Insulation Thickness Question For Absorbers

R

ram3n

New member
My goal is to get absorbtion down to appx. 500Hz... lower if possible... in my front and rear wall absorbers. It seems the two most popular type of insulation are rigid fiberglass and a semi-rigid mineral wool.

People familiar with these are well aware of the price difference...
3" - 2'x4' Mineral Wool = 0.30 per sq ft.
2" - 2'x4' Rigid Fiberglass = 0.96 per sq ft.
Obviously, big difference.

In my design, I had planned to use 6" (2 layers of 3") of mineral lifted 3.5" from wall in my front and rear absorbers. So will this get down to about 500Hz, or do I need to use rigid fiberglass to get there?

The reason I want to get down to about 500Hz is because these will be complemented with slat resonators that will absorb in the range from about 200Hz-500Hz (maybe a bit lower if I'm lucky).

Thanks.
 
what Reverb Decay time are you shooting for...

If this is a tracking room then .3-.5 sec is usually Okay

If it's a Mixing/Control Room then you want about .3s.

List your Room dimensions, wall and floor coverings, windows, curtains (list areas FT**2 for each) and state the desired Reverb Decay time. I'll calculate a rough treatment and post it.

How narrrow are your slats and how much surface area.
 
This is for a control room.

My room dimensions are 9' wide by 12'-3" long.
I orginally had a 8'-1" concrete ceiling, which I've already applied 1 layer of 3" rockwool to (so I guess that makes my ceiling 7'-10")... that dramatically reduced the reverb time... it was really, really bad at first. I'm pretty sure that the rockwool on the ceiling just reduced the highs, not too much in the mid or lows.

One wall is covered with standard drywall, the other three are covered with what a lot of people called soundboard... but it's still along the lines of basic drywall.

The floor is thin carpet on concrete.

I have one window which allows me to see into the live/studio room. It is not located behind my console, it is actually in the wall to my left. So the wall behind my console and monitors (the direction I'll be facing) is available for treatment. The window is 2' high by 3'-6" wide.

I haven't built the slot resonators yet, but I used the Helmholtz calculator to determine my frequencies, and I'm confident that I can get it down to 200Hz.

My plan was to put front and rear wall abosrobers, corner slat resonators and slat resonators on the walls to my left and right.

This should be enough info for a rough treatment.
 
i hope to have you a rough estimate by Saturday.

also, 2" of glass fiber has an absorption coefficient of .8 at 250Hz and 4" is near .8 at 125Hz. so you can get a good bit of absorption with both 2" and 4" glass fiber. if you space it out from the wall, the absorption coefficients go up.

you also may want to consider mixing in significant amounts of diffusion, so the absorption does not suck up all of your sound energy.
 
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Does anyone have some absortion coefficients for mineral wool?
I have some absorbtion coefficients for the rigid fiberglass board, and I'd like to have something to compare to.

I am planning to put diffusion on the side walls, and I will have slat resonators in the corners, which will diffuse highs.

And is 6" of mineral wool lifted 3" to 4" off the wall overkill as far as absorbtion is concerned?
As Sonixx said, I don't want to suck all the "life" out of the music.
 
hey ram3n,

here's a rough calc for your room. from these numbers the room reverb time looks pretty good, but a bit on the dry side. but, as the reverb times stand, theres no room (reverb decay time surplus) to add any treatments for Early reflections and if you have any furniture, this is not considered, which would tend to absorb even more and bring the reverb time down. the reverb time also depends on what you want to do with this room. if its for both tracking and mixing, i'd suggest you raise the reverb time to about .5 sec.

also, i recommend that you consider removing half the Rock Wool and then lets recalc and go from there. but first, i'd try to analyze the room to determine if it measures close to this calc. consider ETF by Acoustisoft.

note that this calc does not addess room modes. if i get a chance i'll run a calc on modes ASAP.

regards,
-keith
 
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unfamiliar concepts

Hello, can someone explain a little about these absorbers? What are you using to determine what it is your trying to do with them? Are you trying to shorten an RT-60, or something like that. I am completely unfamiliar with these. I guess what I'm trying to ask is "what is it that tells you that you need them, and what is it that you modify to make them do it better or in a different way? Thanks now!
fitz:)
 
Sonnix - Thanks for the analysis. I'm currently out-of-town... that's why it has taken me a while to get back to you. I had planned to put the rockwool on the ceiling before I left, but due some things that came up, I only put up one bundle (32 sq ft). According to your calculations, that's a good thing. And the stuff I put up there can easily be taken down. So maybe you could run the numbers again and give me some advice on how to treat the room from scratch.

And since I'm out of town, I probably won't be able to check this forum for a day or two.
 
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