Skilly and Speaker Challenged I have certainly thought about how the side panels effect performance. In an ideal world I would say the AWFS pair are the tenth pair of X-LS Encores I have built and side panels did ..this…and that…and another thing. In this real world the AWFS X-LS are the first pair I have personally built and the third of forth set I have heard. Most of the others I have heard feature upgraded crossover components, that and time between auditions invalidate any listening comments I would offer with vs. without side panels.
So into the area of design intent and theory. The primary intent was to allow more than one finish to be displayed at AWFS. After the show these X-LS will be moved to domestic use. So the wilder red/blue sides can be stored away and the elegant high gloss black panels used. But of course as audiophiles and hi-fi designers we are also interested in what sound effects are. I see these as two areas. First the change in width effect on baffle step correction, second how double thick panels might change the enclosure’s contribution to the sound.
Baffle step correction (BSC) is designed into the X-LS crossover (and all other modern competent designs) adding extra bass to account for the transition from the sound radiating forward into 180 degrees to in all directions 360 degrees as the sound wavelength increase deeper into bass. The primary first order effect into the physics of BSC is the width of the baffle the woofer is mounted on. Using this (https://diyaudioprojects.com/Technical/Baffle-Step-Correction-Circuit-Calculator/
) calculator we can compare the effect of increasing the designed in 8.5 inch width with ¼”, ½”, and ¾” added side panels. The frequency F3 sited is the BSC frequency midpoint of the transition from 4π space to 2π space.
8.5 537 Hz
9.0 507 Hz
9.5 480 Hz
10 456 Hz
So Danny has designed the BSC for 530 Hz (a process for an experienced designer like him that is much more complex than the F3 number implies) then added side panels making the baffle wider move the BSC frequency down. So with an unchanged x-over wider baffles could give a bit more bass in the 450 to 540 Hz zone. Alas I lack experience to judge how immediately audible that will be. Given the choice most of us prefer a tad more bass vs less. The AWFS X-LS in my room exhibited ample strong bass.
Next is how the added thickness and mass of the side panels’ second layer change how the enclosure vibrates and radiates unwanted noise/distortion along with the desired outputs from the drivers. Given we are in GR Research’s sphere of influence start by saying the recommended attack to this issue is NoRez. No doubt it’s a more cost effective solution vs layering on extra layers of MDF or plywood. If you follow the innumerable online discussions on the topic of advanced hi-fi speaker enclosures you will have noted it typically goes something like this:
1. Poster #1 proposes using MDF or cement inches thick to brute force the enclosure spurious vibrations into compliance.
2. Poster #2 reminds the thread of the “BBC method” as in the LS3/5a when purposely light thin plywood boxes are used because they resonate at higher frequencies with Qs more easily damped with bituminous sheets (or here in GR land NoRez).
3. Poster #3 cites B&Ws matrix enclosures.
4. Posters #4 through Z cite everything from advertising fluff to peer reviewed AES papers as the thread’s signal to noise ratio approaches zero.
In the case of the AWFS X-LS with added side panels they exhibit a satisfying heft, our scale reported this to be 24.4 pounds for a fully loaded speaker. Presently there is no damping between the enclosure side walls and added side panels. Deadline and the priority to allow easy changing of panels for the show took priority over tweaking. When time allows I would try first felt between layers for damping that still allows easier panel swaps. If the side panels are to be permanently attached next step is to look into lossy adhesives that will convert the enclosure side walls and side panels into a constrained layer damping system. That is of course a deep rabbit hole to dive into that can vary from trying the first thing found at the hardware store up to experiments documented with accelerometers on the enclosure.
Regarding the tweeter cover’s effect on response that is something Danny could measure, I have some wave guides cooking and when those go to him I will send an example for him to test.