Actually, I've been doing some amount of research regarding the Linkwitz theory and other theories regarding small rooms. I think what Linkwitz is saying is that the dipole effect for frequencies under 200Hz minimizes interaction with room modes. I think he's right. He's not saying that room modes cease to exist because of his speakers, but that his speakers limit interaction with those modes. If you look at many of the subwoofer placement articles, they do the same thing -- place the subs in multiple locations in order to "even" out the interaction with room modes -- decrease the SPL of peaks and increase the SPL nulls.
As for above 200 Hz, Linkwitz recommends RT60 times that are a bit higher than what others recommend (depending on whom you ask, that is). But it's not shockingly higher and does contribute to the reflections. The common conception is that reflections are evil, but this conception does not jive for reality. For instance, many open baffle speakers are loved (remember Eric, who went from RMXs to what was essentially an open baffle speaker for certain frequency ranges, and liked the other speaker better?). As for reflections, this is a very complex part of a room, and it's truly little understood. Here are some quotes from "Loudspeakers and Rooms for Sound Reproduction—A Scientific Review", by FLOYD E. TOOLE, J. of the Audio Engineering Society, vol. 54, no. 6 (June, 2006):
"The single-channel, hard-panned signal of a news reader
is perceived as originating in the center-channel loudspeaker
localized within the listening room; the loudspeaker
itself is the real source of sound. If spatial cues, in
the form of real or simulated reflections, are incorporated
into a good multichannel recording, they can make the
loudspeakers less obvious and can cause the apparent
sound source to seem farther away and the room to seem
larger. A psychoacoustic perspective on what is happening
in these instances would be able to indicate the characteristics
of both local and recorded early reflections necessary
to establish dominance in our perception of distance.
Hints that the perception of distance is more driven by
monaural cues than binaural cues [27] are encouraging,
given the limited number of channels available in our audio
systems. However, if there is even an element of
“plausibility” in distance perception, it may be difficult not
to be influenced by walls and loudspeakers that we can
see. More research is needed on this important topic." Page 458.
"The precedence effect will guide our attention to the
first arrived sound as an indicator of the location of the
source. However, early reflections can cause this directional
impression to shift slightly, or the “image” of the
source to be enlarged. One can logically speculate that the
image shifting or spreading is associated with a reduction
in interaural cross correlation (IACC), in the well-known
tradeoff with spaciousness—increasing spaciousness tends
to be correlated with image broadening [30]. Haas noted
that adding a delayed lateral sound caused a “pleasant
broadening of the primary sound source” [31]. Olive and
Toole determined the delays and levels at which a single
lateral reflection caused a perceptible change in the size or
location of the primary image [32]." Page 459
As for reflections, in section 2.5, "Effects on Timbre -- Comb Filtering, Repitition Pitch", he states:
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"The acoustical sum of a sound and a delayed version of
the same sound produces two results. First, if measured, it
yields a frequency response that looks a bit like a comb,
with regularly spaced alternating (constructive interference)
peaks and (destructive interference) dips. Second, if
listened to, we can get any of several responses, including
coloration at worst and a pleasant sense of spaciousness at
best. In that sense, comb filtering is something akin to a
measurement artifact.
The worst situation is when the summation occurs in the
electrical signal path or within the loudspeaker itself. Then
the direct sound and all reflected versions of it contain the
same interference pattern. Another difficult situation is
one with only a single dominant reflection arriving from
close to the same direction as the direct sound. In a control-
room context, this could be a console reflection in an
otherwise dead room.
Fortunately such events are rare. Most reflections arrive
from directions different from the direct sound, and perceptions
vary considerably. Two ears and a brain have
advantages over a microphone and an analyzer. The fact
that the perceived spectrum is the result of a central (brain)
summation of the slightly different spectra at the two ears
attenuates the potential coloration from lateral reflections
significantly [34]. If there are many reflections, from
many directions, the coloration may disappear altogether
[35], a conclusion to which we can all attest through our
experiences listening in the elaborate comb filters called
concert halls. Blauert summarizes: “Clearly, then, the auditory
system possesses the ability, in binaural hearing, to
disregard certain linear distortions of the ear input signals
in forming the timbre of the auditory event” [6].
Superimposed on all of this is a cognitive learning effect,
a form of “spectral compensation” wherein listeners
appear to be able to adapt to these situations, and to hear
“through and around” reflections to perceive the true nature
of the sound source [36]–[38]. Put differently, it
seems humans have some ability to separate a spectrum
that is changing (the program) from one that is stationary
(the transmission channel/propagation path). It is evident
that we do not yet have all the answers, but it seems clear
that the human auditory system is well adapted to dealing
with reflective listening spaces.
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As you can see, reflections are necessarily good or bad. The article is quite long and is worthwhile reading.
