11th May 2011

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11th May 2011

#**122**

26th December 2011

#**123**

I took my time to read this thread as i tryed to get informed to others but no results so i decided to post my thoughts here.

I am from East Europe and im building bass traps / apsorbers for my home room.

I found this two types of rock wool in my nearest building material supplyer.

Now there are few things i cant connect ,everybody is writing about density and all ,and i dont know what density should be.

Take a look at this two parameters at pictures i posted . ( Rd m2K/W and "lamda" d W/mK )

What is the density ,how are theese two products in relation of the things you have been saying ,like something with 58 kg/m3 or 100kg/m3.

Thank you in advance ,looking foward to get a reply..

Cheers

26th December 2011

#**124**

For acoustics the data we would like is Gas Flow Resistivity. However, these materials are used as thermal insulation in the real world. So they don't show GFR or even Density sometimes.

I can't even read the small print on those photos. Look up the manufacturers Data sheets or ask them about density.

703 is about 50KG per Cubic Metre. 705 is about 100KG.

Things don't need to be exact at all.

DD

I can't even read the small print on those photos. Look up the manufacturers Data sheets or ask them about density.

703 is about 50KG per Cubic Metre. 705 is about 100KG.

Things don't need to be exact at all.

DD

28th December 2011

#**125**

True ,but it also says it is in use for thermal insulation and acoustic as well ,

Looks like i should really do that ,again if any of you guys can explain and compare my data from those 2 pics i uploaded to like 703 and 705 i would be glad

Wonder what settings of rockwool would be allright for mic screen purpose ? hm

10th January 2012

#**126**

Quote:

First of all, hello everyone. I'm new here. Really helpful forum.

As it has been stated above, gas flow resistivity is the most important factor when it comes to sound absorption.

The densities are for those products are:

ROCKWOOL STEPROCK - C

According to the graphs below, air flow resistivity should be 70.000 MKS Rayls/m = 70.000 KPa.s/m2

ROCKWOOL MULTIROCK - C

According to the graphs below, air flow resistivity should be 8.000 MKS Rayls/m = 8.000 KPa.s/m2 roughly equivalent to a lower-density OC 701 - should be 18 kg/m3.

Owens Corning 700 Series specific density and air flow resistance. Density is taken from data sheets. I copied the Air flow resistance from one of Avare's posts dating back to 2008, when he mailed Owens Corning asking for the information. So It's not published official information (from what I gather, NASA measured the 703 to be 24.000 MKS Rayls/m)

OC 701 1.5 pcf = 24 kg/m3 = 8.000 MKS Rayls/m = 8.000 K Pa.s/m2

OC 703 3.0 pcf = 48 kg/m3 = 16.000 MKS Rayls/m = 16.000 K Pa.s/m2

OC 705 6.0 pcf = 96 kg/m3 = 30.000 MKS Rayls/m = 30.000 K Pa.s/m2

OC 707 7.0 pcf = 112 kg/m3

As a general rule of the thumb, in East Europe, Rockwool has the following system for describing density:

ROCKWOOL AIRROCK ND NORMAL DENSITY- 50 kg/m3 - roughly equivalent to OC 702

ROCKWOOL AIRROCK HD HIGH DENSITY - 70 kg/m3 - roughly equivalent to OC 703

ROCKWOOL AIRROCK XD EXTREME DENSITY- 90 kg/m3 - roughly equivalent to OC 704

All of these equivalents are based on the two graphs below. Please correct me if I'm wrong.

The examples above are referring to a "general building" product, but I suspect it's mostly the same as the better-known Rockwool RW series, measured in Bob Gold's Absorption Coefficients Table

Rockwool RWA45 = 45 kg/m3

Rockwool RW3 = 60 kg/m3

Rockwool RW5 = 100 kg/m3

Rockwool RW6 = 140 kg/m3

Quoting Scott R. Foster:

"...rockwool requires a higher density because of the nature of the material. Generally you could expect similar acoustic performance with a panel about 50% denser in grade [this would approximately match the gas flow properties of 703] which works out to about 5 lbs. per cubic foot or about 60 kg/m3. But even at this density rockwool has inferior handling properties to 703 and yields a heavier panel [no biggy for a hang forget application, but if portability matters this is a flaw]."

Quoting Andre Vare:

"Rockwool is broady equivalent at slightly denser at around 48 kg/m^3 fiberglas at 64 kg/m^3. the relationship acoustically is not linear."

Some useful graphs - I thing I saw them posted somewhere on the forum before, sorry for the redundancy but I believe they're important:

Source: Rockwool Marine & Offshore Acoustic Manual - Highly recommended reading

Source: Building Acoustics, author Tor Erik Vigran

10th January 2012

#**127**

Here's a very well written post from Hannes.

Note however he uses 16000 for OC703, while NASA regarded it as 27,000.

He then regards 705 as 45000, which ties in with NASA if one were to guess, but does not tie in with OC published 30000 or the 70000 from the graphs.

So, perhaps most of the confusion is to do with OC's released figures.

https://www.gearslutz.com/board/6328646-post88.html

The graphs show a fairly linear relationship, I expect that is a prediction, not a set of measured results.

Common Gas Flow Resistivity numbers.

Here's a load of published GFRs. Common Gas Flow Resistivity numbers.

I was thinking about compiling all the say 50KG products to see what the range of GFR's is.

I suspect it is surprisingly broad.

DD

Note however he uses 16000 for OC703, while NASA regarded it as 27,000.

He then regards 705 as 45000, which ties in with NASA if one were to guess, but does not tie in with OC published 30000 or the 70000 from the graphs.

So, perhaps most of the confusion is to do with OC's released figures.

https://www.gearslutz.com/board/6328646-post88.html

The graphs show a fairly linear relationship, I expect that is a prediction, not a set of measured results.

Common Gas Flow Resistivity numbers.

Here's a load of published GFRs. Common Gas Flow Resistivity numbers.

I was thinking about compiling all the say 50KG products to see what the range of GFR's is.

I suspect it is surprisingly broad.

DD

10th January 2012

#**128**

28th October 2016

#**130**

Quote:

Looks like we're neighbours (I'm from Romania)

First of all, hello everyone. I'm new here. Really helpful forum.

As it has been stated above, gas flow resistivity is the most important factor when it comes to sound absorption.

The densities are for those products are:

ROCKWOOL STEPROCK - C**120 KG/M3** meant for floor insulation - reduces impact noise (footsteps, etc.)

According to the graphs below, air flow resistivity should be 70.000 MKS Rayls/m = 70.000 KPa.s/m2**roughly equivalent to OC 705 96 kg/m3** glass wool.

ROCKWOOL MULTIROCK - C**28 KG/M3** meant for general thermal insulation

According to the graphs below, air flow resistivity should be 8.000 MKS Rayls/m = 8.000 KPa.s/m2 roughly equivalent to a lower-density OC 701 - should be 18 kg/m3.

Owens Corning 700 Series specific density and air flow resistance. Density is taken from data sheets. I copied the Air flow resistance from one of Avare's posts dating back to 2008, when he mailed Owens Corning asking for the information. So It's not published official information (from what I gather, NASA measured the 703 to be 24.000 MKS Rayls/m)

OC 701 1.5 pcf = 24 kg/m3 = 8.000 MKS Rayls/m = 8.000 K Pa.s/m2

OC 703 3.0 pcf = 48 kg/m3 = 16.000 MKS Rayls/m = 16.000 K Pa.s/m2

OC 705 6.0 pcf = 96 kg/m3 = 30.000 MKS Rayls/m = 30.000 K Pa.s/m2

OC 707 7.0 pcf = 112 kg/m3

As a general rule of the thumb, in East Europe, Rockwool has the following system for describing density:

**ROCKWOOL AIRROCK LD LOW DENSITY - 40 kg/m3 - roughly equivalent to OC 701 or 711**

ROCKWOOL AIRROCK ND NORMAL DENSITY- 50 kg/m3 - roughly equivalent to OC 702

ROCKWOOL AIRROCK HD HIGH DENSITY - 70 kg/m3 - roughly equivalent to OC 703

ROCKWOOL AIRROCK XD EXTREME DENSITY- 90 kg/m3 - roughly equivalent to OC 704

All of these equivalents are based on the two graphs below. Please correct me if I'm wrong.

The examples above are referring to a "general building" product, but I suspect it's mostly the same as the better-known Rockwool RW series, measured in Bob Gold's Absorption Coefficients Table

Rockwool RWA45 = 45 kg/m3

Rockwool RW3 = 60 kg/m3

Rockwool RW5 = 100 kg/m3

Rockwool RW6 = 140 kg/m3

Quoting Scott R. Foster:

"...rockwool requires a higher density because of the nature of the material. Generally you could expect similar acoustic performance with a panel about 50% denser in grade [this would approximately match the gas flow properties of 703] which works out to about 5 lbs. per cubic foot or about 60 kg/m3. But even at this density rockwool has inferior handling properties to 703 and yields a heavier panel [no biggy for a hang forget application, but if portability matters this is a flaw]."

Quoting Andre Vare:

"Rockwool is broady equivalent at slightly denser at around 48 kg/m^3 fiberglas at 64 kg/m^3. the relationship acoustically is not linear."

Some useful graphs - I thing I saw them posted somewhere on the forum before, sorry for the redundancy but I believe they're important:

Source: Rockwool Marine & Offshore Acoustic Manual - Highly recommended reading

Source: Building Acoustics, author Tor Erik Vigran

First of all, hello everyone. I'm new here. Really helpful forum.

As it has been stated above, gas flow resistivity is the most important factor when it comes to sound absorption.

The densities are for those products are:

ROCKWOOL STEPROCK - C

According to the graphs below, air flow resistivity should be 70.000 MKS Rayls/m = 70.000 KPa.s/m2

ROCKWOOL MULTIROCK - C

According to the graphs below, air flow resistivity should be 8.000 MKS Rayls/m = 8.000 KPa.s/m2 roughly equivalent to a lower-density OC 701 - should be 18 kg/m3.

Owens Corning 700 Series specific density and air flow resistance. Density is taken from data sheets. I copied the Air flow resistance from one of Avare's posts dating back to 2008, when he mailed Owens Corning asking for the information. So It's not published official information (from what I gather, NASA measured the 703 to be 24.000 MKS Rayls/m)

OC 701 1.5 pcf = 24 kg/m3 = 8.000 MKS Rayls/m = 8.000 K Pa.s/m2

OC 703 3.0 pcf = 48 kg/m3 = 16.000 MKS Rayls/m = 16.000 K Pa.s/m2

OC 705 6.0 pcf = 96 kg/m3 = 30.000 MKS Rayls/m = 30.000 K Pa.s/m2

OC 707 7.0 pcf = 112 kg/m3

As a general rule of the thumb, in East Europe, Rockwool has the following system for describing density:

ROCKWOOL AIRROCK ND NORMAL DENSITY- 50 kg/m3 - roughly equivalent to OC 702

ROCKWOOL AIRROCK HD HIGH DENSITY - 70 kg/m3 - roughly equivalent to OC 703

ROCKWOOL AIRROCK XD EXTREME DENSITY- 90 kg/m3 - roughly equivalent to OC 704

All of these equivalents are based on the two graphs below. Please correct me if I'm wrong.

The examples above are referring to a "general building" product, but I suspect it's mostly the same as the better-known Rockwool RW series, measured in Bob Gold's Absorption Coefficients Table

Rockwool RWA45 = 45 kg/m3

Rockwool RW3 = 60 kg/m3

Rockwool RW5 = 100 kg/m3

Rockwool RW6 = 140 kg/m3

Quoting Scott R. Foster:

"...rockwool requires a higher density because of the nature of the material. Generally you could expect similar acoustic performance with a panel about 50% denser in grade [this would approximately match the gas flow properties of 703] which works out to about 5 lbs. per cubic foot or about 60 kg/m3. But even at this density rockwool has inferior handling properties to 703 and yields a heavier panel [no biggy for a hang forget application, but if portability matters this is a flaw]."

Quoting Andre Vare:

"Rockwool is broady equivalent at slightly denser at around 48 kg/m^3 fiberglas at 64 kg/m^3. the relationship acoustically is not linear."

Some useful graphs - I thing I saw them posted somewhere on the forum before, sorry for the redundancy but I believe they're important:

Source: Rockwool Marine & Offshore Acoustic Manual - Highly recommended reading

Source: Building Acoustics, author Tor Erik Vigran

ISOVER /SAINT GOBAIN:

ISOVER EXTRAWALL 4+ con density 40 kg/m3

E100 S con density 50 kg/m3W/mK,

CLIMA 34 con density 55 kg/m3

28th October 2016

#**131**

Quote:

"OC 703 3.0 pcf = 48 kg/m3 = 16.000 MKS Rayls/m = 16.000 K Pa.s/m2"

But anyway... why are you digging up a 4 year old thread? :P

28th October 2016

#**132**

6th June 2019

#**133**

Quote:

Porous Absorber Calculator is your best friend.

I need to make a keyboard macro with that sentence.

Dammit, is it so difficult do download the bloody thing and insert some bloody numbers?

OK, here are some values as being written in my secret documents (no actually derived from Porous Absorber Calculator, hehe) for 48 Hz. Served on a silver tablet:

10 cm absorption, 10 cm gap, 16800 Pa*s/m²:

**27 % absorption (equals a resulting dip of - 5.7 dB ***per wall *for an uneven mode)

30 cm absorption 5000 Pa*s/m², 20 cm gap:

**60 % absorption (equals -2.2 dB)**

30 cm absorption 5000 Pa*s/m², 40 cm gap:

**68 % absorption (equals - 1.7 dB)**

60 cm absorption 2000 Pa*s/m², 50 cm gap:

**85 % absorption (equals - 0.7 dB)**

All values given for normal incidence. Porous Absorption Calculator is based on the formulas of Delany and Bazley and requires the gas flow resistivity to be between 1000 Pa*s/m² and 50000 Pa*s/m² (as is the case here).

Hannes

I need to make a keyboard macro with that sentence.

Dammit, is it so difficult do download the bloody thing and insert some bloody numbers?

OK, here are some values as being written in my secret documents (no actually derived from Porous Absorber Calculator, hehe) for 48 Hz. Served on a silver tablet:

10 cm absorption, 10 cm gap, 16800 Pa*s/m²:

30 cm absorption 5000 Pa*s/m², 20 cm gap:

30 cm absorption 5000 Pa*s/m², 40 cm gap:

60 cm absorption 2000 Pa*s/m², 50 cm gap:

All values given for normal incidence. Porous Absorption Calculator is based on the formulas of Delany and Bazley and requires the gas flow resistivity to be between 1000 Pa*s/m² and 50000 Pa*s/m² (as is the case here).

Hannes

I don't quite get what Hannes is saying here. Or, I'd like to confirm that I'm interpreting this correctly:

Higher percentages of absorption means less attenuation in dB? (see the bold text in the quoted post).

I'm concidering building a Helmholtz absorber for 37Hz (fundamental axial mode in my room) and I used the Helmholtz Absorber Calculator to get an idea of what I would need (see attached image).

So, relating to the above, an absorption of almost 1 would mean very little attenuation? E.G. useless? Doesn't make sense to me... But I could be wrong. Can someone please clarify?

6th June 2019

#**134**

what I wrote only applies to absorption, and there only in the case when you have the thickness of the absorbing panel as a free parameter of your choice. A Helmholtz absorber is an entirely different topic, so let not yourself confuse with what I wrote above.

Hope this helps

Hannes

6th June 2019

#**135**

Quote:

what I wrote only applies to absorption, and there only in the case when you have the thickness of the absorbing panel as a free parameter of your choice. A Helmholtz absorber is an entirely different topic, so let not yourself confuse with what I wrote above.

Hope this helps

Hannes

But that doesn't explain why a high absorption figure equates to lower attentuantion in dB. Unless I'm misinterpreting your post.

6th June 2019

#**136**

Quote:

In general, higher absorption figures should be related to higher attenuation.

6th June 2019

#**137**

2 weeks ago

#**138**

2 weeks ago

#**139**

Quote:

This is false: Bigger gas flow resisitivity is always better for absorbing low frequencies.

This is false: Lower gas flow resistivity is always better for absorbing low frequencies.

This is true: For each combination of air gap, absorber thickness, chosen frequency and geometry (wall, wall-corner, corner-corner) there is an optimal gas flow resisitivity. If we go higher or lower from there, we loose absorption.

So I think that OC 705 is a good material for

Think about this analogy: We fire with rubber bullets on targets made from different material. Let us say the thickness of the target is relatively thin and the target gives very low resistance, like wool or paper. Then most of the bullets will penetrate the target, bounce at the wall behind and penetrate again. No much effect.

Now we take a material that gives more resistance. With that we can catch more of the bullets, but quite a portion will be reflected.

If we now allow ourselves to have a thicker target then the lighter material may become more useful again. Because of its thickness, more bullets will be caught than before, but because the material is soft the reflection is very low. The overall absorption we can achieve with that material is better than with the denser material.

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