The first of the third party IR libraries I'm going to look at comes from Ernest Cholakis, who will already be well known to many musicians for his creation of the DNA Groove Templates. He has been exploring reverberation impulse responses for the last ten years, and has already released sampling CDs using this extensive knowledge, including the acclaimed Drone Archeology (reviewed in SOS December 2002)...
Using his own extensive recordings of spaces such as concert halls, cathedrals monasteries, and even the ambience inside the Great Pyramid Kufu at Giza, Ernest has re-synthesised the impulse responses in the Pure Space libraries, which means the results suffer from none of the limitations of real-world recordings -- for instance, because of the way Ernest generates his responses, the 24-bit versions offer a dynamic range of more than 140db, while their frequency responses are virtually flat, so you can EQ your sources to taste before convolving them...
Using his own extensive recordings of spaces such as concert halls, cathedrals monasteries, and even the ambience inside the Great Pyramid Kufu at Giza, Ernest has re-synthesised the impulse responses in the Pure Space libraries, which means the results suffer from none of the limitations of real-world recordings -- for instance, because of the way Ernest generates his responses, the 24-bit versions offer a dynamic range of more than 140db, while their frequency responses are virtually flat, so you can EQ your sources to taste before convolving them...