Hi Wayne,
There's no doubt that the Lexicon MC-12 is an awesome machine, and that lacking processing power was/is never a problem for it 
. Please don't take this as rude but can I request a break from the fawning flattery? Only because it feels awkward at another manufacturer's forum and it isn't really relevant to our nuts-n-bolts oriented discussion. Thanx.
BTW, I mentioned the ability to quadruple the processing power only to indicate that their limited approach to room correction is deliberate and not due to lack of resources.
I'm just left wondering as to why (after the reams of "white papers" that have been written on the subject) that "they are firmly against amplitude based correction"?
I've heard a variety of anecdotal reasons, the main one being to make the most effective use of resources. So they looked at what room problems were best suited to being addressed by electronic means (as opposed to being best addressed by physical treatments). Obvious example: I don't think anyone feels that you can EQ a first reflection away.
Flattening and/or smoothening frequency response is something that can be dealt with using physical treatments or EQ (or, even better, a combination of both). The potential problem with EQ is that an improvement in one seat can result in worse sound at nearby seat, which is rarely the case with physical treatments. So, for this particular problem, it would probably be better start with room treatments and finish off with EQ where treatments aren't as effective (e.g., under 40-60 Hz).
For something like decay time, EQs can be quite effective. Moreso because we're dealing with low frequencies, whose wavelengths are large enough that an improvement at one location will benefit the sound at other locations. And there are other potential advantages: if you have unusually long decay at 37.5 Hz, how do you target that particular frequency with room treatments? So here is a problem where electronic correction can be more effective.
In the thread I linked to earlier, the former chief engineer of Auralex Acoustics said
"decreases in LF decay are often more pleasing to the ear than decreases in LF level. Less muddy tends to be more pleasing than less loud, when given the choice". So if you take three things into account (where are EQ systems more likely to trip up and cause more harm than good; where is electronic room correction most effective in providing benefits; which benefits are more psychoacoustically pleasing to our human hearing), then you'll have three reasons why addressing decay time is a better use of (electronic) resources than flattening frequency response.
It's no wonder then that they limited their correction to decay time and limited the frequencies to the bass region. It was the best bang for the buck, had lesser chance of screwing up, and benefited the widest listening area.
I am not convinced, however, that time-based correction is "more correct" (from the perspective of perception), which is what's really at the heart of this entire discussion.
They weren't interested with correctness as much as they were with perceived improvement. Even if the two improvements are of similar magnitude, decay reduction
sounds better than amplitude reduction.
I've been thinking about this point too, and I'm wondering if maybe their stance on this is based upon wanting to affect the phase of the signals minimally, by introducing as few filters to the signal path as possible?
Part of it is that. Mainly I think it has to do with the problem they're targeting. If they were trying to flatten out frequency repsonse, they may have ended up using all 7 filters per channel. But since they've limited themselves to addressing ringing, they end up using 3 or 4 filters at most, leaving the rest in reserve (over-engineering, typical of Lexicon's studio/pro roots).
Do the products from Meridian, Audyssey and Harman/Kardan also utilize four microphones to derive their measurements?
No, the others all use a single mic. I don't know if Meridian uses multiple locations for measuring, but Audyssey allows you to position the mic at up to 8 different seats for correlation.
Besides a quicker measuring session, there is another advantage to multiple mics over one mic at multiple locations: reliability. The first thing the MC-12 asks the user to do is group the mics as closely as possible for a mic check. The input from the mics is compared and, if one of them is out of spec (relative to the others), the user is alerted and the results of that mic are discarded. With a single mic system, if the mic was bumped during shipping and sent a little out of whack, how would the user ever know? What are the chances of that happening to all the mics? Four mics may seem like overkill for a consumer system but, again, that's their studio/pro background showing through.
If not, I wouldn't consider their products to be "up to the challenge", would you?
I'm not trying to be diplomatic but I think the other EQ systems have their own strengths. For example: the Audyssey system does do some correction above the bass range as well as try to find the crossover point that provides the best blend between your speakers and subwoofers. The other manufacturers might want to look into stuff like that.
H/K does something even more unique. It makes you take 4 measurements: one from your listening seat and one each from the nearfield (literally within two feet) of each front speaker. Measuring from the nearfield allows you to hear what your speaker sounds like
without the room's contributions (at least very minimal contributions).
This gives the EQ system three things to compare: the pure tones in the receiver's signal generator, the sound from the speakers, and what the listener is hearing at the sweet spot. So it knows what your speakers sound like because it can see how the original signal was changed. It also knows what the room added, because it heard the speakers with minimal room contributions.
Aside from some of the stuff we've been discussing, the H/K system uses the EQ as a form of tone control, to subtract some of the room's influence so you hear more of what your speakers actually sound like. Think about that for a moment: instead of using some theoretical ideal, it uses
your particular speakers (warts and all) as a reference point. They're assuming you bought your speakers because you liked how they sounded. Again, I think the other manufaturers we've discussed should at least look at what H/K is doing.
Although it is true that (purportedly) the time-based correction system is capable of correcting frequency-specific time-delay for the entire listening/viewing area with measurements taken from a single microphone/microphone location, it might (to some) seem redundant of Lexicon to recommend the use of four microphones to achieve essentially the same goal, mightn't it?
The
main reason for using multiple mics or multiple measuring locations is to lessen the likelyhood that you are measuring from the null for a particular frequency and therefore not catching its ringing.
BTW, when the 990 first came out, folks asked about room correction. The Outlaws said something to the effect that they hadn't heard a satisfactory auto-EQ system (I'm guessing they meant within their price range). I can understand why they said that. Unless you are willing to license someone else's technology (Audyssey) or have a large research staff (H/K), most of the auto-EQ systems out there aren't going to make a significant improvement to the sound.
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