Unless I'm missing something in that article, I don't think it covers fluffy fiberglass, but only the 3 different densities of OC rigid fiberglass (i.e., 701, 703, 705). My understanding is that the fluffy stuff is much less dense than all of those.
The trend I see in the graphs in Ethan's article looks like this: The FRK adds LF adds more absorption when applied to 705 (as compared to 703 and 701 of equal depth), and the lowest affected frequency is lower The FRK adds LF adds less absorption when applied to 701, and the lowest affected frequency is higher and FRK on 703 rates in between the others, both in absorption amplitude, and frequency
So if this trend continues, given that fluffy FG is significantly less dense than 701, it will benefit less from FRK.
Of course, my interpretation of the graphs could be subjective, as I haven't really compared them with as much accuracy as possible. -shrug-
I disagree with your conclusions. You can see that the FRK is widening the Q of the modes, reducing decay time, and flattening the frequency response in all cases. It's hard to say exactly how much effect FRK is having with each panel thickness but it seems to work as a percentage i.e. you get more of a result with thicker panels. That's tricky though because you get a better result with thicker panels anyway. You really have to get in there with a fine toothed comb if you want to know exactly how much effect is taking place.
This isn't about density as much as it is thickness and total ft2 coverage. Fluffy behaves differently than rigid; it's not a linear relationship. We recommend a minimum of 8" thick fluffy. I haven't done any publishable tests with fluffy and FRK but, subjectively, I noticed a difference once I glued some on my super chunks.
At the end of the day, you can always tear it off.
Hmm... So the FRK trend may not carry over from rigid to fluffy.
I see clearly in the 703 and 705 tests how adding the FRK widens the Q, flattens the SPL curve, and reduces ringing. The differences between 701 and 701 FRK not much, though. 2 or 3 db flattening at best, and I don't see any difference in the ring time.
But anyway, like you say, fluffy behaves differently than rigid, so I'm not sure how much weight to give to the tests that Ethan did on rigid. I know fluffy traps should be thicker - the ceiling trap is going to be 9.25 inches of fluffy with 2.25 inches air behind it.
At this point, I'm still inclined to give more weight to the bobgolds AC page, which shows the AC of 6.5" fluffy, faced and unfaced.
I think possibly, when I said earlier in this thread, that FRK was only helpful at 250 Hz, you may have misunderstood that I was *only* talking about fluffy FG. I don't dispute that FRK improves the LF absorption with 703 and 705 - just wanna make sure that's clear.
And due to the construction method of the ceiling trap, tearing the FRK off after a month or two if I don't like it won't be a simple thing. It'd be great if I had the resources to A/B every decision point along the way, for the sake of learning about it if nothing else, but, that's not gonna happen with this room.
Hmmm... Seeing these last several posts peppered with "FRK" looks kind of like some sort of censoring is going on... WHAT THE FRK, MAN?!?!
There's definitely a reduction in ring time with the 701FRK, just not much. Look from 100Hz and up. The FRK trend is not something I've personally proven, see next paragraph, but as far as coverage and thickness translating between the two materials, I bet 5 internet points that they do.
I'm not sure what you're talking about on the Gold's page. R19 with FRK has a significantly better absorption coefficient at both 125Hz and 250Hz when flush mounted. See the section 'Owens Corning Fiberglass Batts (fluffy pink), on the wall, and 16" from the wall'. Maybe you inadvertently compared air gap to flush. Therefore, I maintain that FRK helps fluffy and rigid. You can probably get way better results using FRK and an air gap. However, you'll have to perform tests because there's no air gap data here for FRK fluffy.
You don't need to tear the FRK off 'a month or two' later. You can definitely perform a test at the time of installation. I've done similar tests to optimize my setup. You do it to not only learn but to get the most out of your investment. Had I not done so in my room, I'd be left with the wrong assumption my initial placements were best. The difference is substantial in my case and I documented the progress on this forum. I believe that log is called New Apartment, New Neighbors, New Problems. I can only advocate that you do A/B as much as you can but it's your room.
Maybe you inadvertently compared air gap to flush.
AWWWW, FRK!!!! really?! REALLY?! how'd I miss that?!
Wow, I'm glad you stuck with this thread.
Okay. We're going back to this plan: the perimeter and the rear of the ceiling shall be treated with FRK (or cardstock, or shipping paper - something close to the mass of FRK), glued to nearest face of the fluffy. Likewise with the corner chunks.
I only have these 3 internet points right now, 'cause I'm wiped out after last weekend's bender, but you can have these, and I promise I'll get the balance to you right after the 1st of the month.
FRK, FRK, FRKing FRK. I'm going back to bed. (For reals, though - I'm glad you stuck with this long enough to straighten me out.)