Author Topic: Rockwool density for bass traps  (Read 5398 times)

Offline Vince MacMahon

Re: Rockwool density for bass traps
« Reply #30 on: July 04, 2020, 04:00:42 PM »
Decided to dress up rest of current panels,

Itís Labour intensive to do panels, if I were to do it again Iíd just contact Keagan (from OxlandAcoustics) and save myself the time and the hassle. Yeah ~R1500 a panel but no headache, tools that are pricey and a day gone.  Time lost time never gained.






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Marantz - B&W - SVS - AudioQuest

Offline Tetrasect

Re: Rockwool density for bass traps
« Reply #31 on: November 22, 2021, 09:34:01 AM »
Hi guys,

This might blow your mind but I'm here to tell you that you are wasting money on these high-density panels.

Common 12kg/m3 pink fibreglass insulation is multiple times more effective than those high density rockwool/fibreglass boards.

Turns out the thickness of the panel is the most important aspect that controls absorption. A high density panel is only more effective than a low density panel when it is also very thin, and as we know, the thinner the panel, the less effective it is overall.

Since we want a more effective panel overall we want a thicker panel, but when you increase the density of a panel beyond a certain point, it actually becomes less effective and starts reflecting sound rather than absorbing it.

Here are some graphs to prove it:





So let's compare 3 panels of similar weight using the 3 different materials:



As you can see, with an absorption coefficient at low frequencies up to something like 40 times higher than high density rockwool, the normal old pink fibreglass insulation from builders warehouse blows these high density panels out the water with a serious bang!


Flow resistivity figures used:
50kg/m3 Rockwool = 15,000 Pa*s/m≤
120kg/m3 Rockwool = 60,000 Pa*s/m≤
12kg/m3 Pink insulation = 5,000 Pa*s/m≤

These were taken/averaged/guessed using this resource: https://www.jochenschulz.me/en/blog/rockwool-glasswool-hemp-best-absorber-material
Porous Absorber calculator used: http://www.acousticmodelling.com/multi.php


PS You can also make a 300mm panel with a 100mm air gap and the results are almost identical to a 400mm panel, meaning you can make 3.3 standard size (1200mmx600mm) panels from one roll of pink insulation (currently R399 at builders warehouse).


« Last Edit: November 22, 2021, 09:51:49 AM by Tetrasect »

Offline Vince MacMahon

Re: Rockwool density for bass traps
« Reply #32 on: November 22, 2021, 10:31:32 AM »
I tried that pink stuff, not fun! Too lose and fibres going everywhere.

The rockwool I used was efficient and did a better job in practice. The graph does illustrate that Its more effective,

300cm is 30cm the size of a ruler, thatís taking more space than necessary.


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Marantz - B&W - SVS - AudioQuest

Offline Tetrasect

Re: Rockwool density for bass traps
« Reply #33 on: November 22, 2021, 10:54:26 AM »
I tried that pink stuff, not fun! Too lose and fibres going everywhere.
Yeah, working outdoors and wearing gloves and a mask is a must (maybe even some goggles).

300cm is 30cm the size of a ruler, thatís taking more space than necessary.
Sure, if you are space constrained it might not be an option, though putting some pillars in the corners shouldn't be a problem for most rooms and the space taken by the numerous thinner panels required to match the absorption level of one thick one will probably take up even more space.

Offline Timber_MG

Re: Rockwool density for bass traps
« Reply #34 on: November 22, 2021, 10:55:24 AM »
Hi guys,

This might blow your mind but I'm here to tell you that you are wasting money on these high-density panels.

Common 12kg/m3 pink fibreglass insulation is multiple times more effective than those high density rockwool/fibreglass boards.

Turns out the thickness of the panel is the most important aspect that controls absorption. A high density panel is only more effective than a low density panel when it is also very thin, and as we know, the thinner the panel, the less effective it is overall.

Since we want a more effective panel overall we want a thicker panel, but when you increase the density of a panel beyond a certain point, it actually becomes less effective and starts reflecting sound rather than absorbing it.

Flow resistivity figures used:
50kg/m3 Rockwool = 15,000 Pa*s/m≤
120kg/m3 Rockwool = 60,000 Pa*s/m≤
12kg/m3 Pink insulation = 5,000 Pa*s/m≤

These were taken/averaged/guessed using this resource: https://www.jochenschulz.me/en/blog/rockwool-glasswool-hemp-best-absorber-material
Porous Absorber calculator used: http://www.acousticmodelling.com/multi.php


Unfortunately those flow resistivity values are far off from the stuff available locally. Paid the school fees.

Offline Tetrasect

Re: Rockwool density for bass traps
« Reply #35 on: November 22, 2021, 11:07:39 AM »
Unfortunately those flow resistivity values are far off from the stuff available locally. Paid the school fees.

Does the local stuff have higher or lower flow resistivity than the US/UK stuff?

Offline Timber_MG

Re: Rockwool density for bass traps
« Reply #36 on: November 22, 2021, 11:13:32 AM »
Let's say depending on manufacturer and moon phase the range has been half an order of magnitude at the same density.

Offline Tetrasect

Re: Rockwool density for bass traps
« Reply #37 on: November 23, 2021, 11:39:44 PM »
Let's say depending on manufacturer and moon phase the range has been half an order of magnitude at the same density.

So the fact remains, higher thickness and lower density panels are multiple times more effective than those thin and high density ones.

Sorry to blow up the thread but this is reality.

Thick, low density panels, are the most effective bass traps. You can quote me on that.

Do the calculations and back me up please?
« Last Edit: November 23, 2021, 11:44:25 PM by Tetrasect »

Offline Greyman

Re: Rockwool density for bass traps
« Reply #38 on: November 24, 2021, 07:02:39 AM »
In my space, I have had great success with low-density insulation, but using velocity trapping on a pressure zone will never be the most effective solution.

I do think the quoted density on these products and then the results these calculators spit should not be taken as the gospel, but simply used as a guideline.  :clap:

Offline Timber_MG

Re: Rockwool density for bass traps
« Reply #39 on: November 24, 2021, 08:34:01 AM »
In my space, I have had great success with low-density insulation, but using velocity trapping on a pressure zone will never be the most effective solution.

I do think the quoted density on these products and then the results these calculators spit should not be taken as the gospel, but simply used as a guideline.  :clap:

Exactly. The SA market sells rock wool by density with ZERO thought as to parameters that make the material less dangerous regards chronic health conditions NOR acoustic performance. Please use liners with the stuff.

The models give one an understanding of the design fundamentals, but they are hard to translate accurately (half an order of magnitude in flow resistivity) which is why super chunk traps are often over-specced regards density. Glass fibre is worth the price delta when looking at acoustic performance.

Also very few people treat enough surface area at that thickness to make the performance really count. Most situations with a fixed intervention budget benefit more from placement and properly (not audyssey) aligning multiple subwoofers by analyzing the first three axial modes in each direction and by shaping the early sound field slightly with well placed diffusion and conventional absorption.