"In experimental testing, 2.5 kHz (2500 pulses per second) works significantly better than the 30 kHz suggested in Dr. Clark's book. Due to the "skin effect," it can be expected to penetrate more deeply. The skin effect causes high frequency current to travel on the surface of a conductor. In 1995, Clark tested 5 kHz and found it to work better than 30 kHz." ..So I guess the 1khz is more effective.