It is quite easy, when one sits in the front half of the audience at an unamplified concert of classical music to hear that "depth of stage" is caused by the amount of added reverberation one hears around the direct sound from musicians further back on the stage compared to those in front. This is true even if the musicians in the back have greater brilliance to their direct sound, such as trumpets playing in their high register--they still sound further back.
I find that the
Dutch & Dutch 8c speakers I currently use reveal more clearly than any other speakers I've owned the difference in the amount of recorded ambiance accompanying the direct sound of instruments further back on the stage. This contributes to a life-like depth of field perception, one that closely mimics what I hear live at a concert from the first few rows, even though myD&D speakers are located quite close to the wall behind them. This ambience is more "attached" to the direct sound of each instrument than with other speakers. Whether this is due to the dispersion characteristics of the speakers, their time alignment, or some other factor, I don't know.
I really think whether audiophiles prefer reflective or absorptive listening room surfaces comes down to whether they want to create a "you are there" or a "they are here" space at home. I am clearly in the "you are there" camp. To get the "you are there" feeling, you must suppress the surface reflections of your small listening room to fully reveal whatever larger venue acoustics are captured on the recording. You must suppress the "second venue" effect of your listening room's small room acoustics overlaying the concert hall acoustics captured on the recording. This demands either absorption or at least diffusion of specular reflection areas of all listening room surfaces, even those behind the listener.
I also think, however, that a great many recordings, even classical music recordings, don't contain enough recording venue ambiance to well construct a "you are there" feeling of envelopment. I think that a lot of recording engineers do this on purpose, supposing, as Toole does, that most listeners will leave their listening room surfaces untreated and that this will add space and ambience. It may well do that, but it is the wrong kind of space and ambience, a type which uniformly gets added to all recorded material and which to the astute listener just doesn't sound real in the "you are there" sense. It may contribute to a "they are here" feel, however, and some listeners may feel that's preferable, at least for some types of music other than classical. Actually, I think many listeners prefer "they are here" for most music. And without extra channels, with dry recordings many listeners may prefer the listening room's reflections to no reflections with dry recordings. That may be what is behind Toole's findings of listener preference for reflective surfaces in listening rooms.
But besides revealing the ambient cues actually on the recording (the "you are there" feeling), damping the listening room's surfaces also gets rid of obnoxious brightness from highs splashing off surfaces where the reflection time is delayed less than 10 or 20 ms. Thus, while damping some room surfaces may not improve imaging/staging much, damping them removes the excess brightness. This is especially true in small rooms like mine for the reflections from the nearest side wall.
I believe that controlling dispersion is helpful for both imaging and reducing spurious brightness. In my small room, the Dutch & Dutch 8c dispersion characteristics seem just about perfect. There is much less spurious brightness and better imaging and staging with these speakers before any room treatment is added than with any other speakers I've had in this small room. Yes, adding the absorption and diffusion makes a positive difference, but the difference is not night and day as it is with most speakers.
Some serious acoustic research, such as the Archimedes Project of the 1990s, found that thr floor reflection is the one most seriously affecting the imaging capabilities of speakers. While a heavy carpet is quite helpful in damping the floor reflection at frequencies above 2 kHz (the main band found to most affect imaging in this study), my own experiments over the decades have convinced me that with most speakers, adding a thick layer of foam absorption over the heavy carpeting can further improve imaging and staging, helping the speakers disappear as sound sources. Most audiophiles do not further treat the floor reflection, however. One simple reason is the lack of practicality. Putting foam absorption on the floor creates an obvious trip hazard in the room since the foam usually needs to be placed between the speakers and the listening seat, fairly close to the listening seat.
Someone proposed an "audiophile coffee table," one whose soft foam surface is raised from the floor by legs, avoiding the trip hazard. This is an idea worth exploring. I've never tried it.
I have a feeling, however, that such an "audiophile coffee table" will not sound as fine as putting the absorption/diffusion on the room surfaces. I've found in experiments over the years that putting bits of absorption very close to speakers just doesn't sound as good as putting more of it on the walls, floor, and ceiling. Speakers tend to sound "small," "closed down," and lack "openness" when I've placed textured or flat foam very near the back, sides, or top of speakers. I have made homemade versions of the old
Watkins Echo Muffs (if you remember those) and they just don't sound the same as putting more foam at a greater distance from the drivers. Thus, I don't hold out too much hope that putting the foam atop a table will sound as fine as putting it right on the floor. But I agree it's worth a try; it would be nice to be proved wrong since this would encourage more people to treat the floor reflection with something other than just carpeting.
Primitive root diffusers won't work well at all very close to speakers since the dispersion pattern is not finely divided enough to diffuse very well at close distances from the sound source. The
P.I. Audio Group Diffusers I use behind my listening seat have a denser pattern which works well at a three-foot distance and is of course just fine where I currently use them, behind the listening seat.
Textured foam like Sonex Classic (the wedge pattern) is super easy to attach to many ceilings. A staple gun is all that's needed to fire staples through the thin parts of the wedge pattern into drywall. That's the method I've used in my prior rooms. That doesn't work in my current room, however, since this room has all plaster walls and ceiling and the staples won't go into the plaster. Even finishing nails are not easy to pound into plaster. Instead, I use a combination of heavy duty velcro adhesive fasteners and duct tape to hold my 2' x 2' lightweight foam pieces up at ceiling height. The wall foam just leans against the wall without being fastened at all; the 4-inch flat foam is stiff and stable enough to do that even in 8-foot high stacks of two 2' x 4' panels.