Rockwool density for control room/studio dividing walls.

markb · Post by **markb** » Thu Jan 12, 2006 3:00 am

I've always thought RWA45 (45kg/m3) was the stuff to use - will this be sufficient if I were to use a traditional two leaf wall, with a 12" gap between 2 5/8" layers of plasterboard per side? Or should I be looking at 60kg/m3?

Cheers

Al

Deluks · Post by **Deluks** » Thu Jan 12, 2006 8:02 am

I don't think it matters inside the walls, use whatevers cheapest. Thicker is better though.

knightfly · Post by **knightfly** » Sat Jan 14, 2006 7:57 am

Right; inside walls, anything from 3 PCF (48 kG) DOWNWARD is fine - in fact, normal spun fiberglass batts of around 1 PCF (16 kG) do as well, within 1-2 dB, as the heavier stuff. If money's tight, I recommend normal spun glass (if it's cheaper) inside the walls, save the more expensive stuff for surface acoustic treatments which the 45 kG stuff is just fine for... Steve

markb · Post by **markb** » Mon Jan 16, 2006 5:46 am

So your saying I can use 16kg/m3 within each 2x4 frame of my two leaf wall, and still get isolation from drums, Marshall Plexis etc?!

Al

Deluks · Post by **Deluks** » Mon Jan 16, 2006 7:29 am

markb wrote:So your saying I can use 16kg/m3 within each 2x4 frame of my two leaf wall, and still get isolation from drums, Marshall Plexis etc?!

Al

If it's max isolation you require, then I'd concentrate more on the walls themselves instead of whatever insulation you put inside. If it's drums then consider more layers of plasterboard, maybe 3 a side, or more! (Although this much weight could be a problem if you're not on a ground floor/solid base.)

Think of the insulation as the cherry on the cake, but worry more about the cake itself.

Ok that sounded silly but you get my drift...

Post by **sharward** » Mon Jan 16, 2006 8:13 am

How about: "Think of insulation as the barbecue sauce on the beef, but worry more about the beef itself."

markb · Post by **markb** » Mon Jan 16, 2006 11:04 am

Cheers for the replies.

Thats very interesting that the less-dense insulation works as well. So if I were to use this design:

3 x 16mm (5/8") plasterboard - 2x4 filled with 16-20kg/m3 insulation - 5" air - 2x4 filled with 16-20kg/m3 insulation - 3 x 16mm (5/8") plasterboard

Would I have sufficient isolation from heavy drums/screaming guitar halfstacks (assuming my ceilings/floors etc) were built and sealed correctly? I'm trying to build enough seperation between my studio rooms and my control room...

Does it matter whether I use rockwool (or equivalent) or can I use your bogstandard pink loft insulation (the fibreglass stuff)?

Cheers for the help

Al

Dan Fitzpatrick · Post by **Dan Fitzpatrick** » Mon Jan 16, 2006 12:55 pm

Mark,

Those are pretty good walls. However one thing you do want to do is FILL the gap between the leaves with insulation. Don't just fill the 2x4 space.

Tests I've seen, sorry I can't give a reference off the top of my head, i believe it was from a IRC report, show that the more of the void that is filled the better, by a significant amount.

Don't worry about leaving a 1 inch gap either, just fill 'er up. it's not going to couple the leaves unless you super-stuff it.

Also if you fill up the void it is more fireproof as a side benefit.

The "rule of thumb" about using standard pink insulation inside walls is correct, but it is a little bit of an oversimplification. From what I recall, the pink stuff is at least as good as the more dense insulation in the lowest frequencies.

Denser insulation does perform better in midrange and high frequencies as I recall. BUT, since the problem frequencies are the low ones, this is frequently ignored and so the basic rule is that pink stuff is fine.

However a few months back when I found some Rockwool for a price equal or less than what i could buy the pink stuff for, i jumped on it because it can only help. But if i run out of rockwool i may just finish up with pink stuff, because i mainly care about the lows.

Hope that make sense.

Dan

knightfly · Post by **knightfly** » Tue Jan 17, 2006 4:34 pm

This is another one of those intuitive (NOT) things about acoustics - within the range of maybe 0.8 PCF to 4 PCF, in-wall insulation gives better LOW frequency performance when it's at the LIGHT end, and better MID/HIGH frequency performance when it's at the HEAVIER end - one theory suggests that the heavier stuff tends to act as a "third leaf" which doesn't help LF isolation.

USG did a study several years ago that showed 2.5 PCF as optimum across the board, but if you're building a high-mass wide gap wall I'd go lighter on the insulation; the highs will be stopped by the mass anyway, and the lows are what's gonna get through. Heaviest I'd go in a wall would be 2.5 PCF, and mostly I'd just use some of the newer, slightly denser "fluffy stuff" that's available.

Inner walls - NO PAPER, NO FOIL, just insulation. Outside walls - if you use anything at all, just paper - and put it against the INSIDE of the wall, NOT in the MIDDLE (believe it or not, even this thin paper can actually cause a degree of LF problems from 3-leaf effects)

For metric, multiply the above by 16 to get kG/m^3... Steve

And as Dan pointed out, FILL it but don't STUFF it much...