John Sayers' Recording Studio Design Forum Archive

I am (finally) at the drywall installation portion of my studio build, and I've ended up with a lot of extra pink fluffy (low density fiberglass) insulation. Is there any use for this in acoustic treatment? I was planning on building all of my absorption panels, bass traps and clouds... so if I could simply use all of this left over insulation, that would make me and my wallet (and therefore my wife) incredibly happy. But most of the DIY panels I've seen have either been mineral wool or 703/705.

If not, I can probably sell the leftovers, or maybe even return them. But in the interest of saving time and money, I'd like to use them if I can.

Jag94 wrote:I am (finally) at the drywall installation portion of my studio build, and I've ended up with a lot of extra pink fluffy (low density fiberglass) insulation. Is there any use for this in acoustic treatment? I was planning on building all of my absorption panels, bass traps and clouds... so if I could simply use all of this left over insulation, that would make me and my wallet (and therefore my wife) incredibly happy. But most of the DIY panels I've seen have either been mineral wool or 703/705.

If not, I can probably sell the leftovers, or maybe even return them. But in the interest of saving time and money, I'd like to use them if I can.

Yes, it is perfect for bass traps and first reflection points.

There is really no need to use denser insulation for most treatments, and many use it due to believing that denser is better for low frequency absorption, but at thicknesses over 4" the opposite is true. And even a 4" panel from dense insulation will not be very effective below 500hz.

A handy tip is to cover the pink fluffy in a layer of polyester wadding (Dacron) before covering in fabric, since it will stop fibres from escaping (if you're worried about that) and provide a nicer, upholstered finish if done correctly.

Paul

Yes, it is perfect for bass traps and first reflection points.

There is really no need to use denser insulation for most treatments, and many use it due to believing that denser is better for low frequency absorption, but at thicknesses over 4" the opposite is true. And even a 4" panel from dense insulation will not be very effective below 500hz.

A handy tip is to cover the pink fluffy in a layer of polyester wadding (Dacron) before covering in fabric, since it will stop fibres from escaping (if you're worried about that) and provide a nicer, upholstered finish if done correctly.

Paul

Hi Paul, thanks for chiming in (as usual!). Are you saying that using rockwool and owens corning 703/705 offer no benefits over regular fluffy fiberglass insulation? It seems like 99% of panels that I've seen people DIYing, and also panels that you can purchase all either have rockwool or 703/705, even though both are more expensive than the fluffy fiberglass stuff.

I am afraid I have to disagree Paul. 100mm OC703/5 with 48/96 KG densities both have 85% Absorption in the 125Hz Octave Band.
On top of this, semi rigid panels have a damped membrane behaviour, which is most notable in corners. IMO such designs punch way above their weight.

Of course much thicker traps which require much lighter cheaper fibre are better.

DanDan wrote:I am afraid I have to disagree Paul. 100mm OC703/5 with 48/96 KG densities both have 85% Absorption in the 125Hz Octave Band.
On top of this, semi rigid panels have a damped membrane behaviour, which is most notable in corners. IMO such designs punch way above their weight.

Of course much thicker traps which require much lighter cheaper fibre are better.

Hi Dan, I respect your knowledge and experience, I believe you because you've said it, however I'd be interested to see data showing a 85% @ 125hz, I've read about this but never seen anything backing it up. What is the GFR of OC705? I have always believed it to be 30k rayls.

This is what I get when I input 100mm w/30000GFR
Paul

And with the Komatsu porous model: Paul

DanDan wrote:I am afraid I have to disagree Paul. 100mm OC703/5 with 48/96 KG densities both have 85% Absorption in the 125Hz Octave Band.

Dan, these are outdated numbers. OC 700 formula was either changed few years ago, or they re-tested 700 series with much worse outcome.
The most recent official OC test measurements are:
Hz........................................................... 125. 250. 500 1000 2000 4000 NRC
703, plain 4" (102mm) on wall 3.0 pcf (48 kg/m3): 0.51 1.19 1.24 1.13 1.04 0.94 1.15
705, plain 4" (102mm) on wall 6.0 pcf (96 kg/m3): 0.60 1.16 1.15 1.09 1.10 1.06 1.15
https://www.owenscorning.com/dms/10021736

Thermafiber made by OC now has better specs:
Thermafiber SAFB 4" 2.5 pcf: 0.83 1.19 1.27 1.12 1.12 1.13 1.20
Thermafiber SAFB 6" 2.5 pcf 1.37 1.32 1.23 1.16 1.12 1.12 1.20

https://www.owenscorning.com/dms/10021143
https://www.owenscorning.com/dms/10022322

And the same (better absorbtion specs than 703/705 at 125 Hz) is true for Knauf Earthwool, Rockboard, and Johns Manville 1200 series:

Knauf Earthwool 4" (102mm) 3.0 PCF (48 kg/m³) 0.95 1.11 1.17 1.07 1.07 1.06 1.10

Rockboard
RXL 40 4" (100mm) 4.0 pcf (64 kg/m3) 1.03 1.07 1.12 1.04 1.07 1.08 1.10
RHT 40 4" (100mm) 3.5 pcf (56 kg/m3) 1.07 1.01 1.07 1.06 1.07 1.16 1.05
RHT 60 4" (100mm) 4.4 pcf (70 kg/m3) 0.92 1.04 1.07 1.07 1.07 1.08 1.05
RHF / RHT 80 4" (100mm) 5.9 pcf (94 kg/m3) 1.00 0.95 1.06 1.04 1.06 1.08 1.05

Johns Manville
1240 4" (100mm) 4.0 pcf (64 kg/m3) 0.88 1.14 1.17 1.08 1.06 1.10 1.10
1240 6" (150mm) 4.0 pcf (64 kg/m3) 1.32 1.14 1.11 1.09 1.06 1.07 1.10
1260 4" (100mm) 6.0 pcf (96 kg/m3) 0.99 1.01 1.10 1.03 1.03 1.05 1.05
1280 4" (100mm) 8.0 pcf (128 kg/m3) 1.11 0.91 1.03 1.06 1.06 1.07 1.00

I don't know how OC managed to do this, but OC 703/705 is not a recommended option for acoustic treatment anymore.

OC703 has Mythological status, probably because of Everest books etc. It has been called 'the ideal absorber'
Weirdly I have never seen it. It does not seem to be distributed well.
There have been other anomalies, very varied GFR figures. So it has almost certainly varied in composition over the years.
I note in the new data that Thermafiber (2.5pcf) which is close to the 3pcf of 703 has an alpha of 0.83. Same old?

So overall I am quite pleased to see those updated data, thanks kosulin. They show many 100mm batts with great absorption in the 100Hz region.
Now I am much more confident recommending Caruso Isobond and other Polyesters, which have seemingly quite good absorption, although nothing like some of the best here.
Paul, bobgolds.com has been the go to for yonks.
Also, if you play with angles in that modelling software you can get better and worse predictions.
Here's 703, 100mm 75 degrees However, there is no facility for predicting how a batt of 705 straddling a corner will perform. I believe the corner magnification coupled with a damped resonant effect is very powerful.
There are lab tests which show it at studiotips. Note in particular the comparison of the very large 32" wide StudioTips Superchunks, same width MegaLenrds, and the only 24" wide 703 straddling the corners. The latter is remarkably close to the big boys. I believe the damped membrane effect is even stronger with 705, which definitely resonates when you thump a suspended panel. (MiniTrap)

Jag94 wrote:I am (finally) at the drywall installation portion of my studio build, and I've ended up with a lot of extra pink fluffy (low density fiberglass) insulation. Is there any use for this in acoustic treatment? I was planning on building all of my absorption panels, bass traps and clouds... so if I could simply use all of this left over insulation, that would make me and my wallet (and therefore my wife) incredibly happy. But most of the DIY panels I've seen have either been mineral wool or 703/705.

If not, I can probably sell the leftovers, or maybe even return them. But in the interest of saving time and money, I'd like to use them if I can.

For what it is worth, Carl Tatz says only use 703 or 705 (foil faced) saying tha fluffy is not good enough, rigid has more density.

mlbchitown wrote:

Jag94 wrote:I am (finally) at the drywall installation portion of my studio build, and I've ended up with a lot of extra pink fluffy (low density fiberglass) insulation. Is there any use for this in acoustic treatment? I was planning on building all of my absorption panels, bass traps and clouds... so if I could simply use all of this left over insulation, that would make me and my wallet (and therefore my wife) incredibly happy. But most of the DIY panels I've seen have either been mineral wool or 703/705.

If not, I can probably sell the leftovers, or maybe even return them. But in the interest of saving time and money, I'd like to use them if I can.

For what it is worth, Carl Tatz says only use 703 or 705 (foil faced) saying tha fluffy is not good enough, rigid has more density.

More density = more reflective

Higher density causes more interference with the waves. This takes the form of absorption and a tiny amount of reflection.
At the edge of the hyperbolic envelope of course fully density non fibrous glass and basalt reverse behaviour and are entirely reflective.

Vice versa one could say that lighter fibre is more absorptive. Taken again to hyper extent, clearly no fibre would be the best absorber.

Let's be reasonable. 100KG or thereabouts is the best choice for the common 100mm trap for both absorption and construction reasons.
Other fibres are becoming available that function well at only 40KG.

100mm of light fluffy insulation would be difficult to frame, to contain, and would have very poor absorption at lower frequencies.
But, it is the best choice in partitions where the containment is a given, and denser materials have not performed any better or even differently in tests.