Rockwool

[ThomasT]

Hi,

there are different products of rockwool (e.g. sonorock, floorrock).

What product is suitable for what application?
Rockwool is cheaper than fiberglas for me.
They don't print any density or absorbtion coefficient on their data sheets.

For instance, is a sheet of 30mm-floorrock usable as bass hanger?

Thomas

[carsten_d]

floorrock is high density stuff.
xtreme compressed.
i would say it's not that good for bass hangers.

try to find weichfaserdämmplatten and use sonorock.
i think this is what john always suggests.

somewhere in the acoustics forum is a great thread about bass hangers i think
it was this thread

carsten

[ThomasT]

floorrock is high density stuff.
xtreme compressed.
i would say it's not that good for bass hangers.

try to find weichfaserdämmplatten and use sonorock.
i think this is what john always suggests.

Im glad to had someone on the telefon from rockwool that could give some more specific answers.
At first rockwool does not measure any absorbtion coefficents like ovens corning or other manufactures of fiberglas did.

floorrock has 100kg/m³
sonorock has 30kg/m³
flexirock has 60kg/m³

But he suggested http://produktwegweiser-rocknavi.rockwo ... %20raf.pdf.
Doesn't look that nice to me.

Greetings Thomas

[Soundman2020]

Normal recommendation here is for 48 kg/m³, so based on that the "Flexirock" product seems to be the closest match, at 60kg/m³. That should probably do the job reasonably well. IMHO

- Stuart -

[ThomasT]

Hi,

but flexirock is doubled expensive. Sonorock is around 40 Euros/m³, flexirock 80 Euros/m³.
Will Sonorock (30kg/m³) work for absorber panels and "super chunks"?

Thomas

[Ro]

yes, that will work too. You see density isn't the most important factor in building a good absorber, it's generly the depth that will have the most significant impact.

48kg/m3 is most recommended since it has best overall absorption but it isn't a strickt rule.

If you go supperchunk, assuming you want a low-end absorber, make it as thick/deep as you can affort (in a corner, 50x50cm wide will do already) Put a "filter" in front to keep it from sucking too much high frq as well. Read the board and you'll understand.
check http://www.johnlsayers.com/phpBB2/viewt ... 10&t=12321

[orangenumerik]

Put another way...allowing a lighter density material (say, batts of rockwool) to occupied more space will give better absorbtion figures than higher density using less space.

[Soundman2020]

allowing a lighter density material (say, batts of rockwool) to occupied more space will give better absorbtion figures than higher density using less space.

True! But speaking of picky ( ), there's also the issue of diminishing returns: once the density gets too low, it stops being effective. Just as when the density gets too high.

[valentin]

Hope this helps

In recent discussions with Dr. Peter D’Antonio, he said the following:
For optimal absorption, a porous absorber should offer a surface impedance with a lowfl
ow resistivity, which matches that of air to remove refl ections, while offering a high
internal acoustic attenuation. When attempting to control refl ections with a single
density material, it is fair to say that thin fi berglass panels should not be used, and in
my view lower density is preferred over higher density. In addition, thicker panels and a
rear air cavity both contribute to extending the absorption to lower frequencies.
When it comes to sound absorption, it could be useful to ask what is used
in anechoic chambers, where the goal is complete elimination of sound above
a certain “cut-off” frequency. In traditional designs, the wedge-shaped absorbers
must be at least 1/4-wavelength long at the lowest frequency of interest. In good
chambers, this is typically 3 to 4 ft (0.9 to 1.2 m). The material used in these
wedges is usually compressed glass fi ber with a density of about 3 pcf (48 kg/m3).
According to one study, that density appears to have been a choice of convenience
(structural rigidity and particle shedding considerations) because a lowerdensity
material (1.1 pcf, 18 kg/m3) was closer to the acoustical target performance
(Koidan et al., 1972). Rasmussen (1972) describes an anechoic chamber constructed
of suspended cubes, somewhat randomly arranged with small (2-in.,
50 mm) low-density (1.9 pcf, 30 kg/m3) cubes farthest from the wall and progressively
larger, denser cubes placed closer to the wall, with the inner layer being
Acoustical Performances of Some Common Materials 6 to 7.5 pcf (100–120 kg/m3) stacked against the wall.
It apparently worked superbly.
In summary, all of this suggests that the surface of the absorbing material—
the interface with the sound fi eld—should have relatively low density and that
to achieve performance at lower frequencies, one may need to seriously consider
how much real estate can be devoted to the task because materials that work well
have appreciable thickness.