That is not a fact. 19khz is only a frequency, there is no optimal given frequency for any given target. 19k is better for small stuff, like small gold, which is why it is often used for gold machines. It is a tough row to hoe using a gold bug up at the park to try to find coins in the trash, you would be much better off with a f2 or any machine that is not a gold machine. Gold machines typically are not good in iron trash. 19k can be used for any purpose that the circuit designer wishes. A gold machine is totally different than a coin/relic machine, regardless of hertz. For f19 they took 19khz and built a circuit that's designed for relics and coins and such, which are rarely gold. More gold rings have been found with low frequency machines than all gold machines combined. A gold bug will kick f19's arse in finding small gold nuggets because of the circuit, not the hertz. F19 with advanced iron abilities and three tone is not a gold machine, and would be a better choice for relics and coinshooters. If you're in the desert shooting little bitty nuggets, stick with the bugs.