Its not your fault Adrian you did nothing wrong. My Denon manual says to adjust the sub to the half way point as a starting point, however not all subwoofers are the same. In your case it is too high and on other subs that would be too low. Some are really sensitive and need little gain adjustment on the sub and receiver and others need a much higher voltage sent to them to perform properly. I always strive for a setting close to 0 give or take.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne