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Discussion Starter #21
Wel, since part of my room is pretty much square; I have a very strong peak in that part of the room, in addition to the same nulls. This results in a very uneven response.
Now, I have a pretty flat response from about 22Hz up to about 47Hz, but from there and up to about 83Hz, it is poor.

If you want; I can post a couple of graps and waterfalls :)

You see, I don't have that much money at the time, so I prefer cheap sollutions. And sollutions that's not to dominant in the room.

Thanks for answering ;)
 

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Hi ,

I'd begin by feeding your room dimensions through a program like ModeCalc , to see if you can figure what boundary dimension is causing your spectral 'hump' ... Even better , go here http://www.hunecke.de/en/calculators/room-eigenmodes.html... which will show you the planes/positions where that stationary wave will be sitting .... An effective pressure-quelling device anywhere in that node will reduce the whole thing ( a little ) ... it need not be in a corner ( though corners are eloquent .. in that they do two surfaces at once ... )
Regards trapping devices to use ... only a Helmholtz , polycylindrical , or panel trap will be rationally effective ... as long as it's placed on the node .... Conversely .. putting your sub on a node will be a very bad place for even reproduction from it .... Panel traps are easier to design ... the critical variables being density ( surface mass ) of the front panel ... and depth of box ... Adding some internal damping ( not touching the front panel ) will lessen the 'Q' of the trap's resonance ... making it's effect less narrow in frequency ...

Try here http://www.mhsoft.nl/Helmholtzabsorber.asp for the formulae ....

My suggestions for 'cheap' .. use an actual pressure-active device ... and put it where it will be most effective ....
 
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Discussion Starter #23 (Edited)
Hi, thanks for those great links ;)

But I don't know if I can trust what the model in the first link shows me, because my room isn't square, it is like this:
Uten-navn.jpg

I have thought of "corner traps" made of regular Rockwool or Glava insulation in the three corners in the square part of the room. In total four units which are 110cm tall; one behind each speaker, and two on top of each other in the last corner.
Would that do any good?

Acording to the schematics I get from entering 3,7 x 3,7 x 2,2m in on the first page you linked to; that should help on about every frequency, eccept 78Hz, which is a result of the room height alone. (all this depends on me understanding the figure right).

In addition to that, the plan is to buy a medium thick floor carpet (not wall to wall, but regular "square" one), and to install a thick curtain to separate the two "room parts" from each other.

But wil it help installing those four corner traps, you think?
And what kind of damping material and design should I use?

EDIT: on the drwing of the room, white walls = concrete, and blue walls = wooden panel on top of concrete (with no insulation between).
The far left wall with the window in is not white, it is gray, and is allso wooden panel on top of concrete.
The room is in a basement, so all the walls contains concrete, including the floor, which is hardwood directly (I tinhk) on top of the concrete floor.
 

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Hi ,

Lovely plan ... but horrid shape .... In terms of symmetry of longer-pathlength , less coherent sound , your idea of a curtain would be helpful ...
With walls of massive construction .. they won't be helping with bass trapping ( as a more flexible wall might ) .. so bass control will be more difficult for you ....

'Traps' which aren't airtight ... and constructed from porous materals ... are not designed to reduce pressure .... though they provide that function moderately , if thick enough ... Angling across a corner is one way to get ( at least through the central airspace ) a thicker device ... They will also have significant absorption effects ... I prefer panel traps .... which can be far thinner ... and not take out mids/highs ...

So yes ... thick corner absorption , fairly deep will make a difference .... Calculate that the deepest depth of the airgap ( plus absorption ) should be 1/4 of the length of the wave you intend 'trapping' .... ~ 3.6 feet for ~ 78 Hz ...

I'm not sure if you understood the 'eigenmodes' page ... You pump in your dimensions ... and select ( put black dot in ) the frequency you're interested in .... and it's position will be displayed in the box on the right ... You'll soon see the fundamentals lie on the walls whose dimensions define it ... whilst secondary modes fall 1/2 way along that dimension .... etc .. etc ... As these relate to the room boundaries ( they're stationary .... not bouncin' about ) .. your room shape is less critical to the bottom end ....

Heres another reference ... this time very detailed ( and yes it's talking Tube traps ... but the principles are the same .. )

http://www.asc-hifi.com/articles/iar89.htm

Suggestion for 'thick curtain' ... try a movers blanket ... In the interests of symmetry , run it the whole back wall ... Also , you might slide your system slightly to the left ... so it's on the midline ....

If you do go porous 'traps' ... use the heaviest fibreglass ( 6kg/m2 ) you can .. at least 4" thick ... It might be cheaper to use two thinner ones , sandwiching a rubber , or lino , core .... Wrapping them in chicken-wire further extends their bass absorption ....

Cheers ...
 
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Discussion Starter #25 (Edited)
Ok, so I have to have these huge corner traps to absorb anything in the lower areas?
I was thinking about a size with about 0,5 meters (20"), from the corner to the middle of the outside. Using some 60x120cm insulation "blankets" og "plates" to get 4 triangular.

I was kind of hoping that it would be enough with something stretching about 40cm (16") out on the walls from the corner. Is there any way I can get down to that size without narrowing the "frequency range" too much?

Would any of these two DIY sollutions work you think?: http://forum.studiotips.com/viewtopic.php?t=536

EDIT: or maybe this will work?: http://www.teresaudio.com/haven/traps/traps.html
 
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Discussion Starter #26
OK, no answer.
A more direct question then: Will it help with a membrane absorber?

I'm thinking of this design:
Uten-navn.jpg

Based on a 3mm (1/8") thick plate with dimensions of 60x120cm (24"x48"). About 2/3 full of insulation.
One in each corner behind the speakers.
It is a sealed design by the way.

No effect? Better or worse than a "superchunk" design?
Is this one too small?
 

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It's a waste of a good corner IMO. If you have a live room, you need Full Broadband absorbtion - not something 2 octaves wide at most which is what a real membrane will give you. Do you have any idea what this trap tunes to? Do you know how to calculate it? You give the thickness of the front but don't specify the material. Without knowing the MASS of the front, we can't calculate anything. Also, the absorbant should be within 1/2" of the membrane and likely only needs to be 1-2" thick. A chunk like that behind a membrane of that thickness is most likely a waste of material.

Normally, membranes are used at the ends of a specific dimension where a specific issue is identified. For instance, you might use a membrane in the middle of the rear wall of a room to kill a length related issue without adding more high frequency absorbtion.

Also, you may find that you'll get more and better responses if you start your own thread instead of coming in at the end of someone elses.

Bryan
 
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Discussion Starter #28
OK, I don't mean to be nagging people.

And no, I have noe idea which frequency this one tunes to.
I'll start my own thread then, that might increase the responce as you say ;)
 

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Hi,
My name is Carlos and I'm from Spain.

I'm going to make my own super chunky bass traps following all your exposed info.
But is quite hard to find the right materials in my country.

The most popular panels brand in Spain is ROCKWOOL, so I can choose between 2 models:

Rockwool E-520: 115Kg / m3 density.

Rockwool E.525: 150Kg / m3 density

I'm sorry for the links (they're spanish links) and the metric system measures, so I don't know the conversion value.
I've tried to find international links but I couldn't
Although the first one is cheaper, I've found a store with a little sale stock of the second one, and I get a 25% discount on it.

It will be too much density the 150Kg/m3 panels for my bass traps? I'm wondering about to make 4 super chunky corner traps and 4 broadband panels.

What do you think about it?

Thanks in advance

I'm sorry but I can't put links in this post
 

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The lighter material will work just fine pending thickness

Bryan
 
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