I don't want to create any controversy here. People are perfectly free to either like or dislike the surround boost as they choose. But I wrote something about the surround boost back in January (page 2626 of the old thread) that I think might be worth repeating in this context.
"I wanted to write a somewhat lengthy post on DEQ, based in part on the excellent dialogue with Chris that Feri posted yesterday. The issue that they were discussing was the original intent of the surround boost in DEQ, and how it was implemented. The conventional wisdom on this thread has been that the surround boost was, at least in part, based on a misconception regarding sound falling-off faster from behind us than it does from in front of us. But, I think that the issues with the surround boost go deeper than that. With apologies to all, I think that the concept of the surround boost, as a part of DEQ, had some logical flaws from the very beginning. And the fact that so many people notice that their surrounds are boosted, with respect to their front speakers, is an inevitable result of those flaws.
Before I discuss what I am calling flaws in the concept, however, I want to make something very clear to anyone reading this who is less familiar with Audyssey. Audyssey the room EQ system (in whatever generation of version: including 2EQ, MultiEQ, XT, or XT-32) is a very effective automated room correction system, which simply attempts to reduce distortion caused by the interaction between speakers and room. Additional Audyssey features, such as the Reference Curve (with MRC), Flat, DEQ, and Dynamic Volume, are features which are at least somewhat distinct (particularly the last two) from the room correction software. They are user preference features, much like the built-in apps on a smart phone. So, nothing that I am saying about the surround boost in DEQ should be taken as criticism of the basic EQ software. Audyssey is capable of doing an outstanding job of EQing a room. It is only in implementing the user preference features that go on top of the EQ, that people may generally find fault with one or another of the apps.
According to Chris, as stated on many occasions, the original reason that Audyssey included a surround boost with DEQ is because sounds arriving from the rear fall-off faster than sounds arriving from the front. In the discussion Feri quoted, Chris explained that Audyssey's research indicated that the pinnae of the ear (the visible part attached to the head) partially block sounds above about 1000Hz from reaching the ear. I have several problems with this conclusion. Among them is the absence of other research confirming this. As a practical matter, I also think of all the species of dogs with large flaps completely covering their ears who hear very well into ultrasonic frequencies. If higher pitched sounds are less audible from behind (due to our pinnae) than lower pitched sounds, then the higher the sound, the greater the attenuation, and that just doesn't seem to be borne out by practical experience, or by other research. But, let that go for a moment. Let's assume for a moment, that the intent of the surround boost was valid. In that case, I have several problems with the fundamental concept of how it was to be implemented.
First. If the problem is the pinnae of our ears partly blocking sounds arriving from the rear, what does that have to do with sounds from the rear falling away faster than sounds from the front? That question was pointed out several years ago, and it still seems like a valid question to me. Somewhere in there, a conceptual leap was made between the idea of the pinnae blocking high frequency sounds, to sound from the rear falling away faster, and there is nothing whatsoever to justify that conceptual leap. To me, that is an inherent flaw in the concept that affected the subsequent implementation.
Second. If the problem is either rear arriving sounds falling away faster in the higher frequencies, or simply being attenuated to start with in the higher frequencies, what does that have to do with surround speakers which are typically located more or less out to the sides? What application would a surround boost have in a typical 5.1 system, which at the time the technology was introduced, included the vast majority of systems? Only where rear speakers are employed would the pinnae of the ears be a significant factor in blocking higher frequencies in the typical system. But the surround boost was, at the time, primarily for speakers out to the sides.
Third. If the pinnae in our ears really do block higher frequencies, why wouldn't it simply be better to boost the surrounds from the outset? Even at Reference levels, high frequency sounds arriving from the rear would be perceptually lower than front, or side arriving sounds, if the theory were correct. So, we would always need to have our rear (not side) surrounds boosted in order to hear high frequencies comparably. There is that pesky conceptual leap again from pinnae blocking high frequencies from the rear, to rear arriving sounds decline faster than front arriving sounds. That conceptual leap led them down a bad path, in my opinion.
Fourth. Let's say that none of the other logical flaws existed. For the sake of discussion, let's assume that we really do want to amplify higher frequencies arriving from both the side (where the pinnae don't block them) and from the rear where they might. Even so, there was still a flaw, in my opinion, in tying that desired frequency boost to DEQ. And that's because the stated purpose of DEQ is to maintain equilibrium in the full frequency range, at below Reference volumes. So, a high frequency boost, and a low frequency boost are applied, while the mid-range is left unaffected, on the assumption that our hearing is most sensitive in the mid-range, and that as volume goes down, we need to amplify high and low frequencies to maintain an acoustical balance with the mid-range. And yet, it was the mid-range where Audyssey said their research showed that we started to need a boost--at about 1000Hz. So, doing both a high and low frequency boost, while leaving the mid-range unaffected, wouldn't actually solve the problem they posited. Attaching the surround boost onto the more valid DEQ application was always a kludge.
In some respects, this might have been the biggest logical flaw of all, because the most notable feature of DEQ is the bass boost. So, boosting the surrounds globally, at the same time that you are boosting the bass (DEQ's treble boost is much less perceptible) simply calls even more attention to the surrounds, when the original intent was only to restore some balance in the higher frequencies, so that those higher frequencies arriving from the rear would balance with those arriving from the front. But what we actually hear from back there is much lower frequency sound than that, since the surround boost is implemented in conjunction with DEQ, which most noticeably boosts bass. And for many people, that merely draws unwanted attention to the surrounds. So, they didn't really solve the problem they set out to solve. They just called more attention to the surrounds.
If I seem unduly hard on Audyssey in this post, I don't mean it that way. But bad assumptions have a way of accumulating, and I think they started this process of a surround boost with good intentions, but flawed logic. Of course, there are workarounds, so we can have our cake and eat it too. For people who are using DEQ for everything, if the surround boost bothers you, you can easily reduce your surround trims to a comfortable level (typically about 3db). It's a little more problematical if you are using DEQ more randomly, although I have never really minded adjusting trim levels when necessary. Or, of course, you can leave DEQ off, and explore other ways to achieve more bass at lower than Reference volumes. But I wanted to get some thoughts about the surround boost down on paper, since the issue comes up so often."
GUIDE TO SUBWOOFER CALIBRATION AND BASS PREFERENCES
* The Guide linked above is a comprehensive guide to Audio & HT systems, including:
Speaker placements & Room treatments; HT calibration & Room EQ; Room gain; Bass
Preferences; Subwoofer Buyer's Guide: Sealed/ported; ID subs; Subwoofer placement.