3 pcf or 6 pcf

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IraqiFreedom

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I've decided to build my own 4" bass traps from fiberglass.

But I can't decide how dense the fiberglass should be.

It appears there is some debate about 3 vs 6 pcf. What is the latest thinking/experience?

Also, I have a high ceiling and had an idea to hang standard rolls of insulation from the ceiling, maybe 8 rolls in a checkerboard dangling about 8 inches below ceiling. Would this be worth a try?
 
The thinking hasnt change go no higher than 4pcf. Any higher the panel starts to act like a wall. all reflective and stuff. 3-4pcf gives the best balance of absorption over the entire freq range.

As for me and my desire to never spend more than I have to, i used Semi-Rigid Rockwool. :)
 
IF,

For bass trapping I'd definitely go with the 6 pcf type. For mid/high frequency absorption 3 pcf may be a better choice because it reflects a tiny bit less up there.

--Ethan
 
Looking at these specs for Roxul Rockwool, it seems to me that the 4# does have better absorption in higher freqs, however not by a lot really. The 8# has better absorption in the lower freqs, also not by much but still quite a bit when you think how much harder it is to get the lows. I would think that by going with the 8# you could absorb more of the lows and less of the highs and get a flatter room. Am I wrong in my thinking?

fucanay
 

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Not quite. The hardness/Density of the 8# will result in your highs getting reflected back at you.

So the 4# is the better balance between bth objectives.

I have the 4# behind me in my studio and my Bass meters flat.

Bryan Giles
 
Not to mention that the 8lb stuff is most likely close to twice as expensive...air costs nothing.
 
I ended up buying a couple boxes of Knauf 'ASJ' 2" 3 PCF which I got for $1.30 sf.

3.0 PCF ASJ 2" .75 .71 .80 .66 .41 .24 .65

So I took the 12 panels out, wrapped them in large plastic bags and stacked em up around the room just for some preliminary listens and it made a *huge* difference. So I got excited and started making some traps.

I started with a 4" trap and hung it up on the front middle ceiling/wall corner, dangling down about four inches from the ceiling and 4 inches off the wall. Should I tighten that up?

I had the ASJ facing on the outside of the joined 2" panels, Like this []

key= asj facing side --> [ <-- plain side

Funny thing, I think it sounded worse after I put that first panel up there.

So I am thinking about changing the config to ][ or [[.

The ASJ membrane seems pretty reflective just looking at it. It does make it easy to staple the covering on it.
 
The facing is quite reflective. What I would suggest is seeing if you can carefully remove the facing from the outer panel without pulling too much fiberglass with it. With the facing still in the middle your 4 inch panel will simply not act like a 4 inch panel.

for a bass trap ideally you will remove the facing from both panels...yes I know that will make them harder to cover. But for bass traps you want to hang them a little away from the wall with an air space behind the trap so that the sound travels through the panel, bounces against the wall, and then has to travel through it again on the way back.
 
Thanks, Innov.

Removing the ASJ membrane is easy. I had an idea to leave a few key patches on it for stapling. Anyways these panels are going to work wonders. The bass is already tighter and can only get better.

My small room sounded pretty good with bluegrass and stringy stuff, but rock sounded horrible. I will soon be in maggie ecstasy. Thanks to all the members of the board for all the great information.

I'll post the final results and response plots in a couple weeks.

One last question: My room has a funny space to the left of the front wall where there is attic access. (4x4x10) I'd rather not plug it with sheet rock (although I could)

Would a bass trap plugging the gap (essentially making traps to plug the wall look ok?

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