture more of the hard pan if the wing is under the hard pan. Not many people use the old ball and chain, but it will leave a air space and if the ball is under the hard pan it will also fracture the hard pan.
When ripping it's best to rip at a 45* angle of the row crops or to the direction of traffic. This is leave less compaction to the the hard pan that was fractured when driving on the fields.
There are also rippers that are used in no or low tilling, but most of the time they will be used with other tools. With no till the rippers are set to about 3” and will be about 3 to 5” apart. Most of the time disks will be on the same frame as the rippers and sometimes other stuff to get ready of a seed drill.