# My Corner Absorber Design and q's about Australian materials



## Kaisergrendel (Jul 19, 2011)

Hi! This is my first post here, I'm totally new to audio and acoustics and I'm looking at building broadband corner absorbers for my living room. I live in Australia so obviously don't have access to US materials. I contacted a local business and have been quoted on the following materials:

Rockwool 350

Thickness: 25mm or 50mm
Density: 60 kg/m3
Flow Resistivity: 2.2 x 10,000 mks Rayls/m

Absorption coefficient:

125 250 500 1000 2000 4000 5000 NRC
Plain
25mm 0.18 0.29 0.69 0.86 1.05 1.2 1.16 0.71
50mm 0.21 0.69 1.13 1.15 1.16 1.18 1.14 1.05
Faced
25mm 0.14 0.38 0.87 1.07 1.06 0.9 0.79 0.85
50mm 0.31 0.83 1.16 0.99 0.9 0.78 0.73 0.9

Quietel

Thickness: 25mm
Density: 130 kg/m3
Flow Resistivity: N/A

Absorption coefficient:

125 250 500 1000 2000 4000 5000 NRC
Unfaced 13 0.06 0.08 0.28 0.62 0.86 1.06 1.04 0.45
Unfaced 25 0.07 0.28 0.74 1.04 1.13 1.09 1.11 0.80
Unfaced 50 0.36 0.81 1.12 1.18 1.11 1.12 1.22 1.0

Since the general consensus seems to be that the recommended density for 4"-6"(100-150mm) traps is about 60kg/m3, but I want to preserve as much space as I can, I'm considering using twice the density for half the thickness. Looking at these specs, would the Quietel work close to as well as the Rockwool 350?

Second question: The attached picture shows my plan for the corner trap as a usable shelf, right above the subwoofer. The door (which will contain insulation and isn't shown) will be attached to the structure with cabinet hinges. Assuming I put holes in each shelf surface to make a contiguous air column, does anyone know how well this would work as an absorber? My goal is just to make the listening experience in my living room more comfortable - I'm not too concerned about getting the graph ruler flat. Thanks!


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## bpape (Sep 14, 2006)

Doubling density will not make up for half the thickness or even close. If you want to get the bottom end under control, you're better off to use 4" of the lighter density than 2" of the higher density by a LONG way - and at basically a wash in cost. Ya just can't fight physics - sorry.

Bryan


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## dean70 (Jun 27, 2008)

You could use this: http://www.tontineinsulation.com.au/images/docs/Tont_Acoustisorb_3_Version%2010s.pdf

I am currently redoing a room using this as my acoustic panel material and getting good results so far (using REW measurements before and after). I used 1x 50mm and 1 x 100mm to make 150mm thick x 600 wide corner panels.

This can be purchased from http://www.insulationbattsaustralia.com.au/ They will deliver to your door.


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## Prof. (Oct 20, 2006)

That corner shelf unit would be ideal for corner chunks...Triangular sections cut from 50mm. semi rigid fibreglass and stacked on top of each other..
The ideal material to use is Bradfords Ultratel..It's a little bit denser than the Quietel..

You really need two corner bass traps to be affective..Is there a corner on the other side of that opening?


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> Doubling density will not make up for half the thickness or even close. If you want to get the bottom end under control, you're better off to use 4" of the lighter density than 2" of the higher density by a LONG way - and at basically a wash in cost. Ya just can't fight physics - sorry.
> 
> Bryan


Thanks, got it.



dean70 said:


> I am currently redoing a room using this as my acoustic panel material and getting good results so far (using REW measurements before and after). I used 1x 50mm and 1 x 100mm to make 150mm thick x 600 wide corner panels.


Thanks, I was considering this at first but had second thoughts when I saw that it cost $85 to deliver metro. Does this mean to all cities' metropolitan areas or just Sydney?



Prof. said:


> That corner shelf unit would be ideal for corner chunks...Triangular sections cut from 50mm. semi rigid fibreglass and stacked on top of each other..
> The ideal material to use is Bradfords Ultratel..It's a little bit denser than the Quietel..
> 
> You really need two corner bass traps to be affective..Is there a corner on the other side of that opening?


Yes indeed the other side is an opening, hence I'm only building the one cabinet on the left. See the pictures below. I reckon I could do with just treating the upper corner on the right. The opening leads to the dining area, kitchen and then narrowing down to a corridor to the back of the house. Kind of like a transmission line come to think of it. Do you think think I need to do anything else do the right corner?

Take note that the cabinet doesn't exist at the moment, I have to design and build it. My idea is to use the air gap as a light storage space to help with the MAF (mom approval factor). I agree that the cabinet would do great as a superchunk container, but I have enough trouble getting permission to take up that space at all. I'm just wondering how the extra timber would affect the behavior of the trap.


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## Prof. (Oct 20, 2006)

Unfortunately there's not a lot you can do on that right side..
Any non symmetrical layout presents problems when it comes to controlling the acoustics..
It would be better to have the chunks right up against the corner without the cabinet, but it will still be affective with them in the cabinet..

My suggestion would be to put a corner trap up in the right hand side corner..It's not much area but it will help a bit..and I would also put corner traps in the back wall corners..
Also you really need to put down a throw rug in front of the unit to give further dampening..


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## dean70 (Jun 27, 2008)

Kaisergrendel said:


> Thanks, I was considering this at first but had second thoughts when I saw that it cost $85 to deliver metro. Does this mean to all cities' metropolitan areas or just Sydney?


Costs $85 to Melbourne and come in packs of 3 - 2400x1200mm size. May not be worth the cost if you are only doing one corner.


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## Kaisergrendel (Jul 19, 2011)

Prof. said:


> Unfortunately there's not a lot you can do on that right side..
> Any non symmetrical layout presents problems when it comes to controlling the acoustics..
> It would be better to have the chunks right up against the corner without the cabinet, but it will still be affective with them in the cabinet..
> 
> ...


Do you think that since it's an opening there'd be less need for treatment there though?

Yes, it's a shame about the symmetry but this is the best arrangement we could do with the limited space, so I'm going to work with it  A superchunk would be great but for the reasons mentioned before I'm going to put a 100-150cm panel door on that cabinet instead and fill the door itself with insulation.

Good idea on the throw rug, though in the actual living room there is already one there. I forgot to render it :blink: Actually let me throw up a more complete rendering of my living room...

Ok so you can see in the animated GIF how the door (filled with insulate) would work on the cabinet. There's also a rug on the floor and two heavy ottoman stools straddling the left corner. We didn't add those with acoustics in mind but I imagine they help a bit.



dean70 said:


> Costs $85 to Melbourne and come in packs of 3 - 2400x1200mm size. May not be worth the cost if you are only doing one corner.


I'll need maybe two bags since I'm doing a little more than one corner. Will see, thanks for the info!


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## bpape (Sep 14, 2006)

With the right side open, treating the left corner is actually 'creating' your symmetry (or at least better replicating it). Given that there isn't a corner for waves to build up or to provide any sort of gain, killing the left corner is actually more closely replicating what the right corner isn't doing.

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> With the right side open, treating the left corner is actually 'creating' your symmetry (or at least better replicating it). Given that there isn't a corner for waves to build up or to provide any sort of gain, killing the left corner is actually more closely replicating what the right corner isn't doing.
> 
> Bryan


Thanks for confirming this Bryan, that's the understanding I'm basing this layout on.


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## bpape (Sep 14, 2006)

Just understand that it's only doing this in terms of the corners. It's not going to address the fact that the L and R speakers are going to have completely different boundary gain characteristics due to the lack of a full wall behind the right speaker.

Bryan


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## Kaisergrendel (Jul 19, 2011)

bpape said:


> Just understand that it's only doing this in terms of the corners. It's not going to address the fact that the L and R speakers are going to have completely different boundary gain characteristics due to the lack of a full wall behind the right speaker.
> 
> Bryan


Understood. I can live with that until I get my own house :T


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## Prof. (Oct 20, 2006)

Kaisergrendel said:


> A superchunk would be great but for the reasons mentioned before I'm going to put a 100-150cm panel door on that cabinet instead and fill the door itself with insulation.


I take it you mean that the corner door panel will be 100-150mm. in thickness and filled with insulation..Like an acoustic wall panel only it will be hinged!
That being the case..it should work quite well..:T


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## Kaisergrendel (Jul 19, 2011)

Thank you all for your kind advice. It was a great help! I won't be making the traps for awhile but when I do I'll be sure to post them here. Thanks again!


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