You can't "trigger" high impedance. The headphones either are or are not high impedance and the phone detects which they are. Most headphones and earbuds will be low impedance. A lot of higher end over ear sets will be high impedance. All most people need to know for the most part is that low impedance headphones require less power to push the headphones. Impedance, by itself, means nothing when it comes to sound quality. Impedance is often why some headsets are louder than others. Also, you will read that higher impedance means higher quality. This is only partially true. The better drivers in headphones normally require more power to push them. That is why people say that. But most sets people will buy will be low impedance. There is a wide range values and quality in low impedance range with some very expensive models still in the low Z category. I sort of wish LG had left that out of setups since so many people with no sound or electronics background look at it like some super magical thing that needs to be on. Nothing could be farther from the truth. It is nothing more than a notification. When I hook it up to my tube amp it tells me I am hooked up to an external device