Glad to help
Originally Posted by popalock
IF (and it's a big if) I am able to get the LCR I am gunning for, I might end up making a few more updates that could effectively eliminate the need for treatments behind my screen all together.
I understand, work in progress ....
The only way to eliminate the need for acoustic treatment up on the front boundary of the room is to implement a baffle wall. A baffle wall has many theoretical advantages to any other loudspeaker placement approach. However, unfortunately a baffle wall also heightens the importance of rear wall treatment because all front sources are placed at the pressure maximum. If all the pressure sources are located in the same plane and at the pressure maximum, all modal resonances front-to-back are maximally excited. Hence the concern for rear wall damping.
Studios employ flush mounted mains for a very simple reason; optimal wave-launch. First the boost gained from all the energy that otherwise would radiate omni-directionally is focused forward and not smeared in time from the bounce off the surface behind the speakers. So increased image focus, and significant smoothing to the frequency response. Also any slight disturbances or very early reflections or re-radiations (diffraction) of the wave-launch are lessened. Again smoothing the FR and retaining the wave-launch as un-corrupted as possible.
Originally Posted by popalock
I still have quite a ways to go in order to get a firm grasp on SIBR, but my preliminary research indicates that the preverbal "wall of sound" would effectively eliminate the need for treatments behind the screen, correct?
Not necessarily. Even if you employed the Noesis LCRs, and some other sub cabs, etc, you could still benefit from LF damping, modal damping of the front-to-back axial modes. This helps in both FR smoothing and lowering LF decay times.
In battling room modes in small rooms, in any of the three axis with absorption type treatment, one needs to use one boundary or the other, or ideally both. That said, if you went with your wall of sound, you could still benefit from a bunch of fluffy/rigid up higher etc., or wherever you could place it. Also, be mindful, many surface irregularities up front, could be detrimental to the image throw. Yes, constant directivity or any measure of directivity helps remove some of these issues, but just be mindful of several cabs up front somewhat incongruously set up.
I know, splitting hairs, .. ate up, anal retentive, just throwing items out there. Please don't misunderstand, merely trying to help. Poorly executed front of the room speaker set up is so pervasive around here. I see so many fantastically time consuming builds, yet it's easy to disregard some crucial fundamentals. If that initial wave launch is corrupted, being thrown at you smeared from multiple path lengths, the image detail, vocal intelligibility, and all the smaller nuances that the engineers tried so hard to capture, no amount of treatment, EQ, DSP can make up for it.
We love our big bombastic bass effects that accompany out favorite material. But our hearing acuity is most sensitive to the critical mid-band. Examining and addressing any potential issues in the mid-band is a force multiplier for our systems akin to nothing else we can do. Fortunately, psychoacoustics allows us to "hear past" many of the common issues we encounter. But any attempts lessening these acoustic distortions pays off huge in subjective contexts like smoothness, ease, image coherence, detail.
I know many hate such terminology, but subjectively we do attempt to describe the changes to the playback experience, as we move forward addressing the lowest hanging fruit we encounter.
Anyway, this turned into a mega response, my apologies. After the launch and direct sound, the remaining elements of the room's acoustic comes into play. That's an entire discussion into itself. But the most important component is bass trapping. Reducing the LF decay times, monumentally important, as increased clarity and detail, note-to-note delineation. As much effective bass trapping as you can aesthetically stand.
Regarding your sub system, .. from the first time I saw this group of (16)18"s, and knowing what all I discovered wrt multi-sub optimizing, I envisioned an opportunity for time delay attenuation of whatever modal issues arise front-to-back.
A variety of acoustic components at play;
It would appear the height and width modes are dealt with adequately via spreading of the sources as you have them, .. so we'll examine what could be done elsewhere, ie front-to-back.
1.) The seating is so close to the rear boundary, the listener is in a high pressure region (peaky response). Typically in this situation, you apply as much absorption thickness as possible behind the LP.
2.) It's not often achieved in practice, but ideally
, one wants as many dedicated amp channels and corresponding DSP channels to provide differing amounts of time delay to manipulate acoustic summation of all the disparate sources. Individual EQ isn't an absolute necessity (individual low pass can help), global EQ (all the subs as one) is generally fine to tune the final response. But having the ability to tune via time delay specific groups of LF sources really is a powerful tool.
3.) In your system, the listener is (relatively speaking in 1/4 wavelengths) very close to some of the drivers, and significantly farther to other groups of drivers. If you could optimize the way the rear drivers sum at the listening position (time delay), and then take that group and align them with the front sub towers, I'd bet you could elicit even more smoothness in the freq domain.
4.) A final step is global EQ, knocking down whatever peaky response issues remain. Nulls are typically acoustic interference, peaks are typically modal excitation. As I mentioned above, if you have the ability to vary each groups low pass (the upper roll off), that too is a good tool to manipulate the FR smoothing. Any way you can manipulate the way the drivers sum is another arrow in your quiver.
Yeah, this post got away from me a bit. You may find the existing FR not too bad. That doesn't mean the subs are all playing nicely. The path lengths are all so dramatically different, and that's the genesis of the point I was trying to make. As good as it is right now, I'm thinking there's a lot left on the table.
Hope this helps,
All the bestHere's
Genelec's take on some aspects of what I was discussing.