Rockwool 50kg/cbm v 100kg/cbm (turned into full wall thread)

[bassdropyeah]

Hey guys,
building a studio (semi-) room-in-room with the following layers outside to inside:

Exterior wall - 10cm air - 80mm Rockwool - 12.5mm Knauf Silentboard - 10mm Phonestar quartz sand - 12.5mm Knauf Piano

Does anybody have any experience or measurements on the difference between 50kg/cbm vs 100kg/cbm Rockwool, especially in the frequencies below 100Hz? I couldn't find anything online, people been telling me that it would barely make a difference above 100Hz but i am worried about the bass frequencies.

Is it worth shelling out the extra money? For all 3 rooms that's about an extra 2,500€.

Any other thoughts or recommendation on the build?

Thanks in advance!

[Soundman2020]

Hi "bassdropyeah". Please read the forum rules for posting (click here). You seem to be missing a couple of things!

Does anybody have any experience or measurements on the difference between 50kg/cbm vs 100kg/cbm Rockwool, especially in the frequencies below 100Hz?

Yes. The absorption for 100 kg/m3 mineral wool is significantly lower in low frequencies, compared to 50 kg/m3, as expected fro, acoustic theory.

people been telling me that it would barely make a difference above 100Hz but i am worried about the bass frequencies.

The people you have been talking to don't seem to know very much! There will be a fairly large difference: the absorption for the heavier insulation will be significantly less that for the lighter insulation.

Is it worth shelling out the extra money? For all 3 rooms that's about an extra 2,500€.

I don't understand: Why is the lighter stuff more expensive? That doesn't make much sense. It's usually the other way around! Usually the heavier, more dense insulation is more expensive, so I don't understand why it would cost more to buy the lighter stuff where you live. I would ask the supplier why he is charging more money for a less dense product!

Any other thoughts or recommendation on the build?

What build? You did not provide any information about your build, or even about what you want to use the insulation for. Is it meant to be a damper on your MSM system? A filler for bass traps? Treatment for your first reflection points? Absorption for a tuned device? If you don't explain in detail, the we can't help you very much.

Exterior wall - 10cm air - 80mm Rockwool - 12.5mm Knauf Silentboard - 10mm Phonestar quartz sand - 12.5mm Knauf Piano

Why do you want to use that strange "sandwich" of materials? Do you have some acoustic test information from a reputable lab that shows how such a "sandwich" will perform? Or are you just guessing that it might work?

What are you trying to achieve with that? How much isolation do you need, in decibels, and at what frequencies do you need it?

There's just not nearly enough information in your post to be able to answer your questions, other than the one about the low frequency absorption of dense insulation, vs. lighter insulation. That part is easy to answer, since high density insulation pretty much always has worse low-frequency absorption than the correct density.


- Stuart -

[bassdropyeah]

Hey Stuart,
thanks for your reply. I did indeed not read the rules. Added my location.

Also here is some general information - starting out with the fact that i am not planning this construction, merely trying to help out my friend who is in charge of this because he is under a lot of stress right now both at his other job and with his private life. So i am just relaying some questions we had, without knowing to much about the ideas of the construction myself. I know this is far from ideal but all i can do remotely, so any help still is much appreciated.

We are trying to build 3 production/mixing rooms within a one-floor office building. One big room, concrete floors, two walls are big and solid exterior walls, the other two are less solid and border the neighbour offices. We are splitting our big room into 3 (not rectangular) smaller rooms and need to get the best possible isolation both between each room and to the adjacent offices.

We won't build a full room-in-room for cost and effort reasons. I will try to upload out ground plan/blueprint tomorrow. For now let me try to adress some of your arguments:

I don't understand: Why is the lighter stuff more expensive?

It is not, i assume you misread my post. Obviously the 100kg/cbm is more expensive than the 50kg/cbm.

What build? You did not provide any information about your build, or even about what you want to use the insulation for.

See above, these mineral wool layers are supposed to be a part of the wall in between 2 production rooms.

Why do you want to use that strange "sandwich" of materials?

As stated above, i am not the person who planned this studio, just one of the partners who will be using one of the rooms. But i think the general idea behind this was that several layers of different material with different density give the best overall sound damping over a wide frequency range. Is that completely wrong in your opinion?

What are you trying to achieve with that? How much isolation do you need, in decibels, and at what frequencies do you need it?

As much as possible for a reasonable amount of time & work.

That part is easy to answer, since high density insulation pretty much always has worse low-frequency absorption than the correct density.

Following this rule would mean the 100kg mineral wool has worse LF absorption than the 50kg one? This seems very counter intuitive to me but i would trust your judgement.



I know i come across as absolutely unprepared and clueless, but this is not the case with the person actually planning this, so please bear with me. As i said earler, i am just trying to take some workload of that guy buy helping out with some research.

[bassdropyeah]

Ok so here's some of the plans we made. Groundplan and two views of the walls. Ceiling is similar as wools, just definately the lighet 50kg mineral wool not the heavy one. The floor is a very solid and deep conrete floor. The whole building is a old european industrial building so the exterior walls are really heavy. The side walls to the adjacent offices are also solid stone and not too bad.

Given the fact there are these exterior walls i think this counts as a two leaf wall? With the air in between?
We expect around at least 42dB damping per single wall, 75dB from studio to studio (full two leaf wall w 10-15cm air in between)
The doors we are using are around 42dB too. In the low frequency range my guy expects around 40% of that.
Is this realistic?

The exterior walls are on the sides with the windows, the adjacent offices are on the top and bottom of this ground plan:

groundplan small.jpg

top view.png

side view.png

edit: this sandwich system with 2-3 layers of drywall on top of the mineral wool is actually a recommendation from one of the manufacturers, where i also stole the schematics from.