Designed for use with the C5 unit, the deep field coils require 2 synchronized outputs per set.  They will not work with individual pulse generators (such as the A9 or M1).  You can use 2 sets of deep field coils on a single C5.  The coils are just 2 pairs of standard coils that we stack and tape into the side-by-side configuration.  We measure and verify the correct polarity to get maximum effect.  It is critical to align the coil polarity properly in the assembly, so we provide this as a service.  This gives you about 60% more peak power and more depth of penetration of field.  This is for the special case where very deep tissues need to be stimulated at high power levels, such as hip joints.