LEDE/RFZ developed (not how it started out) stands out to me as the better model because of the combination of the ability to hear well into the recorded signal with added spaciousness/development, which is important psycoacosutically.
The audibility and audible effects of early reflections are undoubtedly important, which is why many years ago Sean Olive and I conducted extensive experiments to determine those thresholds.
Olive, S. E. and Toole, F. E. (1989). “The Detection of Reflections in Typical Rooms”, J. Audio Eng. Soc., vol. 37, pp. 539-553.
The abstract is:
“Reflected sounds influence the timbre and spatial character of live and reproduced
sounds. Most investigations of reflections have focused on the performance of live
sounds in large halls. Current interest in the acoustical interactions of rooms, loudspeakers,
and listeners requires further and possibly more relevant data than have been
available. In this study, the effects of reflected sounds were examined as they would
occur in stereophonic reproduction in rooms of domestic or control-room size. Thresholds
were determined as a function of level relative to the direct sound, the angle of incidence,
spectrum, the temporal form of the signal, and reverberation. The relationships between
audible effects and measurements, such as energy-time curves and frequency response,
are discussed.”
If you read this, and some of the data from it repeated in my books (Chapter 6 in the 4th edtion), it is evident that common interpretations of the Haas effect, Haas kickers, the effect of additional reflections, etc. are simplistic or wrong. The widely assumed “fusion zone” of 30 ms applies only to speech in an anechoic environment, yet it gets trotted out for numerous applications involving music in rooms. Few people have taken the trouble to understand the established science, and persist in perpetuating old school notions.
And Don Davis wrote further:
"The LEDE technique, by virtue of the distance the direct sound must travel to encounter a first reflection, adjusts the initial time delay gap to the same figure that Beranek judged as desirable in the best concert halls, namely 20 ms. It is no coincidence that the same 20 ms is the optimum delay for the maximum Haas effect in good, diffuse, semi-reverberant spaces."
This confuses a number of things. Concert halls
need diffusion to convey the orchestral energy to all parts of a widely distributed audience. What is heard in a concert hall is a complex comb filter that is very pleasant, but mostly for those who can afford the good seats. Not all reflectied sounds are perceived the same way. The reflected sounds that create the desired envelopment arrive after delays of 60-80 ms and more, arriving from about 60 deg (in the good seats), not 20 ms arriving from the rear in a LEDE room. As shown in the above paper and in my books the precedence (Haas) effect is very different for different sounds, and it changes enormously with the addition of reflected sounds whether they are in the room or in the recording. There are no “single number” generalized solutions. The Haas "kicker" is a based on a significant misinterpretation of published literature, as was tested in the above paper.
Diffusion of the sound field in listening rooms is of no benefit. In fact, if too energetic and from the wrong direction it degrades the delivery of directional and spatial information encoded in the stereo recording. Reflected sounds arriving from the sides are most effective in creating impressions of space - that is how the binaural hearing system works. Even a single synthesized reflection from the side in an anechoic chamber is perceived as "spaciousness" not comb filtering. Humans are programmed that way.
Diffusers in small rooms should be used to attenuate reflections by sending most of the energy off in other – hopefully non-destructive – directions. However, the energy remains in the room, which may not be an advantage. The performance of diffusers that matters most in small rooms is how they alter the attenuated sound reflected in the direction of the listener, a performance factor that is rarely specified. The gratings cause spectrum changes and phase shifts in the reflected sound. Fortunately humans are not sensitive to phase shifts, and the magnitudes are trivial compared to the delays involved, but the spectrum changes in some diffusers are significant. Peter D'Antonio has discussed this and published some data.
I greatly prefer all early reflections attenuated strongly as the contribution is only negative IMO. Something I often ask myself is whether such studies are able to show us what listeners experience over time. Perhaps a short listening session with mainly high quality recordings do not reveal that well what we experience for longer listening sessions and with variation in music material.
I find traditional stereo often lacking in spaciosness. The use of lateral reflections increases it, but IMO leads to tonal variations and listening fatigue with especially poor recordings. Even with quality speakers with a uniform directivity. Multiple speakers add more lobing, comb filtering, increase high gain early reflections unless extensive use of absorption, and while it adds spaciousness it's more a chaotic mess and deviates a lot from accuracy with quite poor imaging.
A well designed modern diffuser on the hand, and as long used correctly (for late arriving reflections) removes much of the negative contribution from reflected surfaces and adds the very much needed spaciousness.
I understand that you are in the business of selling acoustical devices, and I hope your business prospers, but what is stated in this quote are your personal opinions - subjectivity.
I have my opinions too, but from the time I began my research in 1966 I have used the opinions of others, hundreds of them in controlled experiments to focus attention on specific variables. The accumulated data provide a basis for understanding the relationship between what is measured and heard. A single omni mic in a room is not the same as two ears and a brain, and raw ETCs are spectrum blind, not providing the necessary information to assess the audibility of reflections or the multitudes included in diffuse sound fields. The final answers to all questions are not yet discerned, but a genuine scientific approach is needed to clarify those remaining.
In the meantime, so long as recording engineers listen in circumstances that please themselves as individuals the opportunity for the recorded art to transfer to the listener in typical domestic rooms will remain a lottery. An extreme example of this is described in Section 12.5.5 in the 4th edition, where Blackbird Studio C is described and discussed. The design goal for this extravagantly expensive space was to provide George Massenburg, an influential recording engineer, with a wide sweet spot and an acoustically immersive experience. Peter D'Antonio, a genuine expert on diffusers, designed a room with all surfaces covered with 1 m deep broadband 2D diffusers. Sadly, after the effort and expense no new knowledge appears to have emerged. Recording engineers apparently adapted to the unique sensations of the room, and it was (is?) used as an Atmos mix room. Whatever is heard in this room it is not replicated in any audiophile listening space - the ultimate target audience - much less in the rooms occupied by masses of everyday audio enthusiasts, who should be the target.
The widespread use of near-field listening, with or without acoustically dead, reflection eliminated rooms is the extreme opposite of the Blackbird studio. The middle ground is occupied by countless variations.
Recordings need to work in ordinary rooms or they miss the target audience. Now that most listening is done using headphones that argument becomes a somewhat academic question.
At least there are strong indications that monitor loudspeakers have moved in the direction of "high fidelity", neutrality, technical accuracy. This aspect of the circle of confusion is showing signs of rationality.
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