I'd listen to sharper guy and change your technique, rather than your headphones. Frequencies under 20hz are frequencies you can feel, rather than hear, so they shouldn't be something to be concerned about.

Those headphones should work just fine, I assume i-doser works with the frequencies we can hear, and those headphones can reproduce frequencies from 21hz to 18khz, that's a very good range, as humans can only hear frequencies from 20hz to 20 khz. It's not in English, but from what I see it only go's...