CSO management put a brave face on the 1966 renovation of Orchestra Hall, but as I recall the reaction of the majority of the public was one of shock and a feeling of great loss. I don't know what management thought themselves, but it wasn't many years before work was done to try to repair some of the sonic damage. Further efforts followed, most significantly around 1997. It's a little better. At least fortissimi really get loud again rather than seeming to be cut off by a limiter, there's again a semblance of tone in the strings, and one can hear the basses again. All of that was ruined in 1966, along with any semblance of "air" around the sound. Regarding the installation of air conditioning in old buildings, in addition to what Steve Smolian wrote there was also the issue of the low-level noise that older systems caused. By 1966 that had been resolved well enough to permit its installation. Don Tait