4'' Rockfon ceiling tiles, works as OC703/705 with membrane?

[tlindaas]

I have heard good things about using thick ceiling tiles for bass traps. The thickness (and density) make them absorb bass well, and the somewhat hard surfaces make them non-sagging, maybe even stackable, and somewhat reflective in the mid/highs. If you want less reflectivity, just apply some soft fabric on top. If you want more, apply a harder surface, like thin plastic. You can still make it look good by wrapping some form of cloth over the plastic.

These particular ones I'm looking at (Rockfon Industrial) are 70 kg/m3, so they fall inbetween the density of OC703 and OC705. I'm thinking of stacking them on top of each other, or put them into bookshelfs against the wall, and to cut them into superchunks in the corners.

It seems to me that they basically will function like Realtraps non-HF minitraps/mondotraps, which are made of similiar material and have a reflective plastic surface on top (beneath the cloth). Am I mistaken in this assumption?

More info here: Industrial Opal, 1200x600 A24 100mm System SY24 (T24) : Rockfon

[avare]

Where to start. Denser is not better for bass absorption in and of itself. The absorption data shows a lLOF rollof staring well before it does with 703/705. Without further testing, I do not recommend it.

Andre

[tlindaas]

I'm no expert reading these graphs and tables, but I can see what you mean regarding density/absorption. But would you agree that Rockfon Industrial has roughly 2/3 of the bass performance of OC703/705? For instance, Rockfon 10cm (4''), plus 10cm air, is 0.55 at 125hz, while OC703/705 on wall is 0.84/0.75, and with 16'' air 0.65/0.59. http://www.bobgolds.com/AbsorptionCoefficients.htm

When some material is inferior, can you compensate by making it thicker? So if the performance is roughly 2/3, can you compensate by adding 1/3 to the depth? Just askin..

I'm interested in alternatives because I can't buy Owens Corning insulation where I live (Norway). The Rockfons is the closest, to my knowledge. If anybody knows something better, please share!

[avare]

Originally Posted by tlindaas

I'm no expert reading these graphs and tables, but I can see what you mean regarding density/absorption. But would you agree that Rockfon Industrial has roughly 2/3 of the bass performance of OC703/705? For instance, Rockfon 10cm (4''), plus 10cm air, is 0.55 at 125hz, while OC703/705 on wall is 0.84/0.75, and with 16'' air 0.65/0.59. http://www.bobgolds.com/AbsorptionCoefficients.htm

When some material is inferior, can you compensate by making it thicker? So if the performance is roughly 2/3, can you compensate by adding 1/3 to the depth? Just askin..

No, it is not that simple. It is dependent on the materials gas flow resistivity, porosity, fiber length and other characteristics of the material. The deviation of the material you linked could be a different binder and amount used.

Andre

[tlindaas]

Originally Posted by avare

No, it is not that simple. It is dependent on the materials gas flow resistivity, porosity, fiber length and other characteristics of the material. The deviation of the material you linked could be a different binder and amount used.

Andre

So density, gas flow resistivity, porosity, fiber lenght, binder all contribute to performance? If so, it seems really hard to predict the performance of a non-tested material, since only density - occasionally - gets mentioned in the literature. From what I've seen at least.

I've read some more on Bob Golds web page for absorption coefficients for different materials, and it seems that Rockwool RHT 40 for shorter dephts, and Rockwool RW2 for longer, are good choices. Problem is, these materials don't exsist where I live (I googled, nothing). So I should probably call the local Rockwool office and see if they know anything. Yea, I'll do that tomorrow..

[avare]

Originally Posted by tlindaas

So density, gas flow resistivity, porosity, fiber lenght, binder all contribute to performance? If so, it seems really hard to predict the performance of a non-tested material, since only density - occasionally - gets mentioned in the literature. From what I've seen at least.

I've read some more on Bob Golds web page for absorption coefficients for different materials, and it seems that Rockwool RHT 40 for shorter dephts, and Rockwool RW2 for longer, are good choices. Problem is, these materials don't exsist where I live (I googled, nothing). So I should probably call the local Rockwool office and see if they know anything. Yea, I'll do that tomorrow..

Yes it is difficult without more information than the type of material and densityl.

Good luck with your queries and let us what you find! It will help other people from Norway.

A fellow Scandinavian (Estonian),
Andre

[kasmira]

Originally Posted by tlindaas

So density, gas flow resistivity, porosity, fiber lenght, binder all contribute to performance? If so, it seems really hard to predict the performance of a non-tested material, since only density - occasionally - gets mentioned in the literature. From what I've seen at least.

Exactly. This is why so many of the "go-to-materials" are recommended. They have been tested, tested, and tested, so its easy to get measurements on them. Otherwise its extremely hard to tell what will happen when you place something else in the room. Of course, if you want to make 4" panels of ceiling tiles and test them, showing us what they can do for your room...

When I found insulation in my city, I originally called a supplier who only sells to contractors, but he gave me the number to a distributor who gave me amazing prices. Best of luck!

[tlindaas]

Originally Posted by avare

Good luck with your queries and let us what you find! It will help other people from Norway.

If I get the chance to talk to a technically competent person, is there anything in particular I should ask for, to get information on acoustically relevant products other than possible equivalents for RW2 and RHT 40?

For instance, is gas flow resistivity like "the most important property" when it comes to which frequencies gets absorbed and how much, or are the other properties (porosity, fiber lenght, binder) just as important? The more complex this is, the harder it will be to get good answers, I suppose.

[tlindaas]

It seems that there is a loose, but consistent relationship between gas flow resistivity and density (look at the graph):

Airflow Resistance - Rockwool Marine & Offshore

After many calls and emails, I have still no good acoustically relevant data for specific products to share here. But I'm not giving up just yet. On Rockwool's home page they state that all the data we are interested in here is available:

"Stiffness, airflow resistance and other properties linked to the acoustic performance of a mineral wool product mainly depend on the bulk density, fibre orientation, fibre diameter, binder and possible additives. Rockwool can specify all these parameters in a wide range depending on the desired properties. "

Fibre Diameter and Fibre Orientation - Rockwool Marine & Offshore

[avare]

Originally Posted by tlindaas

It seems that there is a loose, but consistent relationship between gas flow resistivity and density (look at the graph):

Airflow Resistance - Rockwool Marine & Offshore

After many calls and emails, I have still no good acoustically relevant data for specific products to share here. But I'm not giving up just yet. On Rockwool's home page they state that all the data we are interested in here is available:

"Stiffness, airflow resistance and other properties linked to the acoustic performance of a mineral wool product mainly depend on the bulk density, fibre orientation, fibre diameter, binder and possible additives. Rockwool can specify all these parameters in a wide range depending on the desired properties. "

Fibre Diameter and Fibre Orientation - Rockwool Marine & Offshore

Nice links. Thank you. If you are interested in more on the physical properties that affect sound absorption of porous materials, the document I u/led in post #53 in this thread is good.

We have have had great succees at finding the black hole of knowledge about the acoustic related properties of Roxul products. This black hole exists despite Roxul Marine publishing a great manual on their products and what the significant characteristcs are. The document is linked in my resource post in acoustics/reference sticky.

Good luck!

Andre

[tlindaas]

Originally Posted by avare

This black hole exists despite Roxul Marine publishing a great manual on their products and what the signiifcant characteristcs are. The document is linked in my resource post in acoustics/reference sticky.
Andre

Could not find your link. But is this the document?

http://www.international.rockwool-ma...c%20Manual.pdf

[avare]

Originally Posted by tlindaas

Could not find your link. But is this the document?

http://www.international.rockwool-ma...c%20Manual.pdf

Yes it is. For more great documents at the right price, here is my post.

Freely,
Andre

[tlindaas]

Found a PDF which concludes that the ISO 354 sound absorption measurement standard, commonly used in Europe, gives less impressive numbers for bass and low mids performance, compared to the ASTM C423 standard commonly used in USA:

"To a specifier of ceilings, the same material could appear to be less effective when the sound absorption is reported using the ISO method."

The test samples were all thinner than 1 inch, there was a 400mm air gap, and max difference in absorption coefficient between the standards was 0.12.

http://intellagence.eu.com/acoustics...les/001547.pdf

Update: Auralex says the same thing:

"[...] there are three main standard methods used to test materials for absorption. Two of
them are reverberation chamber methods – ASTM C423 in the U.S.A. and ISO 354 in
Europe. These two methods are quite similar, but the ISO method – in general – will
produce slightly lower overall numbers than the ASTM method."

See "Absorption Coefficient (a)" here: http://www.auralexelite.com/resource...r/glossary.asp