One principle of Ambiophonics sound reproduction is that the frontal stage generated by RACE (and optionally enhanced by Envelophonics) should be complemented by concert hall ambience either recorded as a rear pair and reproduced from 4.0 media using RACE in the rear (Panambiophonics) or generated from real concert hall impulse responses. In the case of 2.0 (and most 5.1) media such as LPs and CDs using hall IRs is the only available option. Indeed modern 3D hall impulse responses can be used to produce very natural spatial channels for virtually any number and location of ambience speakers. An impulse response can be thought of as a recording of what happens to a single sample of sound launched from the stage and then bounces around in the rest of the hall.
In the diagram below, AudioMulch a low cost digital audio workstation, and Voxengo (registration payment required for this version) can be combined to produce hall ambience for virtually any number of hall ambience loudspeakers using one ordinary PC or Mac computer. The output is normally via a single USB cable which then needs to be demultiplexed into digital or analog signals for power amplifiers and speakers. At this time such Multichannel Audio Digital Interface (MADI) equipment is only to be found in professional recording engineer catalogs. The RME ADI-6432/MADIface USB is one example of such hardware. Neither the speakers nor the amplifiers need be full range or expensive. Even as few as two is better than none. But the process of creating a domestic concert hall is not for those lacking computer or DIY skills.
Thanks to Prof. Angelo Farina, and Dr. Justus Verhagen, 3D impulse responses are available for La Scala, The Sydney Opera House, and St. Cecilia. These are 96/24 IRs and cover both an entire circle in the horizontal plane and a selection of elevations. Provided below is a set of IRs from St. Cecilia, reverb time 2.2 seconds, for every 15 degrees in a circle at an elevation of 23 degrees but with some at the rear elevated by 60 degrees. So if you put a speaker at 90 degrees to the right you would feed it a right stereo input convolved with the 90 degree IR. The IRs are .wav files and can be loaded into Voxengo which itself is a VST plugin that can be used in many programs. It is not feasible to put the entire set of IRs for all the halls on this site but if you wish additional IRs please send an e-mail to email@example.com