Tom Hidley did pioneering work and established the fundamentals behind the 'Non Environment' or 'hemi-anechoic' control room. Simply put, the room is very highly damped down to the lowest frequencies. Large loudspeakers are (usually) flush mounted in the hard front wall, thereby making them 'infinite baffle' systems that are impervious to reflections from the front wall. The only reflections come from the hard floor, which, along with the front wall, provide the liveliness necessary for comfortable human communication. 

There was a period, from the early 70s, up to the late 80s, which many refer to as 'The Golden age of Audio'. The industry was at its commercial, creative and technological peak. The big studio business was largely legitimate, and music making was usually handled by seasoned professionals. It was in this environment that the 'Non Environment' room thrived. However, to build such a room at the time, over 4' of space was necessary behind each surface, for acoustic treatments. This became unfeasible in the 90s and later, when real estate became much more dear, and eventually, small project studios started handling a chunk of the business. The Non Environment as envisioned by Hidley and Newell became less popular, albeit with a few staunch believers. 

However, thanks to more recent research conducted separately by the BBC and Dr. Helmut Fuchs at the Fraunhofer Institute, it has been shown that steel sheets, when used appropriately, can make exceptional bass absorbers. It is now possible to create rooms with 'Non Environment' characteristics, while taking up only 9" of space for acoustic treatments on the walls and ceiling.

By default, the Control Rooms I build today conform to this ideal. I have built a tiny room (<10 sq. mt.), and relatively large ones (>30 sq. mt.), and they sound remarkably similar. What can be heard is what the speakers put out, with very little colouration due to the room.