I have spent literally hundreds of hours researching and writing the Guide so that it would be helpful for people trying to calibrate their systems. Unfortunately, it does take some time to read and comprehend what is in there. But, every time I have answered a specific question, you have simply asked another question. That is the reason that everyone has been advising you to read to understand why
we are telling you to do something that way.
I am going to quote a portion of the Guide that actually did answer you last questions. But, I have added a diagram to that section and some additional explanation to make it a little more like cliff notes.
"A second example of the difference between what we hear, and what Audyssey hears, concerns the nature of the omnidirectional Audyssey microphone. The Audyssey microphone hears sounds equally in all directions, but we don't. The pinnae (flaps) in our ears funnel sounds into our ears from the front and from the sides. But, they partly block and deflect sounds coming from behind us. So, early reflections from a wall behind us are going to be noticed far more by the Audyssey microphone, than they are by our ears. And, in trying to over-correct those early reflections, Audyssey may actually contribute to the distortion we hear.
[As a general rule, we don't want Audyssey to become extremely busy in the high-frequency range. Reflections from hard surfaces, bouncing into the Audyssey microphone at close range, can cause Audyssey to set too many control points at high-frequencies, causing additional distortion. The more that we understand why
Audyssey might be doing things to high-frequencies that we don't like, the more that we can enjoy the overall benefits of room correction without adversely affecting our high-frequency sound quality.]
That is why Audyssey advises keeping measurement microphones at least 18" away from a wall or other hard surface. Perhaps an even better example of the difference between the way we hear and the way the microphone hears, involves chair or sofa backs. Most chairs or sofas in our HT's or mixed-use rooms have relatively smooth surfaces. Some of them have fairly firm leather surfaces.
Those smooth or hard surfaces reflect high-frequency sound waves directly into the Audyssey microphone, in a way that they never could if we were actually sitting there. And, the sounds from the back of a sofa would be sufficiently attenuated by our pinnae, and would reach our ears so simultaneously with the direct sound, that we would never hear them. But, the omnidirectional Audyssey microphone would hear them, and in trying to correct something that didn't need correcting, it could introduce comb-filtering (high-frequency distortion) into the sound.
One way to avoid that problem would be to keep the Audyssey microphone at least 18" away from a chair back. But then, we wouldn't be measuring where our ears are, and that could negatively impact our calibration. A better solution is simply to drape a fluffy blanket over our chair backs during calibration. That will enable us to get our microphone within about 4" or 5" of the chair back, and where our ears actually are as we listen. At the same time, that will prevent high-frequency sound waves from bouncing into the mic from very close range. And, Audyssey will leave those spurious high-frequency reflections alone, concentrating its EQ resources on broader areas of the frequency range. (Chris Kyriakakis, the creator of Audyssey, has endorsed this solution.)
Audyssey employs a system of fuzzy-logic weighting to average the results from either six or eight microphone positions (depending on the Audyssey version). In general, I believe that the more we can give Audyssey more consistent measurement results to work with, the more that we can achieve a smoother frequency response, and consequently improved sound quality. This is something that Chris Kyriakakis commented on recently in response to a question. He suggested that the more uniform the sound is within a measurement area, the more uniform the Audyssey EQ is likely to be. The examples above illustrate one aspect of that, but general microphone placement is also a factor.
We typically want to have our microphones at ear level, even if not all of our speakers are at that same height. Keeping the mic at roughly ear level seems to be consistently important. Some users, including myself, have achieved good results by taking just a couple of measurements 2" or 3" above ear level. We typically do not want to go behind a chair back with any of our measurement positions, unless we are deliberately trying to EQ for a second row of listening chairs. And, even then, it would be a good idea to experiment with going behind the MLP, and not going behind it. It helps to recognize that Audyssey is simply trying to EQ a fairly uniform listening area and not individual seats. Other than mic position 1, which is typically centered on the primary listening chair, the mic positions don't need to correspond to actual seats.
It is also a good idea to use a boom microphone stand with an extendable arm for Audyssey calibrations. That allows the base of the stand to remain on the floor. If a tripod is placed in a chair or on a sofa, vibrations from the furniture could be passed up through the Audyssey microphone. Whether that would make a significant difference in the calibration is debatable, but for the small cost involved, I definitely think that it makes sense to use a better and more stable stand than the one that Audyssey provides. The type of stand I am recommending will also provide more exact mic placement and repeatability for calibrations. There are a number of different stands that can work. The one that I am linking below has a built-in microphone holder, which some stands do not.
As a general rule, it is a good idea to measure smaller areas, as opposed to larger areas, for the reasons cited above. We want our measurement area to be large enough to accurately represent the binaural (hearing with both ears simultaneously) nature of our hearing. But we may not want to measure such a large area that we present Audyssey's fuzzy-logic weighting system with too much anomalous information. Patterns that vary in size from as small as about 6-12" out from the MLP (mic position 1), to as large as about 24" to the side and forward are typically used. I would not generally recommend going forward more than about 24" from mic position 1.
It is interesting to note that, in the last couple of years, Audyssey has revised it's owner instruction manuals to recommend a smaller microphone pattern than they used to recommend. They used to recommend 3' to 4' out from the MLP. I believe that they now recommend 2' or less. Their revised recommendations seem to parallel the experience of many Audyssey users, who discovered that smaller microphone patterns often resulted in better sound quality, over a wider area, than large mic patterns did. That is consistent with my own experience, and with that of a number of others on the Audyssey thread.
But, I suspect that finding an optimum microphone pattern is at least somewhat room dependent, so I suggest that interested users experiment in an effort to discover the specific microphone pattern which produces the best sound quality in their rooms. Once they find a mic pattern that they really like, I recommend that they write it down, or draw it, so that they can return to it for future calibrations. Sometimes, fairly subtle differences in microphone placement can yield significant differences in the resulting sound quality.
For people who are looking for some preliminary guidance in selecting microphone positions, the following visual aid is offered. This roughly 2' by 2' pattern is one that a number of people have successfully used. But, it is only shown as a starting point and not as a specific recommendation. People still need to experiment to discover what pattern works best in their particular circumstances.
In this pattern, mic position 1 is about 4" in front of a blanket covered chair, which is the MLP. Positions 2 and 3 are out to each side of 1 by about 12". 4 and 5 are straight out in front of 2 and 3 by about 24". 6 is in a straight line out from 1, about 14" to 18" away. All six of those mic positions are right at ear height (the center of the ear canal). Positions 7 and 8 are in fairly close to the chair back--perhaps about 6" away from the blanket and about 6" out to the side of mic 1. Both of the last two positions are raised up by 2" or 3" above ear level. None of the mic positions go behind the chair.
The specific order of the mic positions is not important. It is only important to keep the mic level (so that it points upward) and close to ear height for at least the first six positions. People who have a version of Audyssey which only uses six mic positions might wish to eliminate 7 and 8 from the diagram shown, or they could experiment with an even more compact configuration for their six. Experimentation is the key to finding a result which pleases the individual user."