Help needed desperately: 8# wool and what to do?

StudioInProgress · Post by **StudioInProgress** » Wed Aug 11, 2004 9:51 am

I just received a large order of 8# Roxul Mineral Wool 2" and 4" panels, cost a fortune to have shipped. I did some research before I ordered it but never saw any mention of different weights till now.

Anyway, I plan on building Gobos, Bass traps, Absorption panels and Window Isolation boxes with the stuff. From what I just read 4# is recommended. Am I screwed? Can I use this stuff and somehow improvise and find a workaround for all of the above?

AVare · Post by **AVare** » Wed Aug 11, 2004 11:02 am

Yes you can use it no problem. Have a look at the absorption characterstics for 9 pound and 4 pound mineral wool (eg Roxul, Fibrex) at

http://www.bobgolds.com/AbsorptionCoefficients.htm

BTW it didin;t happen to be important in this case, but read the sticky "Please Update Your Profiles." We have seen people ask "can I get this in neighbourhood" and not even know what continent, much less region they are from.

StudioInProgress · Post by **StudioInProgress** » Wed Aug 11, 2004 12:28 pm

I hope you are right. From what I've read someone claimed that 8# wool acts more like a reflective surface would. That's why I panicked. Anyone else here that can confirm that I am safe using this stuff?

giles117 · Post by **giles117** » Wed Aug 11, 2004 10:46 pm

as the Density of the material goes up it tens to be more reflective at higher frequencies.

I believe you were over on the HR BBS site, not sure if I did a good job of explaining but I will again. if this rockwool is placed behind a slat resonator wall 9for example), great. the wall is already designed to be reflective and the 8# will improve your bass trapping.

However if this rockwool is to be used on an exposed surface in your room (say the back wall of a short control room) then you will run into the reflective characteristics of the density of the material at high freq's which can smear your mix sound field.

Not saying it is the worse thing to do, but not the best.

The 4lb allows you a nice balance in absoprtion over the entire freq range.

In some cases the reflectiveness of it is a good thing as you dont want to over deaden your room either, just be wise in your application of it.

Example for your gobos, when you position your gobos, position them at angles to your source so there is not a DIRECT reflection path back into your microphone. The bass traps?? What design, if it is the corner trap with slats over it design. Great.

And your window boxes if it is just lining the box then you'll be ok there as well.

Finally, As far as an absortion panel, not the best thing to use. Go with the 4# if you can afford it.

StudioInProgress · Post by **StudioInProgress** » Thu Aug 12, 2004 12:05 am

Thanks for the help! I feel like a complete idiot not realizing the density of this stuff before I ordered it. This is a good reason why we should buy local, at least it can be returned easily.

I'll probably use it for the traps and windows and I may just eat the loss and use the 8# stuff somewhere in my house attic for insulation and buy 4# and do it right, at least for the absorption panels and gobos anyway.

knightfly · Post by **knightfly** » Thu Aug 12, 2004 8:47 am

Another option - for acoustic treatments, such as gobos and absorption within the room, you might want to look at putting a layer of the 8# stuff BEHIND a layer of normal "fluffy stuff", the NON-faced kind - this would give you a "mini" version of Philip Newell's rear wall absorption technique, that I've come to refer to as "gradual impedance" absorption - the fluffy stuff is cheap and local, and would increase the HF absorption while the heavy stuff would take care of the lower ferquencies. Sorry I can't quote you exact coefficients, but it should work pretty well.

For inside the walls, you could use part 8# and fill in with the fluffy stuff as well - slightly overfill the cavities, and you'll get damping of your wall panels which helps LF performance several dB... Steve

giles117 · Post by **giles117** » Thu Aug 12, 2004 10:14 pm

That is wild, I had thought of that. But didnt say it. ARRGH!!! But it lets me know this brain is working. Great idea steve. helps eliminate the issue of the reflectivity of the 8# Insul

knightfly · Post by **knightfly** » Fri Aug 13, 2004 1:04 am

Knightfly, AKA Robin Hood - steal from the best, share with the rest...

StudioInProgress · Post by **StudioInProgress** » Fri Aug 13, 2004 7:45 am

knightfly wrote:Another option - for acoustic treatments, such as gobos and absorption within the room, you might want to look at putting a layer of the 8# stuff BEHIND a layer of normal "fluffy stuff", the NON-faced kind - this would give you a "mini" version of Philip Newell's rear wall absorption technique, that I've come to refer to as "gradual impedance" absorption - the fluffy stuff is cheap and local, and would increase the HF absorption while the heavy stuff would take care of the lower ferquencies. Sorry I can't quote you exact coefficients, but it should work pretty well.

For inside the walls, you could use part 8# and fill in with the fluffy stuff as well - slightly overfill the cavities, and you'll get damping of your wall panels which helps LF performance several dB... Steve

Sounds like a great idea! Are you talking the standard faceless pink insulation? If so, can you suggest R value of thickness for the Gobos and Absorption panels? With the Gobos and Absorption panels should I be using my 4" Mineral or 2"? I was going to make my Gobos 6' tall by 4' wide, not sure on the thickness though. Suggestions?

Also, to avoid the fibers coming through the Guilford of Maine fabric I was about to order, would I need to cover the insulation with something?

I appreciate everyone's help!

knightfly · Post by **knightfly** » Fri Aug 13, 2004 9:09 am

There are as many ways to build a gobo as there are DIY studio guys - I've not gotten into the specifics of what different designs would accomplish in this vein yet, I'll try to work out a few ideas as time permits - generally, total thickness of a gobo should probably not exceed 4", 6 at most. This would limit you to using the 2" heavy stuff, with unfaced R-11 fiberglass over.

Containing the fluffy stuff can be done with cloth if it's not too "overstuffed", or expanded metal mesh.

You can use garbage bags or other light plastic over absorbent to contain fibers, it only affects the "sizzle", or high frequencies - makes things brighter, which is normally not a bad thing. When recording, you're always better off cutting frequencies than boosting them because boosting always adds noise and phasing problems; so, if the room's a bit bright (the tracking room, that is) it's better than being too dull.

More when I get a chance - I'm expecting the arrival of Dr. Cox's new ($150) book on absorption soon, so I'll be realizing just how dumb I am once again

Always depressing, this is my form of masochism I guess... Steve

StudioInProgress · Post by **StudioInProgress** » Fri Aug 13, 2004 11:47 am

On the Gobos, with R-11 (3 1/2") and my 2" wool I'll come in at 5 1/2" + 1/2 for some reflective back. I was going to build the Gobos with absorption on the front and a reflective surface, maybe 1/2" plywood on the back covered in Guilford of Maine fabric. That would put me at 6".

I'm way open for Gobo design suggestions.