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Could someone help out interpreting material's gas flow properties Bass Traps
Old 18th March 2008
  #31
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Quote:
Originally Posted by Ydope View Post
BTW where do these values for 703 and 705 come from? I found no orignal data. If 703 has 16 kPa it seems likely that 705 has at least twice that value, because that's what I found with comparable materials.
Your question piqued my interest. I recall the values for 703 in an academic paper on the web, but have not been able to find it. I sent an email to OC asking for GFR data on 701, 703, and 705.

In the interim I had look at NRC IR 761 for the physical properties of the insulation they used in their tests. The closest materials to what we are talking about are:

"Mineral Fibre (M2)", average density 44.2 kg/m^3 GFR 16,000 mks rayls/m; and
"Mineral Fibre (M3)", average density 98.1 kg/m^3 GFR 58,000 mks rayls/m.

The first (very roughly) equivalent to 703, and the latter to 708. I would have though the same as you wrote, that the relationship between density and GFR would be roughly linear. However would imply a GFR of around 40,000 mks rayls/m for 708.

BBC uses 6,000 mks rayls/m as the value for RW2 Rockwool in its RD reports.

Bradford in Australia is one of the few (if not only) companies that publishes GFR data. Bob Gold has included it in his page.

I hope this helps a bit.

Flowingly,
Andre
Old 18th March 2008
  #32
Gear interested
 

Andre,

appreciate the info, hope they come back at you.
Isn't that M3 product quite close to OC 705? 705 has also got about 90-100 kg/m³

Here are GFRs (in kPa*s²/m²) for German products I could come up with. You can see the density by looking at the name. DP-3 has about 30 kg/m³ for example.

"Heraklith Heralan" Rockwool:
DP-3: > 5
DP-4: ≥ 7
DP-5: > 7
DP-7: > 7
Dp-10: ≥ 20
DP-12: ≥ 25
DP-15: ≥ 25
(Knauf Insulation)


"Rockwool" rockwool:
Termarock 30: > 9
Termarock 40: > 12
Termarock 50: > 15
Termarock 100: > 43
(Baushop.DE: 350.857 günstige Artikel, News auf Bau online - baustoffmarkt-online)


"Isover" Rockwool:
SP 120: ≥ 40
SP 150: ≥ 50
SP 180: ≥ 70


"HOMATHERM flexCL", made from cellulose, which has also good absorption coefficients:

about 70 kg/m³: 43 - 76
(Saint-Gobain Isover G+H AG - mit dem Scout zum richtigen Dämmstoff)


Greets,
Jules
Old 18th March 2008
  #33
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Quote:
Originally Posted by Ydope View Post
Isn't that M3 product quite close to OC 705? 705 has also got about 90-100 kg/m³
I checked the 705 specifications and you are correct. 705 has a nominal density of 96
kg/m^3.

Quote:
Here are GFRs (in kPa*s²/m²) for German products I could come up with
.

Thanks for the information. Unfortunately all that that showed up in the post was the names and densities. No GFRs.

I had tried to send emails to several other Canadian makers of insulation to get their GFR data but all but one had changed their URLS and I could not even get results searching for them. The one company that I was successful with was Roxul.

So hopefully we have a set of GFR data from one glass mineral fibre maker (Owens Corning), and one mineral wool maker (Roxul). Roxul uses slag, the floating material from blast furnaces for making steel, as its fibre source.

Andre
Old 19th March 2008
  #34
NLP
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Old 19th March 2008
  #35
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Quote:
Originally Posted by NLP View Post
Food for brains:
ready trap bags: sag?
my post...
What is the point of your link? You have already written in this thread that you do not believe in the physics involved. If you think there is something magical about corners, read post #28 carefully and absorb it. What happens completely in a corner is not completely understood. But there is no great mystery to it.

Politely,
Andre
Old 19th March 2008
  #36
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Quote:
Originally Posted by avare View Post
Thanks for the information. Unfortunately all that that showed up in the post was the names and densities. No GFRs.
No, theres the product name, a colon and the GFR in (in kPa*s²/m²)

For example "DP-3: > 5" means that the product called DP-3 (which has about 30 kg/m³) has more than 5 kPa*s²/m² according to it's technical data.

I was too lazy to include the unit every time.
Old 19th March 2008
  #37
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Quote:
Originally Posted by Ydope View Post
No, theres the product name, a colon and the GFR in (in kPa*s²/m²)

For example "DP-3: > 5" means that the product called DP-3 (which has about 30 kg/m³) has more than 5 kPa*s²/m² according to it's technical data.

I was too lazy to include the unit every time.
Thank you!

Andre
Old 19th March 2008
  #38
NLP
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Quote:
Originally Posted by avare View Post
What is the point of your link? You have already written in this thread that you do not believe in the physics involved. If you think there is something magical about corners, read post #28 carefully and absorb it. What happens completely in a corner is not completely understood. But there is no great mystery to it.

Politely,
Andre

Yes there is no mistery! What corners? Read just my post. But like I said, different! additions in different! proportions are added in every! specific product. I know that, because I do that. The insulation is not made just from wool... and in technological processs of making acoustic! insulation is few more factors. But this are the small "secrets" (not magic) of each company.
Old 19th March 2008
  #39
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Roxul GFR Response

I received a reply from Roxul re: GFR for their materials. The only material that they had data for was AFB. AFB is 2.8 pcf and has airflow resistivity at 3" of 16,600 mks rayls/m and for 1.5" 15,000 mks rayls/m.

Andre
Old 31st March 2008
  #40
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Quote:
Originally Posted by avare View Post
I received a reply from Roxul re: GFR for their materials.
Nothing from OC so far?
Old 2nd April 2008
  #41
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Quote:
Originally Posted by Ydope View Post
Nothing from OC so far?
My computer was down for several days. OC responded with the following data:

701 8,300
703 16,00
705 30,00

Andre
Old 28th May 2008
  #42
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Quote:
Originally Posted by esaias View Post
in other words, what does this mean and how does it relate to acoustical/absortion properties (and compared to for example ever so popular OC703). For example here is airflow resistivity properties of PAROC COS 5
( Pääsivu )

45 10^-6 m^2/sPa

http://www.paroc.com/spps/BI_attachm...ance_table.pdf

What does these figures actually mean?


This material was named by Paroc representative when I asked about rigid wool/fiber slabs which had density around 40-50 kg / m^2 although the guy could not give any ideas how the material works in acoustical sense.

I'm just looking for cheaper options than real acoustic rigid wool/fiber which is very expensive. I was thinking of putting these inside larger panels and use real acoustic (3,5cm think with fibreglass cloth) slabs, which I already have, as surfaces.

Thank you,

-Tomi H
So... Did you buy something???
What's the solution for acoustical treatments in FINLAND???

Can it be this difficult, PERKELE!
Old 3rd September 2008
  #43
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Quote:
Originally Posted by avare View Post
My computer was down for several days. OC responded with the following data:

701 8,300
703 16,00
705 30,00

Andre

Hi Andre,

I´m looking for something simmilar to OC 703 (which is not available in Germay) so I´m wondering, what is the unit of measurement of your above posted 16,00? Is it kPa*s/m²?

Thanks and have a nice day!
Old 3rd September 2008
  #44
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Quote:
Originally Posted by freequency View Post
Hi Andre,

I´m looking for something simmilar to OC 703 (which is not available in Germay) so I´m wondering, what is the unit of measurement of your above posted 16,00? Is it kPa*s/m²?

Thanks and have a nice day!
It is mks Rayls. Without double checking it. The easiest thing to look for is mineral wool with a density around 64kg/m^3. If you are building absorbers thicker than 150 mm, look for lighter material.

When you find something, a link a would be appreciated.

Andre

Last edited by avare; 6th September 2008 at 04:12 AM.. Reason: Corrected units, and then corrected incorrect correction
Old 8th September 2008
  #45
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Quote:
Originally Posted by avare View Post
When you find something, a link a would be appreciated.

Andre
I think Termarock 50 is realy close to OC 703 and available in Germany. It´s 50 kg/m³ and about 16 kPa * s/m² (as Ydope already posted).

http://www1.rockwool.de/graphics/Tes...ten_150306.pdf

Thanks!
Old 10th March 2009
  #46
zkn
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I probably summon forth old demons here but after reading through this thread over and over again, I still cannot figure out that Paroc table in the initiator's first post of this topic..

Maybe I'm plain stupid or didn't pay enough attention in high school physics and math classes, but on Paroc website they have an equation which can be used to calculate the air flow resistance: AF = d/A*l

So for instance:
Thickness, d (mm) = 10
Air Permeability, l (m2/Pa s 10-6) = 5
now, having put those numbers in the formula, I get AF = 2 which is also presented in the table under Rs column.

But Airflow Resistivity, r (kPa s / m2) for the same numbers is 200

As I understand, this is the most important figure to look at when it comes to choosing a suitable wool / fiber for an absorption application, but how do I get that using the above formula and data?
Old 10th March 2009
  #47
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Like the air permeability and material thickness values on that page, the flow resistivity values are given. They can't be determined using that table. They have to be measured in a lab.
Old 10th March 2009
  #48
zkn
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Quote:
Originally Posted by Brainchild View Post
Like the air permeability and material thickness values on that page, the flow resistivity values are given. They can't be determined using that table. They have to be measured in a lab.
Some wool / fiber producers show only Air Permeability and no Airflow Resistance info, however isn't there a correlation between the two, meaning the higher the permeability, the lower the resistance, for example? or not?
Old 10th March 2009
  #49
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Oh, right, I see. So, if you know the permeability, then, yeah, the flow resistivity is just 1/permeability (and then multiply by 1,000 to get the same units they're using in that table).
Old 11th March 2009
  #50
zkn
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Quote:
Originally Posted by Brainchild View Post
Oh, right, I see. So, if you know the permeability, then, yeah, the flow resistivity is just 1/permeability (and then multiply by 1,000 to get the same units they're using in that table).
Ok, and if the units are presented in kPa then for example in Porous Absorber Calculator where it needs rayls/m I need to multiply by 1000 again, yes?
Old 11th March 2009
  #51
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Yes.
Old 12th March 2009
  #52
zkn
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Let's see if I interpret the table correctly using the help of a Porous Absorber Calculator.

Say, I need to achieve the following result in a below graph.

The absorber is 40mm thick with a 700mm air gap behind it.

Now am I deriving the figures correctly that in order to get such absorption results, I need to choose a wool with Rs value "8" to get 8000 rayls/m which is a material with a uniform Airflow Resistivity value of 200 kPa s/m2 (in the first column) ?

Thanks to everyone for bearing with me, I just want to get my head around this thing for once and for all.
Attached Thumbnails
Could someone help out interpreting material's gas flow properties-graph.jpg  
Old 12th March 2009
  #53
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Actually, ralys/m is the flow resistivity value. So, 200 kPa s/m2 = 200,000 rayls/m. It would be like putting 200,000 in the field in the absorber calculator where you have 8,000.

In the case you used, the flow resistivity is 8,000 rayls/m [8 kPa s/m2]. So, for 40mm of material, the specific absorption is about 320 rayls.

So, in this case, you would want a material with an Rs value of 320 rayls for 40mm thickness. That number would only apply to the specific thickness of that particular product.
Old 12th March 2009
  #54
zkn
Gear interested
 

Quote:
Originally Posted by Brainchild View Post
Actually, ralys/m is the flow resistivity value. So, 200 kPa s/m2 = 200,000 rayls/m. It would be like putting 200,000 in the field in the absorber calculator where you have 8,000.

In the case you used, the flow resistivity is 8,000 rayls/m [8 kPa s/m2]. So, for 40mm of material, the specific absorption is about 320 rayls.

So, in this case, you would want a material with an Rs value of 320 rayls for 40mm thickness. That number would only apply to the specific thickness of that particular product.
Hence, if according to the PACalc I get the best result for a 40mm thick absorber at 14,000rayls/m, I just need to find a wool/fiber that has 14kPa s/m2 of flow resistivity, and that it?
Old 12th March 2009
  #55
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Yup!
Old 12th March 2009
  #56
zkn
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I've made some research and for what it's worth, here's an overview of some mineral wool products that should be commonly available in most countries in Europe and to my knowledge can be used as OC substitutes.

PAROC: COS 5
Type: semi-rigid
AFR, Pa: 22 222
WxL, mm: 600x1200 (alt. 600x1500)
Thickness, mm: 30-140 (100-180)
Density: 60-80 kg/m3

PAROC: COS 10
Type: rigid
AFR, Pa: 28 571
WxL, mm: 600x1200
Thickness, mm: 30-180
Density: 100 kg/m3

PAROC: COS 15

Type: rigid
AFR, Pa: 66 667
WxL, mm: 600x1200
Thickness, mm: 30, 50, 100, 120, 140, 160
Density: -

PAROC: FPS 14
Type: rigid
AFR, Pa: 20 000
WxL, mm: 600x1200
Thickness, mm: 20-120
Density: -

PAROC: UNS 37
Type: flexible
AFR, Pa: 7 629
WxL, mm: 565x1320 (alt. 870x920; 610x1170; 260x1320)
Thickness, mm: 30-200 (100 - 175; 50 - 175; 50)
Density: 26 kg/m3

PAROC: UNS 35
Type: flexible
AFR, Pa: 9 091
WxL, mm: 565x1320 (alt. 870x920; 610x1170)
Thickness, mm: 30-175 (100 - 200; 50 - 175)
Density: -



ROCKWOOL: Multirock 35
Type: semi-rigid
AFR, Pa: 10 000
WxL, mm: 1000x565 (alt. 1000x610)
Thickness, mm: 50, 75, 100, 120, 150, 200 (50, 75, 100, 120, 150, 200)
Density: 35 kg/m3

ROCKWOOL: Rockton
Type: semi-rigid
AFR, Pa: 16 667
WxL, mm: 1000x600
Thickness, mm: 50, 80, 100, 120, 150
Density: 50 kg/m3

ROCKWOOL: Fasrock
Type: rigid
AFR, Pa: 33 333
WxL, mm: 1000x500
Thickness, mm: 20, 30, 50, 70
Density: 135 kg/m3


ROCKWOOL: Industrial Batts Black
Type: rigid
AFR, Pa: 14 286
WxL, mm: 600x1200
Thickness, mm: 15, 20, 30, 50
Density: 60 kg/m3


As you can see, some of the above are more similar to OC-703/705 some are less, but nevertheless I think all of them have use in some situations.

with kind regards.
Old 16th November 2009
  #57
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Quote:
Originally Posted by Hannes_F View Post
Hi Andre,

sorry, maybe I did not get what you mean.

I am using material with low flow resistivity, around 5000 Pa*s/m². Cheap stuff.

Test these values in the Porous Absorption calculator:

Absorber thickness 100 mm
Air gap 100 mm
Start graph at 30 Hz.
Absorber flow resistivity 5000 or 16800 or 45000 Pa*s/m².



First, we see that the absorption is definetely different in the bass range.

Then, if we compare the 5000 Pa*s/m² with the 16800 Pa*s/m² curve we see that below ca. 135 Hz the absorption is better for the the more resitive material. Tests have shown this as well like Ethan Winer's site shows.

However if this leads to a "more is always better" thinking this could be an error. If you watch the curves closely you will see that there is a frequency range between 135 and 700 Hz where the fluffy 5000 Pa*s/m² material absorbs better. Moreover, the 45000 Pa*s/m² material aborbs worse than the 16800 Pa*s/m² material.

This is definetively counter intuitive. But if you think about it then denser material should be good for insulation, and this can include a good portion of backscattered energy.

Now enter an absorption width of 300 mm and a gap of 200 mm. Surprise - the 5000 Pa*s/m² is best!



If this is true then my conclusions are:

- If you are restricted to panels in the range of 10 cm or 4 " then material in the range of 16000 - 25000 Pa*s/m² is probably your best choice. With other words OC 703 or 705. (But do yourself a favor and don't ignore the demand for an air gap behind them).

- If you have more space then consider thicker absorbers with bigger gaps, filled with fluffy glass wool of 5000 Pa*s/m² or even less.

Now how relevant are those simulated values?

#1 Download the software ZORBA by Marshall Day Acoustics for a double check. It says the same if you activate "alpha normal". If you check their website you see that they verified their simulations with experimental data and the two are very close.

# 2 I am not finished yet with my studio but the traps that I installed so far behave exactly as they should according to these simulations.

My conclusions:
- More is not always better.
- It always depends (i. e. on the frequency range, the absorber width and position, the gap width)
- I try to know what I am doing. Read, read, read (I mean books, scientific articles, papers - not necessarily forum opinions).The links to the literature are everywhere. Start at the bottom of this site: http://www.bobgolds.com/AbsorptionCoefficients.htm . Read all the BBC articles about their acoustics tests.
- I try to understand the theory but also run tests in between.

Somebody who does not know what he/she is really doing may end up spending much money with mediocre results. Cruel but true :-)

Hope this helps
Hannes
Could you let me know exactly what is the 5000 Pa*s/m² material?

i meant product name ,model name or brand name etc..
thank u..
Old 16th November 2009
  #58
Victor_Stoian
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Old 18th January 2010
  #59
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so...without getting technical..can someone explain what this all means?

less dense with an air gap is superior in absorbing low frequencies compared to more dense with/without air gap
Old 18th January 2010
  #60
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Quote:
Originally Posted by takman View Post
so...without getting technical..can someone explain what this all means?

less dense with an air gap is superior in absorbing low frequencies compared to more dense with/without air gap
You have left out the material thickness. heh
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