Knauf Fiber Glass ?? for ceiling

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larrye

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I just recently posted some pic of my finished control-tracking room. Now it's time to treat it. I have a low ceiling over my studio table (6'9") that John said to treat first. He didn't say specifically how though. But from his site and other threads I think I should use rigid Knauf fiber glass board. I have found a supplier but the thickest they stock is only stock 2" and they don't have it plain. They have it faced in a 3lb/cubic foot ASJ . This is faced in some kind of white material. The other side is plain.

The weird thing is the specs. for this board. They look totally different from those at John's site. I think this is due to the facing material, because the plain specs. are the same. Here are the specs for sound absorption I got from .

at 125Hz = .75 @250Hz = .71 @500Hz = .80 @1000Hz =.66
@4000 Hz = .65 and the NRC = .65

Now I know the SAC should be lower at the lower freq. and they are for the plain untreated 2", so it has to be the facing, right?

I would like to purchase this tomorrow night, but I afraid that it won't work right. I think I like these specs. though.

Questions
1. Would this board be good for treating my ceiling?
2. Should I install it with the facing out, which I think
would yield the above specs.
3. Install with the facing in yielding reversed SAC's

Thanks,

Larry
 
I read that the facing material turns the otherwise open absorber characteristics of fibreglass into more of a tuned panel absorber type.

Anyway back to you question I have used faced rockwool for absorbers with the faced side innermost so as not to mess with the high end frequency absorption. The facing material on the boards I had was "tissue faced" - it's a vapour barrier I think it's basically the same as ASJ - the specs look very similar.

Cheers
 
Transputer,
Thanks for your input. The reason I planned on installing it with the facing out was that it would be more of a tuned absorber.
It seems from reading John's site most problems stem from too much high end absorbtion and now enough on the low end of the spectrum.

Am I correct in this type of thinking?

thanks,

Larry
 
Interesting Larrye - I didn't notice that product. But as you say it does seem to act as a panel absorber which really helps the low-mid absorption. Yeah I'd try it :) BUT not in your particular situation. Your problem is that low ceiling over your console which the standard Kauf rigid would be best suited. You want to stop those short early reflections in the highs as well.

Is it expensive??

cheers
john
 
Larry,
Yes you are right with the panel absorber comparison.

The other consideration is fabric over the 'glass/ rockwool - I used two layers of fabric which itself is a good high end absorber and will take care of much of the high end bounce.I didn't want to take any chances so installed the panels, fabric covered, paper facing innermost. So the facing probably doesn't really effect things much but I suggest use your option 3 for peace of mind. www.customaudio.freeserve.co.uk has some specs for a 6lb cuft fibreglass panel - worth a look.

Cheers
 
Bugger ! John beat me to it ! BTW I am nothing to do with customaudio I just trawl the internet alot...:D
 
John and transputer,

If I understand correctly, in the low ceiling area I should install it faced side to the ceiling which should make it have aprox. the same absorption qualities of the plain. This should increase the SAC from .47 to about 1.06 @ 2000 Hz and from .26 to 1.03 @ 4000 Hz.

1. Put it over the entire low ceiling area?

2. I was planning to build your wall units. Could I just use the Knauf faced side out mounted at an angle, 8" to 0", to break up standing waves? That would be much easier to build, would seem to give about the same absorption qualities as the wall units. Yes ???

3. Cost wise, this faced ASJ 48kg/cubic meter, 2" thick runs $.98/sq ft. This supplier also stocks it in FSK which they said is covered with a silver coating. They didn't know if it was Al foil or not. It is cheaper $.84/sq. ft. They only stock 2' X4' panels.

Thanks again for all your help!
Larry
 
Could I just use the Knauf faced side out mounted at an angle, 8" to 0", to break up standing waves?
Click to expand...

I doubt that it would reflect the lows which is what you are after. It would need to be heavier to work as well as the wall units.

cheers
John
 
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