DIY Room Treatment Panels - Faced or Plain fiberglass boards?

[tehas]

I'm considering building DIY room treatment panels using Knauf fiberglass panels - I believe its the same material GIK acoustics uses in their panels, and sells on their website. I'm DIY-ing because I'm on the west coast and shipping from GIK/RealTraps etc is prohibitive (basically doubles the cost).

When looking up the panels on Knauf's website, I see that they are available in FRK or ASJ facing, or plain.
For a given density, the faced panel always has a higher sound absorption coefficient in the 125 Hz octave, and lower in the highest octaves.
for example, taken from this page: https://www.knaufnorthamerica.com/e...s-insulation-board/earthwool-insulation-board
looking at 3.0 PCF (48 kg/m³) board of 2 inch thickness, the sound absorption coefficients in a Type A test (flat against a boundary, no air gap, facing outwards) are:
Plain - 0.29
FSK - 0.67
ASJ+ 0.75

I don't understand why this is, so I'm doubting these numbers. Does anyone have experience with faced vs unfaced panels and noticed or measured significantly better bass decay time improvements with the faced panels? Do you know why the faced panels are better at absorbing bass?
The other potential benefit I've noticed is that the absorption coefficients are LOWER for the faced panels at higher frequencies, which prevents the room from being too 'dead' (as recommended on Amir's review the speakers I have).
eg the 3 PCF panels at 4 kHz:
Plain: 1.03
FSK 0.28
ASJ 0.24

Basically, Is it worth spending the extra money for the faced panels?

 

[kemmler3D]

If they measure better and you trust the measurements, I'd go with it. Absorbing low is much harder than high so IMO take any performance gains you can find.

Faced might be better in that they could act sort of like membrane absorbers which would tend to do better at the low end vs. high.

But that's fairly ignorant and lazy speculation on my part...

 

[earlevel]

The short story on facing: There are specific cases of tuning for frequencies that you might want a membrane of some type, for some panels, but typically you do not want the panel faced with anything but acoustically transparent cloth.

You want the sound waves to go through the panels to the wall, the fibers absorb some of the energy (converting to heat). The overall depth from the front face to the wall determines how low the frequencies are affected. With facing, higher frequencies will bounces off, not what you want except potential for some fine tuning by someone who knows what they are doing.

 

[earlevel]

I'm considering building DIY room treatment panels using Knauf fiberglass panels - I believe its the same material GIK acoustics uses in their panels, and sells on their website. I'm DIY-ing because I'm on the west coast and shipping from GIK/RealTraps etc is prohibitive (basically doubles the cost).

When looking up the panels on Knauf's website, I see that they are available in FRK or ASJ facing, or plain.
For a given density, the faced panel always has a higher sound absorption coefficient in the 125 Hz octave, and lower in the highest octaves.
for example, taken from this page: https://www.knaufnorthamerica.com/e...s-insulation-board/earthwool-insulation-board
looking at 3.0 PCF (48 kg/m³) board of 2 inch thickness, the sound absorption coefficients in a Type A test (flat against a boundary, no air gap, facing outwards) are:
Plain - 0.29
FSK - 0.67
ASJ+ 0.75

I don't understand why this is, so I'm doubting these numbers. Does anyone have experience with faced vs unfaced panels and noticed or measured significantly better bass decay time improvements with the faced panels? Do you know why the faced panels are better at absorbing bass?
The other potential benefit I've noticed is that the absorption coefficients are LOWER for the faced panels at higher frequencies, which prevents the room from being too 'dead' (as recommended on Amir's review the speakers I have).
eg the 3 PCF panels at 4 kHz:
Plain: 1.03
FSK 0.28
ASJ 0.24

Basically, Is it worth spending the extra money for the faced panels?

I'm looking at building panels—and I've wrestled with buying from GIK or doing it myself too.

Looking at your numbers, the 4k response is what I said earlier—poor absorption for the faced panels because the highs are bouncing off. You give a reason why that might not be bad, but those panels already have mediocre low end absorption—if that's the direction you want to go, you're probably better off with bass traps.

Your "Plain" number at 125 Hz is poor (it would help to see the 250 Hz). And air gap will improve them a bit, but that's still low—4" (and a gap is possible) would be better. Otherwise, you'll be taking off highs while doing little about the lows, where problems typically lie.

I was planning on 4" panels overhead, hung from the ceiling (airgap), and 2" panels on the nearby wall, with airgap. But now I'm thinking perhaps 4" all the way. My room is not bad untreated (no parallel walls, etc.), so it seems like a good item to cut any reflections as evenly as practical across frequencies. I was planning on OC 703, but on Gearspace they say it's changed, the low end absorption is no longer adequate. Rockwool Rockboard 40 or 60, 4" is what people are recommending (if not going for really deep wall insulation/deadening), and the numbers are pretty good for 4".

 

[earlevel]

I ordered three Rockwool Rockboard 60, 4" (24" x 48") batts from Acoustimac. That will get me started with three hanging overheads in the listening / singing area, then I'll see what needs further attention. They were the best on price—highest on shipping, but still the best I could find. I'll order some Guilford of Maine fabric, lumber from Home Depot.

 

[ozzy9832001]

I just bought 4xTri Traps from GIK and they didn't do anything for my frequency response -- like not even a -1dB difference. They did however, significantly improve my decay times and made the clarity graph in REW go crazy (not sure how accurate that graph is). I'm in a smaller room (though standard home office size), 11.5x9.5x8. Still horrible standing waves at 140hz.

Not a huge deal though, the 140 peaks are EQ-able and the bass does sound significantly cleaner.

Probably need to treat a large portion of my ceiling to really dent the 140 issue, but overall it may not sure on the FR, but I can certainly hear a difference.

I had considered just putting some rockwool and wrapping it in burlap to see if that would make a difference.

Personally, if I had the time to DIY the traps I would have. I think they are all overpriced. I only went with GIK because shipped to NJ was only $60! Another company wanted $180 to ship 4 traps.

I might just order the rockwool. I have a few projects around the house that could benefit from the extra insulation if it doesn't do much.

 

[earlevel]

OK, completed, I'll try to hang them this weekend...

 

[earlevel]

And this is what they look like installed: