Questions on corner traps...

[Blueeyedfrog]

I'm new to the forum and have just built my first DIY sub. The sub's great but I have a very uneven response curve. So I think bass traps are the next step (BFD on order). I was intending to use 3 inch thick fiberglass across the corners with airspace behind but I see you have totally filled the corner. Is it better to fill the corner than leave air space or is this just a different approach?

[atledreier]

I have 4" Rockwool straddling my corners, and it's pretty effective. I've got more panels on the way and I'm gonna make 'proper' corner traps like the OP did. I think they'll be more effective, as there's a lot more material to absorb the energy. I'll make sure to do before and after analysis when I finish them.

[chas]

Is it better to fill the corner than leave air space or is this just a different approach?

Hi Blue - Hopefully one of the experts on the forum can answer this. Bryan??

I'll make sure to do before and after analysis when I finish them.

Maverick - Looking forward to the analysis...something I never found time to mess with.

[Bob_99]

chas wrote:
Hi Blue - Hopefully one of the experts on the forum can answer this. Bryan??

Maverick - Looking forward to the analysis...something I never found time to mess with.

I'm not an expert, but the more thickness that you have, the lower the frequency that will be affected and that's always good.

Bob

[bpape]

Sorry - out of town with limited connectivity.

Full corners will in fact extend the bottom end control lower in frequency. From a cost perspective when DIY'ing, the same amount of material to build a chunk will be used for 6" thick straddling panels - IOW, 50% more than a 4" panel straddling.

Bryan

[Blueeyedfrog]

Thanks everyone for your answers.

If I'm not mistaken, blanket insulation appears to be cheaper than the more rigid sheets. In order to save costs would it be a good idea to use sheeting across the corner and fill the space behind with the cheaper blanket filling. Or would the blanket compress too much under its own weight? Unless you could use vertical runs (stand the insulation on end rather than stacking wedges on top of each other as done here) and glue them together to reduce sagging?

Cheers,
Blue

[yourgrandma]

I belive the idea with the rigid fiberglass is that it is denser than batting, thus absorbing more sound, rather than allowing it to pass through. If you have an air space anyway, I can't see any harm in it, but it would be a mess.

I'm thinking of building some corners while I'm off work, but its cold out and I dont feel like wasting a hundred pounds of LP heating my shop. I wonder if anyone has done corner traps with full squares, protruding into the room. I'm trying to envision how I'd cover them.

[bpape]

Blanket will require more thickness to compensate for the lower density. If you want to fill the back with batting, use at least 4" of board on the front and fill in with the lower density. It's still not as good as solid 3-6lb/cu ft density material but better than just 4" straddling.

Bryan

[eugovector]

yourgrandma wrote:
I wonder if anyone has done corner traps with full squares, protruding into the room. I'm trying to envision how I'd cover them.

I think you'd open yourself to lots of damage from people brushing up against the sharp corner and breaking it down, all the while using twice as much material as necessary. And it would look weird

Marshall

[Prof.]

Blueeyedfrog wrote:
Thanks everyone for your answers.

If I'm not mistaken, blanket insulation appears to be cheaper than the more rigid sheets. In order to save costs would it be a good idea to use sheeting across the corner and fill the space behind with the cheaper blanket filling. Or would the blanket compress too much under its own weight? Unless you could use vertical runs (stand the insulation on end rather than stacking wedges on top of each other as done here) and glue them together to reduce sagging?

Cheers,
Blue

Hi Blue...Using corner chunks for bass traps can get quite expensive here with Australian products...
I used 4 layers of 2" semi rigid fibreglass..
The inner layer is about 150mm wide and fits into the corners, and each layer gets progressively wider, to form a sort of a wedge shape, with a small amount of air space between each layer.

If you want to use the US OC703 equivalent for your corner traps, you will need Bradfords "Supertel" fibreglass..
It comes in 1200x2400 2" thick sheets. costs about $70.00/sheet.

Doing it this way you will only need one sheet per corner..

[Blueeyedfrog]

OK, so using blanket/batts is a bad idea. Glad I got that one straighten out.

However, I'm a bit confused because I have been trying to compare coefficients of Australian products and it seems that, for a given thickness, the same density blanket has similar coefficients as the rigid board: http://www.bobgolds.com/AbsorptionCoefficients.htm

As an aside, I have noticed that the Australian products appear to be nowhere as high as the US OC703/5 coefficients - why?

Also, when comparing the Bradfords "Supertel" fibreglass to the Bradfords Fibertex650 the coefficents are respectively, 0.39 and 0.59, for 2" board. Surely higher coefficients are better - i.e. OC703 is around 0.60-0.80?

In fact which of these would people recommend:

Ultratel - 0.34, density 2.4kg/m2
Quietel - 0.36, density 6.5kg/m2
Supertel - 0.39, density 1.6kg/m2
Flexitel - 0.42, density 1.2kg/m2
Fibertex650 - 0.59, density 5kg/m2 (but horrible 11500 x 900 [4.6' x 3'] sheet sizes)
or
Insulco semi-rigid IB - 0.46, density ?

Also, some of the coefficients change depending on whether or not the sheets are covered with foil. Presumably if stacking then foil is unnecessary/non-beneficial? I notice that higher coefficients do not correlate with higher density - which is better, higher density or higher coefficient or both high density and coefficient?

I have no idea of the price variation across the different products - so that also may be a deciding factor... yes insulation is expensive here in Aus.

Re using squares instead of triangles - won't that create two corners in the space where there was previously only one?

Cheers,
Blue

EDIT:

Just wanted to check my calculations to make corner wedges:

My ceiling is 2400mm high

1200 x 2400 sheet = 32 triangles; 600mm (2') across the hypotenuse.

32 triangles @ 50mm thick stacks to 1600mm high

1600mm height x 3 sheets = 4800 = enough material for two floor-to-ceiling bass traps

@ $70 per sheet that's $210 for two traps + covering

Cheers,
Blue

[eugovector]

Blueeyedfrog wrote:

1600mm height x 3 sheets = 4800 = enough material for two floor-to-ceiling bass traps

@ $70 per sheet that's $140 for two traps + covering

Cheers,
Blue

When stacked, the fiberglass will compress slightly. Be prepared to have some extra in the stack, or just leave a little space at the top and use a fabric frame to cover the whole mess.

[bpape]

Again, for the same size triangle, a solid triangle will take the same amount as 3 2" layers straddling. Fluffy in the back is OK if you still do 4" on the front.

Bryan

[Blueeyedfrog]

Thanks Bryan,

Any suggestions as to the best material to use for the straddling (Ultratel, Quietel, etc.)?

Cheers,
Blue

[Prof.]

Blueeyedfrog wrote:

Also, some of the coefficients change depending on whether or not the sheets are covered with foil. Presumably if stacking then foil is unnecessary/non-beneficial? I notice that higher coefficients do not correlate with higher density - which is better, higher density or higher coefficient or both high density and coefficient?

I don't know whether it's better to have high coefficient or higher density...All I know is that the "Supertel" does a good job in the configuration that I'm using..

Blueeyedfrog wrote:

Just wanted to check my calculations to make corner wedges:

My ceiling is 2400mm high

1200 x 2400 sheet = 32 triangles; 600mm (2') across the hypotenuse.

32 triangles @ 50mm thick stacks to 1600mm high

1600mm height x 3 sheets = 4800 = enough material for two floor-to-ceiling bass traps

@ $70 per sheet that's $210 for two traps + covering

By my calculations you only get 16 triangles with a 600mm face from a 1200x2400 sheet!!

[yourgrandma]

Okay, I'm sorry but I've been having a hard time tracking this stuff down. Do I need to go directly to a contractor supplier, or what? Heck, the chain stores have never even heard of it.

[Blueeyedfrog]

I don't think you can buy the stuff I mentioned above (#11) in the US. I think everyone there uses the Owens Corning 700 series Rigid Fiberglass, specifically the 703 FRK or 705 FRK, which seems to have better specs than the Australian stuff I mentioned.

[yourgrandma]

I forgot where you were. I guess I meant the 700 series stuff. Sorry for the confusion. I guess I could've picked a better thread to jack.

[Blueeyedfrog]

A 600 x 600 square can be cut diagonally giving 4 wedges (each with 600 across the longest face), yes?

8, 600 x 600 squares can be cut from 1, 1200 x 2400 sheet, yes?

8 x 4 = 32, no?

[Blueeyedfrog]

Feel free to jack the thread - this one started from another thread I jacked!

Here: http://www.hometheatershack.com/foru...-finished.html

[yourgrandma]

Sonnie's always on top of that, isn't he! I did that once and he created a new thread before I even checked it for replies. Very good admin skills.

[Prof.]

I stand corrected...I did my calculation using 600mm.sides..not faces..

[Blueeyedfrog]

Does anyone know whether corner traps will have any effect as low as 20-25hz? Basically I have a drop off there and that's the area I want to improve.

[atledreier]

And while we're on the subject of faces, will longer faces (splitting a 120x60 sheet in 4, 85cm face) yield better results? Reach lower and/or provide more damping? You'd think so anyway, it's twice the amount of material. But I won't use it all if there's no real benefit.