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發表於 2012-2-11 23:51:59
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Copied from AVS forum to keep the thread alive only, not in a position to translate it, enjoy. 
Room gain is defined by the Athena project at the National Research Council. Anthem used this research when producing ARC.
ARC, or Anthem Room Correction, has been a long time in coming. Its origins can be traced back as far as 1990 to research conducted at Canada's NRC (National Research Council). Under the supervision of Floyd Toole, the NRC had previously performed landmark research into loudspeaker performance. Statistical analysis of controlled listening tests showed that there was a common thread among speakers which subjectively “sound good”: in an anechoic chamber they were the ones which measured a neutral response, free of coloration. This research literally launched companies like Paradigm who, rather than vaguely poking at speaker design, now had a solid definition of what exactly made a good speaker "good".
On the heels of that research came the “Athena” project in 1990. Whereas the previous research looked at many different speakers, Athena looked at only a handful of speakers in many, many different rooms Here again, a common thread was found between what statistics showed to be good sounding rooms. I'll jump ahead just a bit and tell you that it is not what you'd think.
Armed with these data, the next step would be to create a system which could shape the speakers' response to get the system sounding more like the preferred rooms. It was only a matter of time, over 10 years actually, until DSP power in audio processors was up to the challenge, and a filtering system capable of the incredibly complex task could be put into play.
There are two concepts at work here. From some ARC literature:
“What ARC brings to the table is unique: its particular set of audio and room characteristics which their research has shown to be the most significant and “worth” fixing, as well as that what is not and is best left undone. One of the more tangible aspects of this is the concept of room gain, and is one of the target settings you have control over. Room gain is basically the amplitude boost any audio source (be it a speaker or even your own voice) gets in the upper mid-bass range from the boundaries of the room. Filter, or correct for this natural boost, and you end up with an unpleasant, dull sound because our ear-brain just “expects” room gain. ARC assumes you are not using poor speakers and thus when it sees a common “swell” in the frequency response of the measurements, considers that to be room-gain and, here is the key, does not target it for correction the way it does a room mode.”
The "other" concept of room gain has to do with the largest length of the room and its effect on sound pressure when the subwoofer’s radiated frequency is lower than the fundamental resonance of the room, and is distinct from boundary gain:
“The other type of gain is the pressure-vessel gain. Below a certain frequency the room no longer supports standing waves. When the wavelength is greater than the room dimensions, you get a uniform pressurization of the room. You get more gain as frequency decreases so it’s called "room gain". This is more apparent in small tightly sealed environments. Cars are a great example and the pressure vessel gain you get inside that environment is substantial. It occurs lower in frequency and to a lesser extent inside a room. Typical living spaces are not tightly sealed acoustic chambers and their construction varies, giving different results depending on the physical properties of the floor, wall, ceiling, etc… Boundaries that are sturdy and stiff (concrete) give more re-enforcement than does stick-built or flexible building materials that will absorb some of the energy. Think of the Three Little Pigs.”
ARC’s “room gain” will show up at the upper bass/lower mid frequencies. The “other” type of room gain (used throughout the industry) will show up at the low end of the subwoofer’s response chart. There are programs available that model this behavior, but since no room is ideally rigid and lets some sound pressure escape, it can be problematic. The original poster seemed to be puzzled by the room gain effects on his chart. I thought he might have assumed ARC’s “room gain” was the other type utilized in the industry.
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