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Broadband absorbers with Homatherm FlexCL - how thick? Studio Headphones
Old 12th September 2018
  #1
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Broadband absorbers with Homatherm FlexCL - how thick?

Hi there,

I am planning to built some broadband-absorbers myself.
Right now I am using 10cm Basotect at the first reflection points but I feel I can do better with Homatherm!
Since Homatherm FlexCL has an extremely high flow resistance, it's not so suitable for building basstraps. So therefore I will use Rockwool/Sonorock in the corners.

However Homa FlexCL looks perfect for first reflection absorbers for the walls and ceiling.
What I am not sure about, is how thick those absorbers should be?!
Is 10cm Homatherm FlexCL good enough?
I read somewhere that FLexCL should not be used too thick, because it will then start to reflect again.

Maybe someone can shed some light in the dark
That would be highly appreciated

Last edited by Northward; 18th September 2018 at 10:07 AM..
Old 12th September 2018
  #2
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Homatherm decided a couple weeks ago to stop all production. These products are not available anymore...

We're looking for replacements.
Old 12th September 2018
  #3
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Quote:
Originally Posted by Northward View Post
Homatherm decided a couple weeks ago to stop all production. These products are not available anymore...

We're looking for replacements.
Holy Crap!? WHAT..??
Didn't see that comming

Wonder why they withdraw.. you seem to been their best customer haha.
So their sales couldn't be that bad.

Thanks for the heads-up, Thomas
Old 14th September 2018
  #4
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Quote:
Originally Posted by midmost View Post
Holy Crap!? WHAT..??
Didn't see that comming

Wonder why they withdraw.. you seem to been their best customer haha.
So their sales couldn't be that bad.

Thanks for the heads-up, Thomas
Myself and others anyway don‘t understand
why using that FlexCl stuff for bass traps as its
air flow resistance is so high.
HolzFlex is better. I used instead of HolzFlex SteicoFlex because HolzFlex was not abailable anmore. it has 5kpa.
Old 14th September 2018
  #5
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Quote:
Originally Posted by ak23 View Post
Myself and others anyway don‘t understand
why using that FlexCl stuff for bass traps as its
air flow resistance is so high.
HolzFlex is better. I used instead of HolzFlex SteicoFlex because HolzFlex was not abailable anmore. it has 5kpa.
That's because in our case Flex CL wasn't used primarily for its flow resistance but for its mechanical properties when mounted within a certain sequence. Holzflex has too big fibers to be a good flow based absorber.
Old 14th September 2018
  #6
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Quote:
Originally Posted by ak23 View Post
Myself and others anyway don‘t understand
why using that FlexCl stuff for bass traps as its
air flow resistance is so high.
HolzFlex is better. I used instead of HolzFlex SteicoFlex because HolzFlex was not abailable anmore. it has 5kpa.
No one said I was going to make bass traps from it
Old 17th September 2018
  #7
Gear Nut
 

Quote:
Originally Posted by Northward View Post
That's because in our case Flex CL wasn't used primarily for its flow resistance but for its mechanical properties when mounted within a certain sequence. Holzflex has too big fibers to be a good flow based absorber.
Yeah and Holzflex has also 5kpa as most other Rockwool products right ?
But 5kpa are 5kpa even if the fibers are too big! In the high/mid frequency range it reflects more but bass should be the same i guess.
Old 18th September 2018
  #8
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Quote:
Originally Posted by ak23 View Post
Yeah and Holzflex has also 5kpa as most other Rockwool products right ?
But 5kpa are 5kpa even if the fibers are too big! In the high/mid frequency range it reflects more but bass should be the same i guess.
Fibers size affects the absorption coefficient substantially. For a similar resistance to flow and density, there is an increase in absorption coefficient alongside a decrease in fibers diameter.

This is mainly due to thinner fibers being able to move more easily compared to thicker fibers. Thinner fibers structures also have a more tortuous path which means increased friction and viscosity.

This factor is called "Tortuosity" and is a "measure of the elongation of the passage way through the pores", basically the influence of the complex internal structure of a material on its acoustical properties.

Generally speaking, tortuosity affects the location of the 1/4th wavelength absorption peak, while porosity and resistance to flow affect the height and Q of the peaks.

Looking at the resistance to flow value and density is a good hint at what a material's properties are likely to be, but it's not the whole picture, so it must be put in perspective alongside other factors and materials properties - that are not always available which is a problem.

While Holzflex is a good thermal product and a welcomed green alternative, it is not a very good absorber due to its mechanical properties. Especially in the LF.
Old 18th September 2018
  #9
vdH
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isover ultimate

Quote:
Originally Posted by Northward View Post
Homatherm decided a couple weeks ago to stop all production. These products are not available anymore...

We're looking for replacements.
Have you considerd Isover Ultimate?

http://www.isover-technische-isolati...9c598fe39b.pdf

It looks promising....
Attached Thumbnails
Broadband absorbers with Homatherm FlexCL - how thick?-screen-shot-2018-09-18-22.01.29.png  
Old 18th September 2018
  #10
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Quote:
Originally Posted by vdH View Post
Have you considerd Isover Ultimate?

http://www.isover-technische-isolati...9c598fe39b.pdf

It looks promising....
What a great document! Pdf page 19 gives the GFR by product.

Thank you!

Andre
Old 19th September 2018
  #11
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Does it make any sense to make superchunks (corner absorbers) from Homa Flex CL?
Old 19th September 2018
  #12
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Quote:
Originally Posted by midmost View Post
Does it make any sense to make superchunks (corner absorbers) from Homa Flex CL?
Not really no.
Old 19th September 2018
  #13
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Quote:
Originally Posted by Northward View Post
Not really no.

Okay, you'll find me getting a bit frustrated at this point ;(
I have 5 packages of Flex CL (10mm) in my garage that I would like to use.
Obviously and unfortunately I can't afford a Northward room hehe
Also I am moving cities and places often so I would like to have some mobile absorber modules that I can carry around if my studio moves again.

What would you suggest to do? My first idea was to make some nice superchunks, but apperently that's not a good idea..
I was also thinking of making some absorbers in the size of the Flex CL mats.
I was thinking of a sandwich absorber: 10cm sonorock, and then 10cm flex cl.
So a total depth of 20cm. Is that a better idea?

I know it's not the best solution.. but as I said. These are my circumstances.
Old 20th September 2018
  #14
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Quote:
Originally Posted by midmost View Post
Okay, you'll find me getting a bit frustrated at this point ;(
I have 5 packages of Flex CL (10mm) in my garage that I would like to use.
Obviously and unfortunately I can't afford a Northward room hehe
Also I am moving cities and places often so I would like to have some mobile absorber modules that I can carry around if my studio moves again.

What would you suggest to do? My first idea was to make some nice superchunks, but apperently that's not a good idea..
I was also thinking of making some absorbers in the size of the Flex CL mats.
I was thinking of a sandwich absorber: 10cm sonorock, and then 10cm flex cl.
So a total depth of 20cm. Is that a better idea?

I know it's not the best solution.. but as I said. These are my circumstances.
Use it as the deepest layer, soft side facing away from the wall (vacuum its surface a few times to remove all the dust in there and decrease resistance to flow a bit, place less dense layers in front of it, at least 10cm. Basically increase density as you go toward the back of the panel. 30cm deep panels would be better. Some thin airgaps would probably help a bit too.
Old 20th September 2018
  #15
vdH
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Quote:
Originally Posted by Northward View Post
Use it as the deepest layer, soft side facing away from the wall (vacuum its surface a few times to remove all the dust in there and decrease resistance to flow a bit, place less dense layers in front of it, at least 10cm. Basically increase density as you go toward the back of the panel. 30cm deep panels would be better. Some thin airgaps would probably help a bit too.
Hi Thomas,

I have built rooms with Flex CL and I really like the product, too bad they quit production...

30cm is obviously better, would do 20cm of low density and 10cm of high density or 10cm of low density and 20cm of high density?

You also talk about airgaps. Do you create those by drilling holes (dust!) through the Flex CL or, by leaving a space between the slabs (with spacers)?

vdH
Old 21st September 2018
  #16
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Quote:
Originally Posted by vdH View Post
Hi Thomas,

I have built rooms with Flex CL and I really like the product, too bad they quit production...

30cm is obviously better, would do 20cm of low density and 10cm of high density or 10cm of low density and 20cm of high density?

You also talk about airgaps. Do you create those by drilling holes (dust!) through the Flex CL or, by leaving a space between the slabs (with spacers)?

vdH
20cm of low density in front of 10cm higher density.

I meant air gaps between layers / the panels of various densities.
Old 26th September 2018
  #17
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I'll try that! Thanks Thomas.
I'll try built: Wall>Flex CL (100mm)>Thermarock 50 (100mm)>Sonorock (10mm)
So I'll go from low to high density gradually as you adviced
Old 27th September 2018
  #18
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Quote:
Originally Posted by Northward View Post
Fibers size affects the absorption coefficient substantially. For a similar resistance to flow and density, there is an increase in absorption coefficient alongside a decrease in fibers diameter.
Interesting! Could you define "substantially" a bit more precisely?

How "off" can the standard calculators be (acousticmodelling.com for example), considering that the only two variables they use are GFR and thickness?

Thanks!
Old 28th September 2018
  #19
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Quote:
Originally Posted by ReDRuMx View Post
Interesting! Could you define "substantially" a bit more precisely?

How "off" can the standard calculators be (acousticmodelling.com for example), considering that the only two variables they use are GFR and thickness?

Thanks!
I'm travelling right now - I will search in my documents for the couple graphs I have showing the differences. I remember it being in the vicinity of up to 400% more efficient (Frequency dependent data!) depending on the Denier of fibers being compared. Between 5 and 1 DPF being indeed where the "knee" of the curve is located iirc. A human hair is ca. 20 deniers.

The acoustic modelling site is great for DIY and getting a sense of what is happening when you vary the different parameters. But as soon as you're out of the fairly standard materials samples that were used to get the statistical models in the first place, take it with a grain of salt.

As a rule of thumb, the finer the fiber, the better. Sadly most of the of green materials have thicker fibers.

From the attached paper - keep in mind these studies seldom venture in the sub 100Hz region, sometimes not lower than 500hz, which is in the world of studios "where all the money goes":

"Conclusion:
The influence of various factors of a fibrous material on sound absorption is presented in this paper. Some of the important conclusions of this research are:
• sound absorption coefficient increased with a decrease in fiber diameter, micro denier fibers (less than 1 dpf) provide a dramatic increase in acoustical performance
• one of the most important qualities that influence the sound absorbing characteristics of a fibrous material is the specific flow resistance per unit thickness of the material. In general, It can be inferred that, higher airflow resistance always gives better sound absorption values but for airflow resistance higher than 1000 the sound absorption have less values because difficulty of movements sound wave through the materials
• tortuosity mainly affects the location of the quarter-wavelength peaks, whereas porosity and flow resistively affect the height and width of the peaks. It has also been said by the value of tortuosity determines the high frequency behavior of sound absorbing porous materials.
• fiber surface area and fiber size have strong influence on sound absorption properties. higher surface area and lower fiber size increases sound absorption.
• less dense and more open structure absorbs sound of low frequencies (500Hz), denser structure performs better for frequencies above than 2000 Hz.
• the creation air gap increases sound absorption coefficient values in mid and higher frequencies. At the same time, creation of airgap will have minima at various frequencies for various airgap distances.
• films such as PVC attachment increase sound absorption at low and mid frequencies at the expense of higher frequencies"


"Denier: is a unit of measurement that is used to determine the fiber thickness of individual threads or filaments used in the creation of textiles and fabrics. Fabrics with a high denier count tend to be thick, sturdy, and durable. Fabrics with a low denier count tend to be sheer, soft, and silky.

In terms of fills, in order to be considered a “microfiber” the fiber must be less than 1 denier, which is extremely fine. This gives the fill its airy weight, downy feel, and soft, silky texture. In comparison, a human hair is 20 denier, whereas Standard Fiber’s microfibers are typically 0.9 denier or less."
Attached Files
File Type: pdf 4610-4617 SEDDEQ.pdf (349.6 KB, 72 views)
Old 29th September 2018
  #20
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ReDRuMx's Avatar
Quote:
Originally Posted by Northward View Post
I'm travelling right now - I will search in my documents for the couple graphs I have showing the differences. I remember it being in the vicinity of up to 400% more efficient (Frequency dependent data!) depending on the Denier of fibers being compared. Between 5 and 1 DPF being indeed where the "knee" of the curve is located iirc. A human hair is ca. 20 deniers.

The acoustic modelling site is great for DIY and getting a sense of what is happening when you vary the different parameters. But as soon as you're out of the fairly standard materials samples that were used to get the statistical models in the first place, take it with a grain of salt.

As a rule of thumb, the finer the fiber, the better. Sadly most of the of green materials have thicker fibers.

From the attached paper - keep in mind these studies seldom venture in the sub 100Hz region, sometimes not lower than 500hz, which is in the world of studios "where all the money goes":

"Conclusion:
The influence of various factors of a fibrous material on sound absorption is presented in this paper. Some of the important conclusions of this research are:
• sound absorption coefficient increased with a decrease in fiber diameter, micro denier fibers (less than 1 dpf) provide a dramatic increase in acoustical performance
• one of the most important qualities that influence the sound absorbing characteristics of a fibrous material is the specific flow resistance per unit thickness of the material. In general, It can be inferred that, higher airflow resistance always gives better sound absorption values but for airflow resistance higher than 1000 the sound absorption have less values because difficulty of movements sound wave through the materials
• tortuosity mainly affects the location of the quarter-wavelength peaks, whereas porosity and flow resistively affect the height and width of the peaks. It has also been said by the value of tortuosity determines the high frequency behavior of sound absorbing porous materials.
• fiber surface area and fiber size have strong influence on sound absorption properties. higher surface area and lower fiber size increases sound absorption.
• less dense and more open structure absorbs sound of low frequencies (500Hz), denser structure performs better for frequencies above than 2000 Hz.
• the creation air gap increases sound absorption coefficient values in mid and higher frequencies. At the same time, creation of airgap will have minima at various frequencies for various airgap distances.
• films such as PVC attachment increase sound absorption at low and mid frequencies at the expense of higher frequencies"


"Denier: is a unit of measurement that is used to determine the fiber thickness of individual threads or filaments used in the creation of textiles and fabrics. Fabrics with a high denier count tend to be thick, sturdy, and durable. Fabrics with a low denier count tend to be sheer, soft, and silky.

In terms of fills, in order to be considered a “microfiber” the fiber must be less than 1 denier, which is extremely fine. This gives the fill its airy weight, downy feel, and soft, silky texture. In comparison, a human hair is 20 denier, whereas Standard Fiber’s microfibers are typically 0.9 denier or less."
Awesome, I'll explore it (read the paper) ASAP.

Thank you!!
Old 11th October 2018
  #21
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Quote:
Originally Posted by Northward View Post
Homatherm decided a couple weeks ago to stop all production. These products are not available anymore...

We're looking for replacements.
Hi,

Would this be a suitable material for building absorber panels (installed behind speakers for a front to back acoustic)?
Ecobati | Produit CHANVRE 100MM 1250X600

Thanx!
Old 11th October 2018
  #22
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Northward's Avatar
Quote:
Originally Posted by benoïde View Post
Hi,

Would this be a suitable material for building absorber panels (installed behind speakers for a front to back acoustic)?
Ecobati | Produit CHANVRE 100MM 1250X600

Thanx!
Probably not the best no.

There is no clear lab data per octave or 1/3 octave anyway, so I'd skip it.
Old 11th October 2018
  #23
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Quote:
Originally Posted by Northward View Post
Probably not the best no.

There is no clear lab data per octave or 1/3 octave anyway, so I'd skip it.
Thanx for the honest answer, what would you recommend then (preferably something I can easily find in Belgium)? By the way, I've recently worked at the Pro Tools studio at La Monnaie in Brussels, you did a stellar work on all accounts!
Old 11th October 2018
  #24
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Quote:
Originally Posted by benoïde View Post
Thanx for the honest answer, what would you recommend then (preferably something I can easily find in Belgium)? By the way, I've recently worked at the Pro Tools studio at La Monnaie in Brussels, you did a stellar work on all accounts!
Ha! Glad you liked La Monnaie's CR.

Did you mix 2.0 or 5.1/5.0? Very few people have access to this room

Try this:

UNIVERCELL(R) PANNEAUX

- Soprema


It's a replacement for Homatherm FLEX CL I am very much considering, with a few - but significant - differences:

- less dense @ 40-45kg/m3 instead of 60-65kg/m3
- looks to have a more even density distribution within the panel (Flex CL was getting denser from one side to the other)

Some similar points:

- high tortuosity
- at first glance fairly similar mechanical properties, despite less density
- ...green

We always had to vacuum the surface of Homatherm FLEX CL a few times to suck out all the loose dust in it and reduce surface impedance a bit, with this one it is probably not necessary.

With this product we'll have to change the tuned membranes thickness in the walls and ceiling though as this constraint layer will be different from FLEX CL with such a variation in weight etc. But unlikely to be a problem. Just some numbers re-arranging, not a re-design of process.

I'm going to try it on a couple of projects and have it tested. I have a few samples at the office and I think it will be ok for the use.
Old 12th October 2018
  #25
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Quote:
Originally Posted by Northward View Post
Ha! Glad you liked La Monnaie's CR.

Did you mix 2.0 or 5.1/5.0? Very few people have access to this room

Try this:

UNIVERCELL(R) PANNEAUX

- Soprema


It's a replacement for Homatherm FLEX CL I am very much considering, with a few - but significant - differences:

- less dense @ 40-45kg/m3 instead of 60-65kg/m3
- looks to have a more even density distribution within the panel (Flex CL was getting denser from one side to the other)

Some similar points:

- high tortuosity
- at first glance fairly similar mechanical properties, despite less density
- ...green

We always had to vacuum the surface of Homatherm FLEX CL a few times to suck out all the loose dust in it and reduce surface impedance a bit, with this one it is probably not necessary.

With this product we'll have to change the tuned membranes thickness in the walls and ceiling though as this constraint layer will be different from FLEX CL with such a variation in weight etc. But unlikely to be a problem. Just some numbers re-arranging, not a re-design of process.

I'm going to try it on a couple of projects and have it tested. I have a few samples at the office and I think it will be ok for the use.
Thanx for the links!

Yes, I had to do a live 2.0 broadcast mix for the Mozart Opera opening the season (Zauberflöte), it was a real pleasure working in that room, although space was tight because we had to fit a Lawo in the control room.
Old 22nd October 2018
  #26
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Quote:
Originally Posted by Northward View Post
...

As a rule of thumb, the finer the fiber, the better. Sadly most of the of green materials have thicker fibers ...
I keep meaning to write a reply, better late than never

What you wrote above would imply that, for a given GFR, varying fibre diameter would give different absorption properties.

The paper you posted is interesting, but I can't seem to find (or understand) this un-correlated (or at least "loose") connection between fiber diameter and GFR.

In other words -> Yes, thinner fibers means better absorptive properties (a more tortuous path), but having thinner fibers directly influences the GFR value (i.e. knowing fiber diameter is unnecessary). Quote from the paper:

"For a fibrous material with a given porosity, this means that the flow resistance per unit thickness is inversely proportional to the square of the fiber diameter."

As far as I understand, this means they are in a direct relationship, and you cannot de-correlate fiber diameter from the GFR calculation, in the same way you cannot de-correlate (e.g.) "distance" from the "speed" formula.

Changing the value of one changes the value of the other, unless some other (third) variable is also changed.

Please help me understand

Last edited by ReDRuMx; 22nd October 2018 at 10:24 PM..
Old 22nd October 2018
  #27
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From THIS paper:

Quote:
The realisation that airflow resistivity is directly linked to the acoustic properties of fibrous media allows for the measurement of both fibre diameter and material density rapidly and non-invasively from acoustical data, such as the surface impedance or absorption coefficient
and

Quote:
From these results, it could be concluded that the Miki model is superior in terms of the flow resistivity inversion when compared to the Padé approximation model, Bies-Hansen, Kozeny-Carman and Garai- Pompoli equations. It could also be said that the Bies-Hansen, Kozeny- Carman and Garai-Pompoli equations have a few significant drawbacks such as the requirement to know several material parameters in advance of the experiment. Some parameters, e.g. fibre diameter and its distribution, can be difficult to measure or to predict. Conversely, the Miki and Padé approximation models can be run, and to a good accuracy, without the knowledge of any parameter other than the material’s thickness.
Also from the original Delaney / Blazey paper - LINK:

Quote:
Now the main factors influencing the flow-resistance of fibrous materials are the fibre size and the bulk density, and it is known that for given fibre size the relation between bulk density and flow-resistance approximates closely to a simple power law.
As far as I understand all of the above, it goes in contradiction to the claim that GFR and fiber diameter can be considered separately (to whatever degree). If the "GFR to fibre diameter" relationship was "looser" than mentioned in the above quotes, it would surely deserve a mention?

Last edited by ReDRuMx; 22nd October 2018 at 09:50 PM..
Old 23rd October 2018
  #28
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Quote:
Originally Posted by ReDRuMx View Post
I keep meaning to write a reply, better late than never

What you wrote above would imply that, for a given GFR, varying fibre diameter would give different absorption properties.

The paper you posted is interesting, but I can't seem to find (or understand) this un-correlated (or at least "loose") connection between fiber diameter and GFR.

In other words -> Yes, thinner fibers means better absorptive properties (a more tortuous path), but having thinner fibers directly influences the GFR value (i.e. knowing fiber diameter is unnecessary). Quote from the paper:

"For a fibrous material with a given porosity, this means that the flow resistance per unit thickness is inversely proportional to the square of the fiber diameter."

As far as I understand, this means they are in a direct relationship, and you cannot de-correlate fiber diameter from the GFR calculation, in the same way you cannot de-correlate (e.g.) "distance" from the "speed" formula.

Changing the value of one changes the value of the other, unless some other (third) variable is also changed.

Please help me understand
See below extract from my little Excel file of products database. The rockwool is an old type ('mono' IIRC, I have to check). Data is for panels against a rigid wall. No air gap. All other things being fairly equal but fiber thickness.

Frequency 125 250 500 1000 2000 4000
WoodWool 50mm 9k Pa·s/m² 48kg/m3 0.06 0.14 0.36 0.74 0.52 0.81
Rockwool 50mm 11k Pa·s/m² 50kg/m3 0.10 0.45 0.95 0.80 0.60 1.00

The models you mention are statistical and are usually based on products with fairly similar fiber size (rockwool, glass wool etc). Parameters can seem to correlate within a specific range of fiber sizes (and materials production process) and un/de-corelate for others. Most natural fiber's denier varying from the typical rockwool denier by a very large factor. Very much outside of the realm of "classic" products variations.

The data about thicker natural fibers products etc is slowly starting to appear, but they are very much in line with the data shown here. You'll notice manufacturers tend to avoid showing the abs coeff of certain green products in their data sheets.

I'll write more when I have time.
Old 23rd October 2018
  #29
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Quote:
Originally Posted by Northward View Post
Frequency 125 250 500 1000 2000 4000
WoodWool 50mm 9k Pa·s/m² 48kg/m3 0.06 0.14 0.36 0.74 0.52 0.81
Rockwool 50mm 11k Pa·s/m² 50kg/m3 0.10 0.45 0.95 0.80 0.60 1.00
Nice, thank you, exactly what i was looking for.

GFR value, manufacturer reported?
Abs. coefficients, your measurement or manufacturer reported?
Old 23rd October 2018
  #30
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Quote:
Originally Posted by ReDRuMx View Post
Nice, thank you, exactly what i was looking for.

GFR value, manufacturer reported?
Abs. coefficients, your measurement or manufacturer reported?
I believe for rockwool it's all manufacturer data. For Wood Wool it's GFR by manufacturer and impedance tube measurements I paid for while inquiring Homatherm FLEX CL and other green products a bit over a decade ago.
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