John Sayers' Recording Studio Design Forum Archive

New poster here, but I've visited the forum several times in my research. I've searched through several threads on comparisons between mineral wool and fiber glass, but have a question I wasn't able to find a specific answer to:

I am considering building unframed panels (wrapped in polyester fabric, glued, with bolt/washer and wall hanger attachments (using glue/adhesive around the bolts to bond some rigidity with the fiber glass - maybe a bad idea, but frames are the backup plan).

Is there a difference between mineral wool and (for example), OC 703 - is one or the other easier to work with?

My reason for the question is quite simply the wide range in price:
I can order Owens Corning 703 (2", 2'x4') for about $15/sheet but the same supplier sells 6 sheets of mineral wool board (48sq ft) of 2" mineral wool panels for only $29. Why the large price difference - just the nature of fiber glass vs. mineral wool in general? If mineral wool disintegrates more easily, I would probably go with fiber glass simply for sake of convenience. If there is no difference, price wins.

The mineral wool seems to be 8lb density, where I was mainly looking at 3lb density fiber glass boards. The rep I called was fairly helpful with describing the differences, but wouldn't give their own opinion on the difference.

Thanks!

For some reason (probably manufacturing cost) mineral wool is always cheaper; absorption, given same density, seems to track nearly identical between the two.

However, you're talking about 8 PCF instead of 3 PCF; for all but 90 degree incidence, there's a high probability that the higher density stuff won't absorb as well at higher frequencies; it's too dense, so instead of "soaking in" at an angle, the sound tends to reflect causing a lower absorption coefficient at these higher frequencies.

One way around this (sorta) is to put some NORMAL density fiberglass (or some types of polyester) insulation in FRONT of the 8 lb. rockwool; this gets into a "sandwich" thing though, and makes construction less straightforward.

Handling-wise, the rockwool is usually stiffer (especially 8 PCF) and scratchier, but for frameless mounting it would retain its shape better.

Performance-wise though, I'd try to find some lower density rockwool or do the front cover thing I mentioned - exceptions might be if your room is already dead enough in the high end, then the 8 lb. stuff may be just what you want... Steve

Thanks Steve - that's the kind of info I was looking for. I had considered mixing densities in layers to ensure higher freq. absorption, so I may do a mix and match if I can't find the density I need locally - that will split the difference on cost at least.

Regards,
Dedric

You may want to think about just starting with the 8Ib wool and see how it works. We use 8Ib wool in our panels and find it absorbs at 125hz and 4000hz almost equal. That is on the 4" panel

Glenn