Will this rockwool work for me?

[midoban]

Hi, i'm doing some acoustic treatment and want to make some absorbers. i've read that rigid fiberglass with a density of 45 kg/m3 is good for that, but in a store close to my home i found some rockwool with a density of 80 kg/m3 in a good price, will it be good or should i keep searching for a 45 kg/m3 fiberglass/rockwool?

[DanDan]

Go with it. 80K should be fine unless your are building deep traps. e.g. over 6 inches. When deep, lighter fibre performs better and is much cheaper.

DD

[Jens Eklund]

Originally Posted by DanDan

Go with it. 80K should be fine unless your are building deep traps. e.g. over 6 inches. When deep, lighter fibre performs better and is much cheaper.

DD

On what do you base these guesses on?

Using the Miki or Deleany-Bazely models (empirical), the absorption coefficient falls below 0,8 (1,0 being max) at about 1,3 kHz if 6” of 80kg/m3 Rockwool, compared to about 200 Hz if 25 kg/m3.

[PaulRain]

everything depends on the thickness of the panel you are planning to make and for what use.
Bass Traps? Early reflections? Real low Bass traps?
for example, talking about rockwool, if I'm planning to make 50mm panels I will buy 80 kg/m3 but I know they are not going to be usefull under 200Hz, but at that thickness lower densities are less interesting.
I will (personal opinion) always choose to buy less dense material and double/triplicate/quadruplicate the thickness......
If I'll build a panel today I will do it at least 200mm thick using the less dense material I find according to the costruction I choose, sometimes fluffy insulation is not easy to use to build panels.

[midoban]

Originally Posted by PaulRain

everything depends on the thickness of the panel you are planning to make and for what use.
Bass Traps? Early reflections? Real low Bass traps?
for example, talking about rockwool, if I'm planning to make 50mm panels I will buy 80 kg/m3 but I know they are not going to be usefull under 200Hz, but at that thickness lower densities are less interesting.
I will (personal opinion) always choose to buy less dense material and double/triplicate/quadruplicate the thickness......
If I'll build a panel today I will do it at least 200mm thick using the less dense material I find according to the costruction I choose, sometimes fluffy insulation is not easy to use to build panels.

as i understand form my research, if you put the rockwool diagonally over a corner of the room, it functions as a bass trap. so my plan was to get a good amount of that 80kg rockwool and use it for both early reflections (flat and spaced out from the wall) and for bass traps (diagonally over room corners).

so about the thickness, the rule of thumb is that the more dense it is, the better it functions on low frequencies (bass)?

[Jens Eklund]

Originally Posted by midoban

so about the thickness, the rule of thumb is that the more dense it is, the better it functions on low frequencies (bass)?

No; opposite, assuming very thick. If not, it will never be effective at low frequencies unless converted to a pressure-based absorber:

Slotted panel vs. wool only (measured):



Marked lines: slats (70x16 mm) over 70 mm wool with different slot-widths.
Thick line (no markers): no panels, only 70 mm wool.

[midoban]

Originally Posted by Jens Eklund

No; opposite, assuming very thick. If not, it will never be effective at low frequencies unless converted to a pressure-based absorber:

Slotted panel vs. wool only (measured):

Attachment 243427

Marked lines: slats (70x16 mm) over 70 mm wool with different slot-widths.
Thick line (no markers): no panels, only 70 mm wool.

ok, so from what you're saying, i'm better off getting the 45 kg/m3 (instead of 80) for the early reflections on the side walls, and use it also for bass traps on walls corners but with more layers to make it thicker.

[Jens Eklund]

Yes.

[midoban]

Originally Posted by Jens Eklund

Yes.

Thank you.

[Max Dread]

Or fill the corners completely (instead of using straddled panels) a la superchunks..... in which case you can use light fluffy loft insulation. Just need to think about how you will support it to prevent it compressing..... But it would be both an effective and cheap solution.

[midoban]

Originally Posted by Max Dread

Or will the corners completely (instead of using straddled panels) a la superchunks..... in which case you can use light fluffy loft insulation. Just need to think about how you will support it to prevent it compressing..... But it would be both an effective and cheap solution.

mm.. well, for the bass traps i was thinking of just leaving an air gap between the diagonal panel and the corner where the walls meet, like this:

(a look from above)

you think i should fill this gap with a fluffy materiel?

[Jens Eklund]

Originally Posted by midoban

you think i should fill this gap with a fluffy materiel?

If 20-30 kg/m3 or less, then yes:

http://www.gearslutz.com/board/5999249-post4.html

[midoban]

Originally Posted by Jens Eklund

If 20-30 kg/m3 or less, then yes:

http://www.gearslutz.com/board/5999249-post4.html

i see, well mine would be 45 kg/m3 so i can leave it empty.

[Glenn Kuras]

Actually from all the data I have seen using higher density, when straddling corners does work better (to a certain point of thickness). See the following density report by Ethan.
Rigid fiberglass density tests

[ciro]

Originally Posted by Jens Eklund

No; opposite, assuming very thick. If not, it will never be effective at low frequencies unless converted to a pressure-based absorber:

Slotted panel vs. wool only (measured):

Attachment 243427

Marked lines: slats (70x16 mm) over 70 mm wool with different slot-widths.
Thick line (no markers): no panels, only 70 mm wool.

http://www.gearslutz.com/board/6796933-post7.html

Like this, Jens (looks like ~10mm slot )? A question: there´s some "right" way to put the slots(like glue, for example)?

The numbers are impressive, I think is the first time I see the comparison this way, different slots in the same graphic.Thank you.

Ciro

[midoban]

Originally Posted by Glenn Kuras

Actually from all the data I have seen using higher density, when straddling corners does work better (us to a certain point of thickness). See the following density report by Ethan.
Rigid fiberglass density tests

Interesting, from these tests, its clear that the 80kg/m3 is better then the 45kg/m3 when straddling corners. and i'm sure not gonna go above 6", even not above 3".

so its safe to assume that up to 6" thick, the more dense it is, the better it is for low freqs absorption? that's the opposite of what we said until now.

if thats the case, i think the best combination for me is to get the 80kg for the straddling corners and the 45kg for the early reflections side walls.

very helpful tests by the way!

[Glenn Kuras]

Originally Posted by midoban

Interesting, from these tests, its clear that the 80kg/m3 is better then the 45kg/m3 when straddling corners. and i'm sure not gonna go above 6", even not above 3".

so its safe to assume that up to 6" thick, the more dense it is, the better it is for low freqs absorption? that's the opposite of what we said until now.

if thats the case, i think the best combination for me is to get the 80kg for the straddling corners and the 45kg for the early reflections side walls.

very helpful tests by the way!

Let me point out one thing though (sorry to do a little flip flop) you may find that 45kg/m3 is much less in price, so as far as "bang for the buck" I would recommend it.

[midoban]

Originally Posted by Glenn Kuras

Let me point out one thing though (sorry to do a little flip flop) you may find that 45kg/m3 is much less in price, so as far as "bang for the buck" I would recommend it.

its fine, these opinions help me a lot. the money is no issue here, these materials are so cheap.. and i already found a 80kg/m3 for a good price as i stated in the main post. so its really up to whats better for the goal.

as i said, my corner traps aren't gonna be thicker then 6" so i think the 80kg/m3 is better according to the tests.

now the question is if i need 45kg or 80kg for the side walls.

[Jens Eklund]

Originally Posted by ciro

http://www.gearslutz.com/board/6796933-post7.html

Like this, Jens (looks like ~10mm slot )? A question: there´s some "right" way to put the slots(like glue, for example)?

Yes, 10 mm slits (7,7 % perforation) over 200 mm 6 kPa*s/m² wool (no air-gap). Useful absorption between approximately 70 to 180 Hz. Usually you glue and screw the slats to the frames.

[Jens Eklund]

Originally Posted by midoban

now the question is if i need 45kg or 80kg for the side walls.

http://www.gearslutz.com/board/6280707-post37.html
50 kg/m3 or lower if thicker than 50 mm (no air-gap).

[DanDan]

Jens-

On what do you base these guesses on?

Using the Miki or Deleany-Bazely models (empirical), the absorption coefficient falls below 0,8 (1,0 being max) at about 1,3 kHz if 6” of 80kg/m3 Rockwool, compared to about 200 Hz if 25 kg/m3.

DD- I can never tell if Jens really wants to know my thinking, or is this confrontation for it's own sake. A quick search will show far too many examples looking like the latter. However, I will answer, although from a quick scan it is pretty much covered by others.

Many of my 'guesses' come from information supplied by friends.
e.g. Glenn has repeatedly spoken of actual tests he paid for which showed no decrease in LF performance with density in corner straddlers.
I seem to recall 100KG and 6 or 8 inches.
My recommendation that FRK be fully bonded is from another friend.
He also paid for tests. It is generous of both to share such information with us all.

Then there is hypothesis based on test results better than expected....
Not guesses.
Many of us believe in a sort of drum head behaviour, especially in corners, but not exclusively so. It does appear that the more rigid panels have more of this behaviour. It can be encouraged by bonding a foil to the panel.

This behaviour is not included in Whealy and other calculators.
It strikes me as pretty pointless to repeatedly allude that what most of us are doing successfully, cannot be happening, because a list of academics didn't predict it.

For side and particularly overhead reflection duty, light saggy material is a right pain. Frames, meshes etc. become mandatory. With the recommend depths of 50-100mm, hopefully with airgaps, at HF and MF, 80-100KG does a good job and is far easier to do.
This is an experienced opinion, no guess.

DD

[midoban]

Originally Posted by Jens Eklund

http://www.gearslutz.com/board/6280707-post37.html
50 kg/m3 or lower if thicker than 50 mm (no air-gap).

ok, thank you. but i don't quite understand why i shouldn't leave an air gap. isn't it makes the wave return all the way through the rockwool again? (which is good?)

[Jens Eklund]

Originally Posted by DanDan

Jens-


DD- I can never tell if Jens really wants to know my thinking, or is this confrontation for it's own sake. A quick search will show far too many examples looking like the latter. However, I will answer, although from a quick scan it is pretty much covered by others.

Many of my 'guesses' come from information supplied by friends.
e.g. Glenn has repeatedly spoken of actual tests he paid for which showed no decrease in LF performance with density in corner straddlers.
I seem to recall 100KG and 6 or 8 inches.
My recommendation that FRK be fully bonded is from another friend.
He also paid for tests. It is generous of both to share such information with us all.

Then there is hypothesis based on test results better than expected....
Not guesses.
Many of us believe in a sort of drum head behaviour, especially in corners, but not exclusively so. It does appear that the more rigid panels have more of this behaviour. It can be encouraged by bonding a foil to the panel.

This behaviour is not included in Whealy and other calculators.
It strikes me as pretty pointless to repeatedly allude that what most of us are doing successfully, cannot be happening, because a list of academics didn't predict it.

For side and particularly overhead reflection duty, light saggy material is a right pain. Frames, meshes etc. become mandatory. With the recommend depths of 50-100mm, hopefully with airgaps, at HF and MF, 80-100KG does a good job and is far easier to do.
This is an experienced opinion, no guess.

DD

You are assuming that the wool is dense and rigid enough to act as a membrane and this can naturally be the case assuming the construction allows it to move. The center frequency is very difficult to predict and depends on mounting, depth and mass of the panel (and some other parameters not easily sourced). Since you repeatedly point out how “hard” it is to construct a pressure based absorber, I find in odd that you suddenly promote this concept but if you can provide more information on how to predict the performance and especially the center frequency of absorption of this kind of trap, it might be useful.

[Jens Eklund]

Originally Posted by midoban

ok, thank you. but i don't quite understand why i shouldn't leave an air gap. isn't it makes the wave return all the way through the rockwool again? (which is good?)

Check the whole thread.

first reflection panels density and thickness

[Max Dread]

Just to get things straight....

Is a straddled trap of any density likely to perform as well as a superchunk of light fluffy insulation? As far as corner velocity/broadband bass traps go, I thought light fluffy superchunks were king? Especially if the front face can be extended to 34" (giving a 34x24x24 triangle)...

@midoban Incidentally, when I mentioned filling the corner above, I did not mean straddling the corner as you proposed and then filling the cavity with light fluffy. Rather, I was referring to making the whole thing out of light fluffy and then building a simple fabric covered frame (or any other type of device) to hide it.

[DanDan]

Since you repeatedly point out how “hard” it is to construct a pressure based absorber, I find in odd that you suddenly promote this concept but if you can provide more information on how to predict the performance and especially the center frequency of absorption of this kind of trap, it might be useful.

I have always encouraged the most aggressive LF treatment.
I tried Helmholtz, found the forumulae to be incorrect. Found a published example of successful treatment to be a farce. I see very very few examples of helmholtz perf in successful operation. The slatted version is quite popular though. Recently we saw four GS DIY pressure traps fail to perform. I am pretty confident when I say perf and even panel helmholtz are hard to get right, while SuperChunks are easy and always work.

There is nothing sudden or new in my and Glenn's drum head analogy.
Due to manufacturing differences, compression, binders, humidity etc. I would not attempt to predict the behaviour. Why would one want to? It is very broad and benign. There are plenty of tests, private and published, which show the result of this behaviour though. Very broadly speaking it often peaks around 80Hz. Most usefully given typical room dimensions.

You are assuming that the wool is dense and rigid enough to act as a membrane and this can naturally be the case assuming the construction allows it to move.

Again, no assumption, no guess, no prediction.
Tap a RealTrap or other quite rigid panel, you can hear and even measure the resonant frequency.

DD

[DanDan]

Is a straddled trap of any density likely to perform as well as a superchunk of light fluffy insulation? As far as corner velocity/broadband bass traps go, I thought light fluffy superchunks were king? Especially if the front face can be extended to 34" (giving a 34x24x24 triangle)...

SSC's are king to many of us in terms of certainty of successful DIY, cost, and Low LF performance. But we have no comparative proof.
Nobody has treated a room with the options and thus compared them directly.
The only corner absorber test published compares a 24 inch straddler with 34 inch corner fills of the same fibre and foam.
If you try to guesstimate to compare like with like, the corner straddler seems very very nearly as good as the much more expensive full fill.
In bang per buck terms it is the winner.
But it is an extrapolated result, the comparison was not direct and balanced.

Furthermore there was no test of a lighter density SSC which theory suggest should be way better, and would certainly be cheaper than a dense one.

With comparative tests, who knows?
However, Glenn will tell you he has measured useful corner fill SSC performance down at 50Hz.
I have shown a test which shows the large SSCs, 48KG Isover fibre, reduce a 1.3 S 35Hz mode to 0.6 Seconds.

For most people the choice is often down to what material is actually available at reasonable cost locally.

Then we start looking for affordable fireproof fabric which won't let the fibres shed down from the ceiling but will let the sound in.......fun eh?

It is fun when it's done. Even the most basic, termporary, ugly treatment, if based on the sure things, yields wonderful sonic rewards.

DD

[Jens Eklund]

Originally Posted by DanDan

I see very very few examples of helmholtz perf in successful operation.

Look around!

Google

[DanDan]

Look around!

I have done Jens. Tried Wes Lachot and Jeff Hedback's websites. Newell's, Northward. I see slats, more often diffusive than LF tuning. I see lots of Invisible Alpha.

The only decent example of a single successful perf design came from you Jens.
To my knowledge there has not been a second example presented.

You have said before, 'look at any studio on the cover of Mix magazine'.
Actually I did. Nada.

The promotion of a singular technique or aspect of the overall picture seems to me unbalanced. There is little point in encouraging DIY of tuned pressure traps when the readers are often in temporary/rented/small/amateur or prosumer spaces. At least four GS who tried, failed.

While I study and admire the effort, the science, the intelligence, in pro designs, I have worked in quite a few. Far too many don't work well in terms of translation, because the designer didn't have the big picture.
e.g. Flat is not the goal. Nor is a perfect RFZ gap. All of the compromises have to be in harmony for these places to actually deliver. What I have experienced suggests a dearth of actual listening, tuning by ear and experience, focussed on results, i.e. translation,.

DD

[Glenn Kuras]

Originally Posted by midoban

its fine, these opinions help me a lot. the money is no issue here, these materials are so cheap.. and i already found a 80kg/m3 for a good price as i stated in the main post. so its really up to whats better for the goal.

as i said, my corner traps aren't gonna be thicker then 6" so i think the 80kg/m3 is better according to the tests.

now the question is if i need 45kg or 80kg for the side walls.

You could go either way for the side walls. Not to talk you out of 80kg, but when I say straddling corners I mean ALL corners not just wall to wall corners. One other idea if you really are looking for the "king" of trapping then I would go with squares that are 17"x17" to make false soffits that will not only look better but kick some ars down to 40 to 50hz. I would though recommend the 45kg for those. I just tested something close to that at Riverbank lab and was pretty blown away by the results.