Hi,

In order to build bass traps (or broadband, whatever the difference is)
I'm looking at buying Rockwool plates 120x60x15 95 kg m^3 which have a 15 mm layer on one side which is 185 kg m^3.

For convenience that is approx. 47"x24"x6"

Which side should I use against the wall? Would 185 be too much, thus reflecting frequencies? Would it be fine if I face the denser side against the wall?

Also, is it generally better to have a trap faced over the corner rather than cutting triangles of the rockwool and stacking them in the corner?

Thanks for helping out!

Regards
Fredrik

If you can find the linear gas flow resistivity of the materials I can help you out with a calculation.

The general answer on your question is that every rockwool is reflecting to a certain amount.

I can't seem to find that number. The only specifications I have access to are these RockTorv :: Byggisolering :: Produkter :: AS Rockwool, but unfortunately it's in norwegian.

When you say that in general rockwool reflect. What frequencies are we talking about?

Thank you for helping out

FHL, most of these materials are optimized for maximizing transmission loss in conjunction with a gypsum board wall. That is what they are made for.

What we need is minimizing the reflection which is a total different topic alltogether.

Your material will have a reflection coefficient of about 75 % at 50 Hz. I PM you some more info.

Thank you very much, Hannes!

The acoustics plates where 65kg/m^3, now out of production. The replacement they refer to is rockfon industrial (black, opal, natural) and they are 70kg/m^3. Unfortunately only available in 5cm thickness. For 6" thick, you'll do fine with standard flexi A plates at about 30 kg/m^3.

Wouldn't 95kg/m^3 absorb more of the lower frequencies than 30? Thanks

Man, before you do anything else do yourself a favour and do a little reseach for heaven's sake. Or else you will blow your money and time for no result. We have too many members here that sit in bad rooms that have eaten up their resources.

The short answer to your questioin is NO. The correct answer is 'it depends'.

This question has been covered over and over in this forum. Please. There is a search function.

http://www.bobgolds.com/AbsorptionCoefficients.htm

Check it out for your self my friend.

You got there lab tests of many brands different densities gaps no gaps.

Sorry, but my research lead me to believe that denser is better.
On this forum I've found several quotes similar to "(...)the rule of thumb is that denser is better", "(...)for up to 6" use denser materials".

Would you mind elaborating on when "it depends"?

I also found these absorbtion coefficients
http://www.sheffins.co.uk/Literature...xible_slab.pdf found in this thread.

I'm just trying to learn, and I'm greatful for all insights.

Thank you

Thank you, Sebastian. This is great thumbsup

Really?!

How many times have many stated the advantages of using low density 'generic' pink fluffy stuff Fiberglass for use in Superchunk corner bass traps INSTEAD of the higher density materials?

You maybe have read what you state, but that has not been the message here for quite some time.

I see. But I'm not building super chunks. I'm building 6" panels.
I'm really confused now. The last link provided showed the RXL40 to have the highest overall absorbtion on a 4" 100mm panel. Can I assume that they would work even better at 6" 150mm?

Thanks for helping out.
The Flexi A-plates is starting to look like a good solution.

And where did you get the idea that porous 30 kg/m³ 6" panels are effective as bass traps, which even with a 6" gap drop off dramatically below ~200 Hz.

They will work fine for broadband panels, but they simply lack significant low end extension.

One will also note that according tio the BBC that the "A2 module is not very effective below 125 Hz. Even the D2 module does not absorb much in the lowest frequency bands." p.1

And that assumes Optimal positioning! Just where do you imagine the maximal velocity at the particular low frequency modes to be?

For traps deeper than 12", inexpensive low density 'pink fluffy stuff' generic insulation is most effective.



From Soundflow:

I am sorry but I have to interject here. This keeps coming up despite a whole thread devoted to it. The thread is titled Q4Avare and has all sorts of interesting info on thin panels, airpaps etc. etc.

This notion that thin panels can't absorb bass is simply wrong. Similarly the notion that absorption cannot function well close to boundaries, where particle velocity is low, is also simply wrong.

To the best of my knowledge, and I am sure Andre will have a link to the actual tests, 6 inches of fibre plus a 6 inch gap is similar to the 12 inch deep designs tested by the BBC. They provide essentially flat absorption down to 50Hz.

Frederik, there are tests comparing the various corner designs at studiotips.com
You will see that bigger, thicker are better. However the simple panel straddling a corner is best value for money. In the comparative test the straddling trap is only 24 inches wide, and stands up quite well to the much much bigger 34 inch wide designs.
Many panels traps use 50-100KG fibre.


DD

Please read here

Knauf tp 416 ecose insulation.

Could someone help out interpreting material's gas flow properties

NASA, LF Absorption and Gas Flow Resistivity

On this forum I've found several quotes similar to "(...)the rule of thumb is that denser is better", "(...)for up to 6" use denser materials".

It depends on the thickness of the absorber that you are willing to sacrifice.

You did not say that explicitly before. Still, there is an optimum gas flow resistivity for 6" panels, and that is lower than for the material that you suggested.

Download the porous absorption calculator here and insert some values yourself:

Porous Absorber Calculator V1.58

BTW if you check the details you see this:

4" OC705 on 16 " air absorbs worse at 125 Hz and actually at most higher frequencies than 4" 703, and the highest absorption under those conditions has the lightest material, OC701. How can that be if denser material always absorbs better?

Also, if you look down in the table for the 1240-80 material you will see that they only published one value for 6", and that is the 1240 stuff which is lighter than 1260 or 1280. Is that because they forgot to make two more measurements before printing their submittal sheet? No, it is because this (the lightest, well .. relatively lightest material of the three with 64 kg/m³) is what they recommend for best performance - for 125 Hz and above - at 6" flush mounted (A mounting means flush mounted to the wall).

(BTW there is a typo in this table since 1280 is 128 kg/m³, not 96).

That's not correct. I recently bought these in 10 cm thickness. They come in same sizes as rockwool akustikkplater. 3, 5, 7,5 and 10 cm thick.

For 15 cm (6") thick panels I would put 10 cm and 5 cm rockfon panels together. You also have rockwool murplater with a density of 45 kg/m3. Not sure which will be better, but my guess would be the rockfon for this size.

Flexi-A panels are too fluffy for 15 cm thickness, I would think. I wouldn't use that density other then in panels thicker then 25 cm or large superchunks.

Intuitively (yes, I know, it is dangerous in acoustics ), I would have thought that denser materials would be relatively reflective to high frequencies at lower angles of incidence. Which is particularly relevant for first-reflection point absorbers.

anyway, to answer your question: What are you trying to do? I would suggest that 95kg/m^3 Rockwool is denser than necessary for most applications in a studio.

I'm "simply" trying to build bass traps which are 150mm 6" thick (or thicker if that's better). And I'm trying to find out which rockwool is best for the purpose.

Up to now we did not see any single calculation or even estimation of yours, despite the many hints we have provided.

You will probably end up buying what feels best to you or what you think has been recommended most often and install it at the places that you think might be best. But up to now you know nothing about what will happen with any of those materials between 30 - 100 Hz. Your result will reflect this to a certain degree - most probably you will have too much mid and treble absorption and still unresolved bass problems. Just saying.

Treating a room is not as simple as "ah, they sell these fibre panels as 'bass traps', so let me put a lot of them into the corners". That is a myth, and not a good one.

All the best to your project nevertheless!

It is no harm to question the conventional wisdoms and assumptions now and again. After some research though.
You should be able to find the BBC tests by searching. BBC documents
Or ask Andre. From memory I believe the fibre they used was very light. My sense is that it would be 15-30KG.

If you are doing 6 inch or deeper traps we are looking at a frame here. Don't forget the stuff will sag so provide horizontal supports, e.g. wires or mesh.
Light attic insulation fibre or rock or Ecose will all work just fine. To be sure of success why not go the full 12 inches deep rather than 6 plus 6 air. That stuff is cheap.

You might do well to check out Hannes posts here over the last few months. He has achieved remarkable results with large thick fibrous treatment.

DD

I know and it seems everyone is a bit cranky around here.heh If you are building a 6" panel then got with the 3 or 4 pound.

If we are writing about the BBC research that I think we are, the material was identified as RW2. That is a nominal 32 kg/m³ which is 2 lb/ft², which shows the origin of the 2. I leave it to the readers to guess what RW is short for.

Andre

No kidding.
He can't get rockwool in 3 or 4 pounds though. It has to be either 2.8 or 4.3 punds. heh
I would go with 4.3 (70kg/m3) for 6" panels and 2.8 (45kg/m3) for thicker ones. thumbsup
Thicker then 6" would be better.

Next week I'm going to compare and meausure 20 cm (8") panels with both 65 kg/m3 and 45 kg/m3 rockwool. My guess is that 65 kg/m3 will perform a little better in the midbass and the 45 kg/m3 somewhat better below 100 Hz. We'll see.

bwo, good on you for testing. For instance we have no test to show that light fibre is better than dense, in a SuperChunk. Despite this, many of us are taking it as a probability. Some caveats re tests.
Density is not everything. Different materials of the same density have very different absorption. Many are better than OC for example.
Tests need large samples to deliver a clear result.
45KG seems close to 60KG IMHO, I doubt that the differences will be large.
Changes in absorption have different effects depending on location. Around the speakers they may change the FR a bit due to SBIR. At the back and elsewhere, changes will be best observed in the modes.

DD

Yeah, not much difference in the comparison I did.
Comparing superchunks w/different densities

I can agree with this. thumbsup

Thanks for all the help guys!

I know I have a lot to learn, so I really do appreciate all the help and information you're giving me. As for calculations; it's very hard for a novice to calculate anything just with a bunch of numbers. I'm not as educated as many of you.

Thanks a million