The AKG K712 Pro headphones are semi-open reference headphones sitting in the middle to upper range of the K series monitor and reference headphones. These headphones improve on the sound from the K240/K701 while still following the same design and feature sets of previous headphones.
The AKGK240 are a cost effective but high quality pair of semi-open monitor headphones. These were my first major purchase when I started out over 15 years ago replacing a cheap set of headphones I had been using for monitoring mixes. Being so young (just 19) at the time I was not really aware of how much of a difference a good pair of cans could make until I put these around my ears.