Q 4 Avare

[DanDan]

You pose some little puzzlers.
e.g. Was that Isover HPDS measured with the foil facing out or in?
Is the MHOA graph really true?
While there may be a tag game between density and gas flow resistivity, does this automatically mean a similar relationship between density and absorption, or between gfr and absorption? There's a proper Q4Avare!

I may have posted these here already but no matter.
Much can be explored using sample GFRs Common Gas Flow Resistivity numbers.
and a Calculator Porous Absorber Calculator

The Ecose stuff is nice. I can't read Norwegian, but that Space Slab looks like Universal Slab to me. They use different names in different territories. I would have no problem just choosing one of those, simply by density price and availability.

What seems intuitive to me is that thickness can outweigh small differences in absorption. Maybe if the insulation is really thick, like 30 cm, and if you stay in the ballpark of "light and fluffy" insulation, the acoustical differences between the different brands gets really small?

I agree.

DD

[darkbuddha]

Originally Posted by DanDan

I may have posted these here already but no matter.
Much can be explored using sample GFRs Common Gas Flow Resistivity numbers.
and a Calculator Porous Absorber Calculator

Coincidentally, I found those links another way earlier today and spent some time with them. I was pretty psych'd initially but then became a bit confused and frustrated by a few things, not the least of which is the variety of GFRs listed for OC703... 16000, 23400, 27000 (c/o NASA!). And then using the calculator, I was frustrated to find that it isn't capable of calculating for layers with differing GFRs within the same absorber (which is a question that has come up several times according to my searches). Kinda a bummer.

This also lead me to a search for off axis GFRs (as in the NASA study) and GFRs for side-incidence (as opposed to face). Interesting stuff when considering the building of super chunk traps where the material (commonly mineral wool) is presented with side-incidence, especially in comparison to the performance (and GFRs) of low density pink-fluffy stuff.

No real point to this other than I really appreciated the discussions being had and my new found fascination. Thanks all.

[tlindaas]

For the fellow noobs, here is a post on gas flow resistivity that is very to the point and easy to understand:

Knauf tp 416 ecose insulation.

[localhost127]

Originally Posted by darkbuddha

And then using the calculator, I was frustrated to find that it isn't capable of calculating for layers with differing GFRs within the same absorber (which is a question that has come up several times according to my searches). Kinda a bummer.

Software - AFMG SoundFlow

[DanDan]

That Hannes link is awesome.

SoundFlow appears to be top dog.
But for those without PC's this one does layers and Random Incidence plus
Porous Absorber Calculator
DD

[tlindaas]

Originally Posted by DanDan

SoundFlow appears to be top dog.

SoundFlows web page (click on Features) say: "Expandable database of about 150 acoustic materials."

Does that database contain gas flow resistivity for insulation products like Rockwool, Isover, Knauf?

[DrFrankencopter]

Originally Posted by DanDan

You pose some little puzzlers.
e.g. Was that Isover HPDS measured with the foil facing out or in?
Is the MHOA graph really true?
While there may be a tag game between density and gas flow resistivity, does this automatically mean a similar relationship between density and absorption, or between gfr and absorption? There's a proper Q4Avare!

I may have posted these here already but no matter.
Much can be explored using sample GFRs Common Gas Flow Resistivity numbers.
and a Calculator Porous Absorber Calculator

I compiled some of the published data for 1" thickness porous absorbers in the graph that I attached in this post: Owens Corning 705 and 707 and is king!

Another gem in that thread was posted by Avare: http://www.gearslutz.com/board/attac...617-seddeq.pdf Here's a notable quote from that paper regarding density:

Density:
Density of a material is often considered to be the important factor that governs the sound absorption behavior of the material. At the same time, cost of an acoustical material is directly related to its density. A study by Koizumi et al. (2002) showed the increase of sound absorption value in the middle and higher frequency as the density of the sample increased. The number of fibers increases per unit area when the apparent density is large. Energy loss increases as the surface friction increases, thus the sound absorption coefficient increases.
Moreover, they showed the following effect of density on sound absorption behavior of nonwoven fibrous materials.
• Less dense and more open structure absorbs sound of low frequencies (500Hz).
• Denser structure performs better for frequencies above than 2000 Hz.

The paper's conclusions are also worth quoting:

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

Cheers

Kris

[darkbuddha]

Originally Posted by DanDan

SoundFlow appears to be top dog.
But for those without PC's this one does layers and Random Incidence plus
Porous Absorber Calculator
DD

But...

Originally Posted by darkbuddha

it isn't capable of calculating for layers with differing GFRs within the same absorber

[prairiedog]

Originally Posted by darkbuddha

And then using the calculator, I was frustrated to find that it isn't capable of calculating for layers with differing GFRs within the same absorber (which is a question that has come up several times according to my searches). Kinda a bummer.

I had forgotten about that limitation. I deliberately limited each absorber to a single GFR because of some strange results I found whilst testing the software. I have since explained those results but forgot to remove the limitation. I have now removed it. Please feel free to contact me if you have any other problems.

I don't want to go off topic, but for anyone interested, here are the results I had problems with.

Interesting results

The graph shows that you can often get better low frequency absorption from a porous absorber by adding a thin layer of high resistivity material to the front.

Thanks Demetris

[tlindaas]

Thanks for the calculator Demeteris! Is there a recommended model/formulae?

[avare]

Originally Posted by DanDan

That Hannes link is awesome.

+1!

Full of gas,
Andre

[avare]

Originally Posted by prairiedog

The graph shows that you can often get better low frequency absorption from a porous absorber by adding a thin layer of high resistivity material to the front.

Yes. This is a technique used by BBC decades ago an documented in an RD report!

Well aged,
Andre

[darkbuddha]

Originally Posted by prairiedog

I had forgotten about that limitation. I deliberately limited each absorber to a single GFR because of some strange results I found whilst testing the software. I have since explained those results but forgot to remove the limitation. I have now removed it. Please feel free to contact me if you have any other problems.

I don't want to go off topic, but for anyone interested, here are the results I had problems with.

Interesting results

The graph shows that you can often get better low frequency absorption from a porous absorber by adding a thin layer of high resistivity material to the front.

Thanks Demetris

Woohoo! Thanks a ton, because it was exactly that (higher resistivity layer over lower resistivity layer, with and without air gaps) which I wanted to calculate for. Very very very cool.

[DanDan]

Sorry about the double link buddha. However I am confused.
I can do layers with different GFRs in that calculator.
Have I developed SuperPowers?


SuperDan

[darkbuddha]

Originally Posted by DanDan

Sorry about the double link buddha. However I am confused.
I can do layers with different GFRs in that calculator.
Have I developed SuperPowers?

Well now you can... read a few posts up where Demetris (prairiedog) just removed the limitation.

[DanDan]

Aaaah. Thank you both.
DD

[prairiedog]

Originally Posted by tlindaas

Thanks for the calculator Demeteris! Is there a recommended model/formulae?

"Miki" and "Allard/Champoux" are good choices. They both give reasonably accurate results over a wide range of input parameters.

Demetris

[tlindaas]

Originally Posted by tlindaas

SoundFlows web page (click on Features) say: "Expandable database of about 150 acoustic materials."

Does that database contain gas flow resistivity for insulation products like Rockwool, Isover, Knauf?

I downloaded the demo. There are air flow resistivity numbers for a few German Rockwool products, and a lot of non-insulation materials. All the Rockwool numbers are available on Rockwool's German home page.

Update: There are some generic (no product type or number provided), and some obscure insulation products under the Edit Layer Properties option. Nothing useful, though.

[kasmira]

Randomly bumping an awesome thread.